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Suzana Matana 8 Fragen

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  1. 1Carbon is a small, relatively light element with [blank_start]four[blank_end] single valence electrons oriented toward
    the vertices of a regular [blank_start]tetrahedron[blank_end]. It can form up to four stable covalent bonds with other
    atoms. Carbon atoms attach to each other to form straight and branched chains and ring structures of various sizes and complexity that act as the [blank_start]backbones[blank_end] of biological molecules. When
    attached to four hydrogen atoms, carbon forms a tetrahedral [blank_start]methane[blank_end] molecule. Although
    the carbon-hydrogen bond is slightly [blank_start]polar[blank_end] (En 0.4), the symmetrical geometry of the
    methane molecule causes it to be [blank_start]nonpolar[blank_end]. Molecules containing only carbon and hydrogen
    are known as [blank_start]hydrocarbons[blank_end]. Larger hydrocarbons are also [blank_start]nonpolar[blank_end] because of the symmetrical arrangement of their bonds. Other elements such as hydrogen, oxygen, sulfur, and phosphorus may attach to the carbon backbone to form reactive clusters of atoms called [blank_start]functional groups.[blank_end]
    1. Abackbones
    2. Bfour
    3. Ctetrahedron
    4. Dmethane
    5. Epolar
    6. Fnonpolar
    7. Ghydrocarbons
    8. Hnonpolar
    9. Ifunctional groups.
  2. 2[blank_start]Functional groups[blank_end] possess certain chemical properties that they impart to the molecules to which they are attached. These groups are more [blank_start]reactive[blank_end] than the hydrocarbon portions of biological [blank_start]molecules[blank_end]. Most of the reactions that occur in living organisms involve [blank_start]functional group[blank_end] interactions. The hydroxyl group, [blank_start]OH[blank_end], and the carboxyl group, [blank_start]COOH[blank_end], are polar because of the electronegative [blank_start]oxygen[blank_end] atom they contain. Sugars and alcohols are highly soluble in (polar) water because they contain polar [blank_start]hydroxyl[blank_end] groups. The carboxyl group, COOH, makes a molecule [blank_start]acidic[blank_end], whereas the amino group, [blank_start]NH2[blank_end] makes it basic. Compounds containing the carboxyl group are organic acids called [blank_start]carboxylic acids[blank_end]. Those containing amino groups are organic bases called [blank_start]amines[blank_end]. Amino acids, the basic building blocks of [blank_start]proteins[blank_end], contain an [blank_start]amino[blank_end] group and a [blank_start]carboxyl[blank_end] group. A number of carboxylic acids are important intermediates in the process of [blank_start]cellular respiration[blank_end]. The phosphate group is found in molecules, such as [blank_start]adenosine triphosphate (ATP)[blank_end] which is used to transfer [blank_start]energy[blank_end] between organic molecules in cells.
    1. AFunctional groups
    2. Breactive
    3. Cmolecules
    4. Dfunctional group
    5. EOH
    6. FCOOH
    7. Goxygen
    8. Hhydroxyl
    9. Iacidic
    10. JNH2
    11. Kcarboxylic acids
    12. Lamines
    13. Mproteins
    14. Namino
    15. Ocarboxyl
    16. Pcellular respiration
    17. Qadenosine triphosphate (ATP)
    18. Renergy
  3. 3There are essentially four major classes of macromolecules in living organisms: [blank_start]carbohydrates,[blank_end] [blank_start]lipids,[blank_end] [blank_start]proteins,[blank_end] and [blank_start]nucleic acids[blank_end]. Complex carbohydrates, proteins, and nucleic acids are [blank_start]polymers,[blank_end] which are composed of long chains of smaller subunits. The most common lipids, [blank_start]triacylglycerols[blank_end] (also called triglycerides) and [blank_start]phospholipids,[blank_end] are not polymers but relatively large molecules composed of several smaller parts. Although the various macromolecules contain different subunits, they are assembled and disassembled in the same way. A condensation reaction also called a dehydration synthesis reaction, creates a covalent bond between two interacting subunits, [blank_start]linking[blank_end] them to each other. This reaction always involves the [blank_start]removal[blank_end] of a hydrogen atom, H, from the functional group of one subunit and an [blank_start]OH group[blank_end] from the other subunit’s functional group.
    The OH group and the H come together to form a [blank_start]water[blank_end] molecule, H2O (from which the terms condensation reaction and dehydration synthesis were derived). This reaction results in a [blank_start]covalent[blank_end] bond between the subunits. Condensation reactions absorb energy in the overall process. They are called [blank_start]anabolic reactions[blank_end] because they result in the construction of large molecules from smaller subunits. A condensation reaction joins monomers into polymers. An [blank_start]OH[blank_end] group from one subunit and an [blank_start]H[blank_end] atom from another join to form a water molecule, resulting in a covalent bond
    between the subunits. This is an [blank_start]energy-requiring[blank_end] process. A hydrolysis reaction uses an OH group and an H atom from a water molecule to [blank_start]break[blank_end] a
    bond holding subunits together. Energy is [blank_start]released[blank_end] in this process.
    In some cases, cells must break macromolecules into their individual subunits. These reactions, called [blank_start]catabolic[blank_end] reactions, break nutrient macromolecules down in the process of digestion. Catabolic reactions occur primarily by a process essentially the [blank_start]reverse[blank_end] of condensation reactions. In this process, a [blank_start]water molecule[blank_end] is used to [blank_start]break[blank_end] a covalent bond holding subunits together. The water molecule provides an H atom to one subunit and an OH group to the other; hence, the name given to this process is hydrolysis reaction (hydro, meaning “water”; lysis, meaning “to break apart). Hydrolytic reactions release energy in the overall process, as illustrated in Condensation, and hydrolysis reactions require the assistance of special protein molecules, called [blank_start]enzymes[blank_end], to take place efficiently. Enzymes are biological [blank_start]catalysts[blank_end], and catalysts are chemicals that speed up chemical reactions without becoming consumed in the process. Enzymes possess special structures that recognize the covalent bonds that must be created or broken.
    1. Acarbohydrates,
    2. Blipids,
    3. Cproteins,
    4. Dnucleic acids
    5. Epolymers,
    6. Ftriacylglycerols
    7. Gphospholipids,
    8. Hlinking
    9. Iremoval
    10. JOH group
    11. Kwater
    12. Lcovalent
    13. Manabolic reactions
    14. NOH
    15. OH
    16. Penergy-requiring
    17. Qbreak
    18. Rreleased
    19. Scatabolic
    20. Treverse
    21. Uwater molecule
    22. Vbreak
    23. Wenzymes
    24. Xcatalysts
  4. 4Carbohydrates are among the most common organic materials on Earth. Millions of tonnes are produced by [blank_start]plants and algae[blank_end] every year through the process of [blank_start]photosynthesis[blank_end]. Carbohydrates are used by organisms as [blank_start]sources of energy[blank_end], as [blank_start]building materials[blank_end], and as [blank_start]cell surface markers[blank_end] for cell-to-cell identification and [blank_start]communication.[blank_end] Carbohydrates contain carbon, hydrogen, and oxygen atoms in a [blank_start]1:2:1[blank_end] ratio. Their empirical formula (the
    chemical formula that shows the ratio of atoms in the molecule in lowest terms) is (CH2O)n, where n represents the number of carbon atoms. Carbohydrates may be classified into three groups: [blank_start]monosaccharides,[blank_end] [blank_start]oligosaccharides[blank_end], and [blank_start]polysaccharides[blank_end]. The simplest carbohydrates are the simple sugars or [blank_start]monosaccharides[blank_end] (mono, meaning “single”; saccharide from Saccharum, meaning “sugar”). The term saccharide and the suffix
    -ose both refer to sugars. Simple sugars contain a single chain of carbon atoms to which [blank_start]hydroxyl[blank_end] groups are attached. Monosaccharides may be distinguished by the [blank_start]carbonyl[blank_end] group they possess—aldehyde or ketone—and the number of atoms in their carbon backbone. A sugar with five carbons is called a pentose, one with six carbons, a hexose. The two simplest monosaccharides are dihydroxyacetone (a triose with a ketone group) and glyceraldehyde (a triose with an aldehyde group) (Figure 6).In addition to the two triose sugars, Figure 6 illustrates two common pentose sugars, ribose (a component of [blank_start]RNA[blank_end]) and [blank_start]ribulose[blank_end] (used in photosynthesis), and three common hexoses, glucose (a source of energy for virtually all cells), galactose (a component of lactose, milk sugar), and fructose (fruit sugar). Another distinguishing feature of simple sugars is the spatial arrangement of their atoms. Molecules with the same [blank_start]chemical formula[blank_end] but with a [blank_start]different arrangement of atoms[blank_end] are called isomers. Glucose (C6H12O6), galactose (C6H12O6), and fructose (C6H12O6) are isomers since they possess the same number and types of atoms, but a different arrangement of those atoms (Figure 6). Isomers possess different
    shapes and different [blank_start]physical and chemical[blank_end] properties. Monosaccharides with five or more carbons are linear molecules in the dry state, but
    readily form [blank_start]ring[blank_end] structures when dissolved in water. Figure 7 shows a glucose molecule forming a six-membered ring. When this occurs, there is a 50% chance that the hydroxyl group at carbon 1 will end up below the plane of the ring. If so, the resulting molecule is called [blank_start]-glucose[blank_end]. If the hydroxyl group at carbon 1 ends up [blank_start]above[blank_end] the plane of the ring, then B-glucose is formed. When glucose dissolves in water, the hydroxyl group on carbon 5 reacts with the aldehyde group at carbon 1 to form a closed ring. If the hydroxyl group at carbon 1 lies below the plane of the ring, the resulting molecule is called [blank_start]-glucose[blank_end]; if the hydroxyl group lies above the plane of the ring, then it is called B-glucose. (b) In the abbreviated formula for glucose, carbon symbols are omitted and constituent groups are projected above and below the plane of the ring. [blank_start]Oligosaccharides[blank_end] are sugars containing two or three simple sugars attached to one another by covalent bonds called [blank_start]glycosidic linkages[blank_end]. These bonds form by condensation reactions, in which the H atom comes from a hydroxyl group on one sugar, and the – OH group comes from a [blank_start]hydroxyl[blank_end] group on the other. Important disaccharides include maltose, composed of two [blank_start]a-[blank_end]glucose molecules held together by a [blank_start]1–4[blank_end] glycosidic linkage; sucrose, composed of [blank_start]a-[blank_end]glucose and -fructose with a [blank_start]1–2[blank_end] glycosidic linkage between them; and lactose, composed of a-glucose and [blank_start]a-galactose[blank_end]. Maltose is a disaccharide found in grains that are used in the production of beer, sucrose is table sugar, and lactose is the sugar normally found in milk. Sucrose is used by many plants to [blank_start]transport[blank_end] glucose and other simple sugars from one part of the plant to another. It is found in high concentrations in sugar cane, sugar beets, and sugar maple trees. The glycosidic linkage between the glucose molecules in maltose is called a 1–4 glycosidic linkage because it forms between the hydroxyl group of [blank_start]carbon1[blank_end] on one glucose molecule and the hydroxyl group of [blank_start]carbon 4[blank_end] of the adjacent molecule. Polysaccharides (complex carbohydrates) are monosaccharide polymers composed of [blank_start]several hundred to several thousand[blank_end] monosaccharide subunits held together by glycosidic linkages. Some polysaccharides are straight chains, whereas others are branched. Polysaccharides serve two important functions in living cells: [blank_start]energy storage[blank_end] and [blank_start]structural support[blank_end]. Starch and glycogen are examples of storage polysaccharides; cellulose and chitin are structural polysaccharides. Plants store the Sun’s energy in the form of glucose and other carbohydrates through the process of [blank_start]photosynthesis[blank_end]. In most cases, plants produce much more glucose than they need for their immediate energy requirements. [blank_start]Enzymes[blank_end] in the chloroplasts link excess glucose molecules to one another, forming starch, the main energy storage molecule in plants. Starch is a mixture of two different polysaccharides, [blank_start]amylose[blank_end], and [blank_start]amylopectin[blank_end]. Potato starch is 20% amylose and 80% amylopectin, by mass. Amylose is a straight-chain of the polymer of a-glucose with [blank_start]1–4 glycosidic linkages[blank_end]. Amylopectin is a branched-chain a-glucose polymer with 1–4 linkages in the main chain and [blank_start]1–6 linkages at the branch points.[blank_end] The [blank_start]angles[blank_end] at which the glycosidic linkages form cause the polymers to [blank_start]twist into coils[blank_end] that make them [blank_start]insoluble[blank_end] in water. Plants store starch as insoluble granules within chloroplasts, amyloplasts, and other plastids. Some plants store large amounts of starch in specialized structures, such as tubers (potatoes), taproots (carrots and turnip), and the fruits of grains (wheat, corn, and rice). Humans and other heterotrophs use the plant’s stockpile of energy as a source of food energy for themselves. Animals possess enzymes that [blank_start]hydrolyze[blank_end] amylose and amylopectin into individual glucose molecules and then extract energy from these molecules in the process of [blank_start]cellular respiration[blank_end]. Excess glucose molecules are linked to one another to form [blank_start]glycogen[blank_end], an energy storage molecule in animals. Glycogen is similar to [blank_start]amylopectin[blank_end] in structure with 1–4 main chain linkages and 1–6 branch-point linkages; however, there are more branches in glycogen. Humans and other animals store small amounts of glycogen in [blank_start]muscle and liver cells[blank_end]. Enzymes in these tissues hydrolyze glycogen into [blank_start]single[blank_end] glucose molecules for energy during bouts of physical exercise. However, glycogen stores are [blank_start]small[blank_end] and are depleted in about one day if not replenished. Glycogen is structurally similar to amylopectin with 1–4 glycosidic linkages between -glucose monomers in the main chain and 1–6 linkages at the branch points. Glycogen is more highly branched than amylopectin. Notice the helical structure of these three polysaccharides. Glycogen granules can be seen in the cytoplasm of animal cells. Cellulose, the primary structural polysaccharide of plants, is a major component of plant [blank_start]cell walls[blank_end]. Worldwide, plants produce approximately 200 billion kilograms of cellulose a year, making it the most abundant organic substance on Earth. Cellulose is a straight-chain polymer of [blank_start]-glucose[blank_end] held together by [blank_start]1–4 glycosidic linkages[blank_end]. Hydroxyl groups at the 1 and 4 positions in [blank_start]B-glucose[blank_end] cause every other monomer to be inverted for the glycosidic linkage to form. Unlike amylose and amylopectin, cellulose molecules are neither [blank_start]coiled[blank_end] nor branched. Their [blank_start]straight[blank_end] shape allows the [blank_start]hydroxyl groups[blank_end] of parallel molecules to form many hydrogen bonds, producing tight bundles called [blank_start]microfibrils[blank_end].
    Many cellulose microfibrils intertwine to form tough, [blank_start]insoluble[blank_end] cellulose fibers that plants use to build their cell walls. Humans have made use of the tough physical properties of cellulose by using it in wood for lumber and paper, and in cotton and linen for clothing. Digestive enzymes in humans are able to break the [blank_start]glycosidic linkages[blank_end] in starch, but humans are unable to [blank_start]digest[blank_end] the linkages between the -glucose subunits in cellulose. Certain animals, such as cows, sheep, and rabbits, contain symbiotic bacteria and
    protists in their digestive tracts that produce enzymes that break the -glucose linkages in cellulose. This allows the animal to digest the cellulose in grasses and other vegetables matter. Although humans are not able to use cellulose as a source of energy, the cellulose in fresh fruits, vegetables, and grains is a healthy part of a well-balanced diet. Cellulose fibers, called [blank_start]roughage[blank_end], pass through our digestive systems undigested and gently scrape
    the walls of the [blank_start]large intestine[blank_end]. This stimulates intestinal cells to secrete mucus, which lubricates feces and aids in the elimination of solid waste. It also helps keep feces moist by binding water in the large intestine.
    The hard exoskeleton of insects and of crustaceans, such as crabs and lobsters, and the cell wall of many fungi, is made of [blank_start]chitin,[blank_end] a cellulose-like polymer of N-acetylglucosamine. This monomer is a glucose molecule to which a [blank_start]nitrogen[blank_end]-containing group is attached to the [blank_start]second[blank_end] carbon position. Chitin is the second most abundant organic material found in nature. Many organisms, such as insects, crustaceans, and mushrooms, have brightly colored exoskeletons made of pigmented chitin. For many of them, coloration is a key to survival, used for defense, concealment, and recognition. Chitin’s physical and chemical properties make it useful in medical applications, such as contact lenses and the tough, yet biodegradable, stitches that decompose as a wound heals.
    1. Aplants and algae
    2. Bphotosynthesis
    3. Csources of energy
    4. Dbuilding materials
    5. Ecell surface markers
    6. Fcommunication.
    7. G1:2:1
    8. Hmonosaccharides,
    9. Ioligosaccharides
    10. Jpolysaccharides
    11. Kmonosaccharides
    12. Lhydroxyl
    13. Mcarbonyl
    14. NRNA
    15. Oribulose
    16. Pchemical formula
    17. Qdifferent arrangement of atoms
    18. Rphysical and chemical
    19. Sring
    20. T-glucose
    21. Uabove
    22. V-glucose
    23. WOligosaccharides
    24. Xglycosidic linkages
    25. Yhydroxyl
    26. Za-
    27. AA1–4
    28. ABa-
    29. AC1–2
    30. ADa-galactose
    31. AEtransport
    32. AFcarbon1
    33. AGcarbon 4
    34. AHseveral hundred to several thousand
    35. AIenergy storage
    36. AJstructural support
    37. AKphotosynthesis
    38. ALEnzymes
    39. AMamylose
    40. ANamylopectin
    41. AO1–4 glycosidic linkages
    42. AP1–6 linkages at the branch points.
    43. AQangles
    44. ARtwist into coils
    45. ASinsoluble
    46. AThydrolyze
    47. AUglycogen
    48. AVcellular respiration
    49. AWamylopectin
    50. AXmuscle and liver cells
    51. AYsingle
    52. AZsmall
    53. BAcell walls
    54. BB-glucose
    55. BC1–4 glycosidic linkages
    56. BDB-glucose
    57. BEcoiled
    58. BFstraight
    59. BGhydroxyl groups
    60. BHmicrofibrils
    61. BIinsoluble
    62. BJglycosidic linkages
    63. BKdigest
    64. BLroughage
    65. BMlarge intestine
    66. BNchitin,
    67. BOnitrogen
    68. BPsecond
  5. 5Lipids are [blank_start]hydrophobic[blank_end] molecules composed of carbon, [blank_start]hydrogen[blank_end], and oxygen. They are a varied group of molecules that contain fewer [blank_start]polar[blank_end] O–H bonds and more non-polar [blank_start]C–H[blank_end] bonds than do carbohydrates. Thus, they are [blank_start]insoluble[blank_end] in water but soluble in other nonpolar substances. Some are large molecules consisting of long hydrocarbon chains attached to smaller polar subunits, while others are compact molecules consisting of several [blank_start]hydrocarbon rings[blank_end]. Organisms use lipids for [blank_start]storing energy[blank_end], building [blank_start]membranes[blank_end], and other cell parts, and as chemical [blank_start]signaling[blank_end] molecules. Lipids can be divided into four families: [blank_start]fats[blank_end], [blank_start]phospholipids[blank_end], [blank_start]steroids[blank_end], and [blank_start]waxes[blank_end].Fats are the most common energy-storing molecules in living organisms. A gram of fat stores about 38 kJ (9 kilocalories) of chemical energy per gram, more than twice the 17 kJ (4 kilocalories) of chemical energy stored in a gram of carbohydrate or protein. A calorie is a non-SI unit for energy that is commonly used in the food industry and in food science. One calorie (cal) is equal to 4.18 J. One kilocalorie, symbolized 1 kcal, 1 Calorie, or 1 Cal on food labels, is equivalent to 4.18 kJ. Animals convert excess [blank_start]carbohydrates[blank_end] into fat and store the fat molecules as droplets in the cells of [blank_start]adipose[blank_end] (fat) tissue. A layer of fat under the skin acts as [blank_start]thermal insulation[blank_end] in many animals, such as penguins (Figure 15). Plants also store energy in the form of fat. The most common fats in plants and animals are the [blank_start]triacylglycerols (triglycerides)[blank_end]. These contain [blank_start]three[blank_end] fatty acids attached to a single molecule of [blank_start]glycerol[blank_end]. Glycerol is [blank_start]three[blank_end]-carbon alcohol containing a [blank_start]hydroxyl[blank_end] group attached to each carbon. Fatty acids are long hydrocarbon chains containing a [blank_start]single carboxyl[blank_end] group (COOH) at one [blank_start]end.[blank_end] The hydrocarbon chains are usually even-numbered and 16 or 18 carbon atoms long. Saturated fatty acids have only [blank_start]single bonds[blank_end] between carbon atoms. Unsaturated fatty acids, such as oleic acid, have one or more carbon-carbon [blank_start]double[blank_end] bonds. Saturated fatty acids are saturated because they contain the maximum number of hydrogen atoms possible attached to the carbon skeleton. Unsaturated fatty acids have fewer than the maximum number of [blank_start]hydrogens[blank_end] possible. The double bonds between carbons are formed by [blank_start]removing[blank_end] hydrogen atoms from the molecule. Fatty acids with many carbon-carbon double bonds are called [blank_start]polyunsaturated[blank_end] fatty acids. Animal fats, such as butter and lard, are mostly composed of triacylglycerols containing only [blank_start]saturated[blank_end] fatty acids. The [blank_start]straight[blank_end] hydrocarbon chains of the fatty acids fit [blank_start]closely together[blank_end], allowing for many [blank_start]van der Waals[blank_end] attractions along their length. This results in a [blank_start]solid[blank_end] consistency at room temperature. The unsaturated and polyunsaturated fatty acids are [blank_start]bent[blank_end] at the double bonds. These rigid kinks in the fatty acid tails [blank_start]reduce[blank_end] the number of van der Waals attractions that can form along their lengths, causing oils to be [blank_start]liquids[blank_end] at room temperature. An industrial process called [blank_start]hydrogenation[blank_end] adds hydrogen atoms to the double bonds in unsaturated triacylglycerols of liquid fats, such as corn oil or canola oil, converting them into a semisolid material, such as margarine or shortening. When glycerol reacts with fatty acids, a [blank_start]condensation[blank_end] reaction takes place between a [blank_start]hydroxyl[blank_end] group of glycerol and the carboxyl group of a [blank_start]fatty acid[blank_end]. The resulting bond is called an [blank_start]ester linkage[blank_end], and the process is known as esterification. The membranes of cells are mostly composed of fats called [blank_start]phospholipids[blank_end]. Phospholipids are composed of a [blank_start]glycerol[blank_end] molecule to which is attached [blank_start]two[blank_end] fatty acids and a highly polar [blank_start]phosphate group[blank_end]. The phosphate group can be thought of as a polar [blank_start]head[blank_end] and the fatty acids as long, [blank_start]nonpolar[blank_end] tails. The polar head is [blank_start]hydrophilic[blank_end] and the nonpolar tails are [blank_start]hydrophobic[blank_end]. When added to water, phospholipids form spheres, called [blank_start]micelles[blank_end]. The hydrophilic heads dissolve in the water and their hydrophobic tails mix with one another in the center of the sphere. Cell membranes normally separate two water compartments, such as [blank_start]extracellular fluid[blank_end] and the cell’s cytoplasm. A [blank_start]double[blank_end] layer of phospholipids allows for heads to mix with water in both compartments and tails to mix with one another in the [blank_start]center[blank_end] of the bilayer. Water and other [blank_start]polar and ionic[blank_end] materials cannot pass through the bilayer because of the highly [blank_start]nonpolar[blank_end] center. Functional cell membranes contain proteins and [blank_start]hydrophilic pores[blank_end] that form channels through which charged materials can pass. Membranes often contain another class of lipid called [blank_start]sterols[blank_end]. Sterols (also called steroids) are compact hydrophobic molecules containing four fused [blank_start]hydrocarbon rings[blank_end] and several different functional groups. Cholesterol is an important [blank_start]steroid[blank_end] component of cell membranes. High concentrations of cholesterol in the bloodstream and a diet rich in saturated fats have been linked to the development of atherosclerosis, a condition in which fatty deposits, called [blank_start]plaque[blank_end], form on the inner lining of blood vessels, blocking the flow of [blank_start]blood[blank_end] to tissues. Deprived of oxygen and nutrients, the cells of the tissues die. If the tissue happens to be heart muscle, a heart attack may occur. If blood flow to the brain is blocked, the person may suffer a stroke, possibly leading to paralysis and loss of bodily functions. Cells convert cholesterol into a number of compounds, such as [blank_start]vitamin D[blank_end] (needed for healthy bones and teeth) and bile salts (needed for the digestion of fats in the small intestines). Other steroids include the sex hormone [blank_start]testosterone,[blank_end] estrogens, and progesterone—that control the development of sex traits and gametes. [blank_start]Waxes[blank_end] are lipids containing long-chain fatty acids linked to [blank_start]alcohol or carbon rings[blank_end]. They are hydrophobic molecules with a firm, pliable consistency. This property makes waxes ideally suited to form waterproof coatings on various plant and animal parts. A type of wax called cutin is produced by the epidermal cells of plants, forming a water-resistant coating on the surfaces of stems, leaves, and fruit. This helps the plant conserve water and also acts as a barrier to infection. Birds secrete a waxy material that helps keep their [blank_start]feathers[blank_end] dry, and bees produce [blank_start]beeswax[blank_end] to construct honeycombs.
    1. Ahydrophobic
    2. Bhydrogen
    3. Cpolar
    4. DC–H
    5. Einsoluble
    6. Fhydrocarbon rings
    7. Gstoring energy
    8. Hmembranes
    9. Isignaling
    10. Jwaxes
    11. Ksteroids
    12. Lphospholipids
    13. Mfats
    14. Ncarbohydrates
    15. Oadipose
    16. Pthermal insulation
    17. Qtriacylglycerols (triglycerides)
    18. Rglycerol
    19. Sthree
    20. Tthree
    21. Uhydroxyl
    22. Vsingle carboxyl
    23. Wend.
    24. Xsingle bonds
    25. Ydouble
    26. Zhydrogens
    27. AAremoving
    28. ABpolyunsaturated
    29. ACsaturated
    30. ADstraight
    31. AEclosely together
    32. AFvan der Waals
    33. AGsolid
    34. AHbent
    35. AIreduce
    36. AJliquids
    37. AKhydrogenation
    38. ALcondensation
    39. AMhydroxyl
    40. ANfatty acid
    41. AOester linkage
    42. APphospholipids
    43. AQglycerol
    44. ARtwo
    45. ASphosphate group
    46. AThead
    47. AUnonpolar
    48. AVhydrophilic
    49. AWhydrophobic
    50. AXmicelles
    51. AYextracellular fluid
    52. AZdouble
    53. BAcenter
    54. BBpolar and ionic
    55. BCnonpolar
    56. BDhydrophilic pores
    57. BEsterols
    58. BFhydrocarbon rings
    59. BGsteroid
    60. BHplaque
    61. BIvitamin D
    62. BJtestosterone,
    63. BKWaxes
    64. BLalcohol or carbon rings
    65. BMfeathers
    66. BNbeeswax
    67. BOblood
  6. 6The genetic information in DNA codes specifically for the production of [blank_start]proteins[blank_end] and nothing else. Proteins accomplish more tasks than any other group of biological molecules, and they make up more than [blank_start]50%[blank_end] of the dry mass of most cells. They are used as [blank_start]structural building blocks[blank_end] and, as functional molecules, are involved in almost everything that [blank_start]cells[blank_end] do. Cells contain thousands of different proteins, each performing a specific task. As with carbohydrates and lipids, their three-dimensional structure is
    directly related to their [blank_start]function[blank_end]. Proteins called enzymes act as biological [blank_start]catalysts,[blank_end] making chemical reactions proceed at a speed that sustains life. Proteins called [blank_start]immunoglobulins[blank_end] to protect animals against foreign microbes and [blank_start]cancer[blank_end] cells. A variety of protein molecules help to trans-
    port materials through [blank_start]cell membranes[blank_end] and through the bodies of plants and animals. Hemoglobin shuttles [blank_start]oxygen[blank_end] from place to place in mammals and protein carriers help move sucrose through phloem tissue in plants. [blank_start]Keratin[blank_end], the most common protein in vertebrates, is a tough, structural protein found in hair and fingernails. Fibrin is the protein that helps [blank_start]blood clot[blank_end], and collagen forms the protein component of bones, skin, ligaments, and tendons. Proteins are [blank_start]amino acid[blank_end] polymers folded into specific three-dimensional shapes. A protein’s [blank_start]structural[blank_end] characteristics determine its function. An amino acid is an organic molecule possessing a central [blank_start]carbon atom[blank_end] to which are attached to an amino group, a carboxyl group, a [blank_start]hydrogen[blank_end] atom, and a variable group of atoms called a side chain, usually symbolized by the letter [blank_start]R[blank_end]. There are 20 different R groups commonly found in living organisms and, therefore, 20 different amino acids. Glycine (Gly) is the simplest amino acid, with a [blank_start]single[blank_end] hydrogen atom as its R group.
    Notice that the amino and carboxyl groups are ionized. Amino acids are [blank_start]amphiprotic[blank_end], which means that they possess both acidic (carboxyl) and basic (amino) functional groups. When dissolved in water, the carboxyl group donates an [blank_start]H[blank_end] ion to the amino group, causing the carboxyl group to become [blank_start]negatively[blank_end] charged and the amino group to possess extra hydrogen and a net [blank_start]positive[blank_end] charge. Amino acids may be polar (hydrophilic), nonpolar (hydrophobic), or charged (acidic or basic), depending on the
    nature of their [blank_start]side chains[blank_end]. Proline (pro) is the only amino acid whose side chain forms a covalent bond with its own amino group. Acidic amino acids possess a carboxyl group on their side chains, and basic amino acids contain [blank_start]amino[blank_end] groups on their side chains. Proteins consist of one or more amino acid polymers that have twisted and coiled into a specific shape. The final shape, or conformation, of the polymer, is determined by
    the [blank_start]sequence[blank_end] of amino acids it contains. An amino acid polymer is called a [blank_start]polypeptide[blank_end]. Polypeptides are constructed in the cytoplasm of cells through a complex process called protein synthesis. Multiple copies of each of the 20 amino acids are dissolved in the [blank_start]cytoplasm[blank_end] of all cells. These are constructed by the cell from simpler compounds or obtained in the diet from proteins, in food, that the organism absorbs and digests. Of the 20 amino acids found in the food humans normally eat, [blank_start]8[blank_end] are considered to be essential amino acids. This means that the body [blank_start]cannot[blank_end] synthesize them
    from simpler compounds; they must be obtained from the [blank_start]diet.[blank_end] The 8 essential amino acids are tryptophan, methionine, valine, threonine, phenylalanine, leucine, isoleucine, and lysine. In protein synthesis, genetic information contained in [blank_start]DNA[blank_end] (sometimes RNA), directs ribosomes, RNA, and enzymes to join amino acids to one another in a
    particular sequence. The bonds that hold the amino acids together are called [blank_start]peptides[blank_end] bonds. Peptide bonds are formed by a [blank_start]condensation[blank_end] reaction between the [blank_start]amino[blank_end] group of one amino acid and the [blank_start]carboxyl[blank_end] group of adjacent amino acids. This type of functional group linkage is called an a[blank_start]mide[blank_end] bond. The polypeptide chain will always have an amino group at one end, called the [blank_start]amino terminus[blank_end] (A-terminus), and a carboxyl group at the other, called the [blank_start]carboxyl terminus[blank_end] (C-terminus). Polypeptides range in length from a few amino acids to more than a thousand. All copies of a particular polypeptide have the same sequence of amino acids, this
    the sequence is coded for by a particular [blank_start]gene[blank_end] in a DNA molecule. The sequence of amino acids determines a polypeptide’s three-dimensional conformation and, thus, its functional characteristics. Many structural proteins are roughly linear in shape and arranged to form strands or sheets. Globular proteins are composed of one or more polypeptide chains that take on a [blank_start]rounded, spherical shape[blank_end]. Many enzymes and other functional proteins are [blank_start]globular[blank_end]. Globular proteins may be described in terms of four levels of structure: primary, secondary, tertiary, and quaternary. The first three structures—primary, secondary, and tertiary—apply to the individual polypeptide chains of a protein, while the fourth, [blank_start]quaternary structure,[blank_end] describes the interactions that occur between polypeptide strands in proteins composed of two or more polypeptides. The primary structure is the unique sequence of amino acids in a polypeptide chain. Each of the amino acids in a polypeptide is referred to as a [blank_start]residue[blank_end]. [blank_start]Fredrick Sanger[blank_end], a British biochemist, was the first to determine the primary structure
    of a protein. He received the Nobel Prize in 1958 for determining the sequence of the 51 amino acids in the protein hormone [blank_start]insulin[blank_end]. When Sanger announced that he wanted to determine the sequence of amino acids in a naturally occurring protein, his professor said that he was mad! Sanger received another Nobel Prize in 1980 for his work on gene
    structure. The primary structure is determined by the [blank_start]nucleotide[blank_end] sequence in a gene in DNA. During protein synthesis (discussed further in Chapter 5), the nucleotide sequence governs the [blank_start]order[blank_end] in which individual amino acids are linked to form the polypeptide chains that fold into functional protein molecules. With 20 different amino acids to choose from, a polypeptide containing 200 amino acids could be arranged into 20200 different sequences more than all the atoms in the known universe! The final confirmation of a protein is very [blank_start]sensitive[blank_end] to the primary structure. Changing the sequence by one amino acid could alter the three-dimensional shape to the point that the protein [blank_start]loses[blank_end] function or is rendered [blank_start]useless[blank_end]. This happens in sickle cell anemia, an inherited condition in which a single amino acid substitution changes the conformation of a polypeptide in hemoglobin, causing red blood cells to become deformed. The deformed cells clog blood vessels and impede blood flow to the tissues. During protein synthesis, amino acids are added to the growing chain one at a time. As
    the chain grows, it coils and folds at various locations along its length. These coils and folds are collectively referred to as the polypeptide’s [blank_start]secondary[blank_end] structure. In certain regions, a hydrogen bond forms between the electronegative oxygen of the carboxyl group (CO) of one peptide bond and the electropositive hydrogen of an amino group (N–H) four peptide bonds away. These H bonds, repeated over a certain length of the chain, shape
    portions of the polypeptide into a coil called a [blank_start]helix[blank_end]. Fibrous proteins, such as -keratin, the protein in hair, are almost completely shaped into a helix.
    Many globular proteins, such as lysozyme, an enzyme that acts as a natural disinfectant in saliva, sweat, and tears, have regions of helix separated by nonhelical regions called -pleated sheets. This type of secondary structure occurs when two parts of the polypeptide chain lie [blank_start]parallel[blank_end] to one another. In this case, hydrogen bonds form between the oxygen atoms of carboxyl
    groups on one strand and the hydrogen atoms of amino groups on an adjacent strand. Some fibrous proteins, such as the protein in
    the silk that spiders use to construct their webs contains large amounts of -pleated sheets. When building their webs, spiders secrete silk fibers in liquid form. These [blank_start]solidify[blank_end] when exposed to air. The hydrogen bonds that
    form in the many regions of -pleated sheets make the silk stronger than steel (spider silk can be stretched about 40% before it breaks; steel can only be stretched by about 8%). Strong forces of attraction and repulsion between the polypeptide and its environment force it to undergo additional folding into a [blank_start]tertiary[blank_end] structure. Amino acids containing polar R groups, such as serine, tyrosine, and glutamine, are attracted to water, while those containing nonpolar R groups are excluded. As a result, amino acids with hydrophobic groups, such as valine and phenylalanine, [blank_start]congregate[blank_end] in
    the interior of the folded polypeptide, away from water. Tertiary structure is stabilized by a number of different R-group interactions. Hydrogen bonds between certain polar side chains, ionic bonds between oppositely charged side chains, and van der Waals forces between nonpolar R groups, all help to keep the polypeptide folded into a tertiary structure. Proline, the only amino acid in which the R group is attached to the amino group, forms
    a natural kink where it occurs in a helix or [blank_start]a -pleated sheet[blank_end]. This also helps shape a tertiary structure. Whenever the sulfur-containing R groups of two [blank_start]cysteine[blank_end] residues are brought close to one another, a covalent bond called a [blank_start]disulfide bridge[blank_end] (-S-S-) may form. Disulfide bridges are strong stabilizers of tertiary structure. In some cases, two or more polypeptide subunits must come together to form a functional protein. Such proteins are said to be in the quaternary structure. Collagen (the tough fibrous protein found in skin, bones, tendons, and ligaments), keratin (the fibrous protein in hair), and hemoglobin, the globular protein that transports oxygen in red blood cells are examples of proteins in quaternary structure. Hemoglobin is composed of four polypeptides in tertiary structure: two identical -chains and two identical -chains. Each subunit has a nonproteinaceous heme group containing an [blank_start]iron[blank_end] atom that binds oxygen. It is evident that a polypeptide’s final shape, its tertiary structure, is determined by
    its primary structure. However, chemical and physical environmental factors also help to determine the final shape of the molecule. Within a cell, a protein is constructed in an aqueous environment at a neutral pH and a particular temperature. If a protein produced in this environment is placed in different environmental conditions, it may unravel. A change in the three-dimensional shape of a protein caused by changes in [blank_start]temperature[blank_end], pH, ionic [blank_start]concentration[blank_end], or other environmental factors is called [blank_start]denaturation[blank_end].
    A denatured protein cannot [blank_start]carry[blank_end] out its biological [blank_start]functions[blank_end]. Various chemicals and heat disrupt the hydrogen bonds, ionic bonds, disulfide bridges, and hydrophobic interactions that help hold a polypeptide in tertiary structure. A protein denatured by [blank_start]heat[blank_end] or [blank_start]chemicals[blank_end] will usually return to its normal shape when the denaturing agent is removed, as long as its primary structure remains intact. If the denaturing agent breaks the peptide bonds that hold the amino acids together, the protein will be [blank_start]destroyed[blank_end]. Protein denaturation can be both dangerous and useful. Protein enzymes function best within a [blank_start]narrow[blank_end] range of temperature, pH, and salt concentration. Enzymes in [blank_start]thermophiles[blank_end] (archaebacteria that normally live in water at temperatures around 100°C) can not survive at room temperature because their proteins and enzymes would denature. Gastrin, a digestive enzyme in the stomach, works best at pH 2 and is denatured in
    the small intestine, where the pH increases to about 10. Prolonged fever above 39°C could denature critical enzymes in the brain, leading to seizures and possibly death. Curing meats with high concentrations of salt or sugar, and pickling meat or vegetables in vinegar, preserves the food by denaturing the enzymes in bacteria that would other-
    wise spoil the food. The practice of blanching fruits and vegetables by quickly dipping them in boiling water denatures enzymes that would otherwise cause them to turn brown when exposed to air. Heat can be used to denature the proteins in hair, allowing people to temporarily straighten curly hair or curl straight hair. In general, small proteins are able to [blank_start]refold[blank_end] into the [blank_start]tertiary[blank_end] structure once the [blank_start]denaturing[blank_end] [blank_start]agent[blank_end] is removed; however, large globular proteins [blank_start]fail[blank_end] to refold spontaneously because many [blank_start]intricate folds[blank_end] are needed to reestablish tertiary structure. In fact, recent research
    into how proteins fold when they are created in protein synthesis has revealed that special proteins, called [blank_start]chaperone[blank_end] proteins, aid the growing polypeptide to fold into a tertiary structure. Some forms of cystic fibrosis, a genetic disease characterized by the inability of certain proteins to move ions across cell membranes, are caused by a deformation in the proteins’ three-dimensional structure. Protein sequencing studies have shown that the affected proteins possess the same [blank_start]primary[blank_end] structure as normal proteins of the same type, causing researchers to speculate that the proteins fail to fold because of a deficiency in specific chaperone proteins.
    Humans consume animal flesh (meat) as a source of protein. However, the fibrous proteins contained in muscle cells, the most common type of meat, make raw meat difficult to chew. The heating denatures the fibrous protein molecules and partially decomposes them. In many cases, the primary purpose of cooking is to denature the protein component of food. Foods are usually a rich mixture of nutrients including carbohydrates, lipids, proteins, nucleic acids, vitamins, and minerals. The [blank_start]hydrolysis reaction[blank_end] separates glycine, alanine, and threonine units in a [blank_start]1:2:1[blank_end] molecular ratio. However, information regarding the sequence is lost as the individual molecules randomly mix in the solution. The amino-terminal residue of a polypeptide (glycine in this case) can be identified by first attaching a “flag” molecule to this residue while the peptide is intact. Then, the modified residue from the polypeptide is removed by [blank_start]hydrolyzing[blank_end] the entire polymer and isolating and purifying the modified amino-terminal amino acid. Unfortunately, the need to hydrolyze the amino-terminal amino acid (to isolate, purify, and identify it) hydrolyzes the other peptide bonds as well, destroying the rest of the
    [blank_start]sequence. In 1947, Pehr Victor[blank_end] Edman, working at the Rockefeller Institute in Princeton, New Jersey, discovered that a substance called phenylisothiocyanate (PITC) (Figure 37) could bind to the amino terminus and weaken the adjacent peptide bond. When the polypeptide
    is subjected to trifluoroacetic acid (Figure 38), the modified amino-terminal amino acid breaks off, leaving the rest of the polypeptide intact. The modified amino-terminal amino acid, now called a phenylthiohydantoin (PTH) derivative, is separated from the rest of the polypeptide, purified, and identified. The procedure is repeated with the rest of the polypeptide, resulting in the determination of the peptide sequence This process has been fully automated and can be used with extremely small quantities of polypeptide or protein in the picomole (1012 mol) range. These procedures are frequently referred to as “wet” methods because they are done in a solution. Although precise, the method begins to fail after about 20 to 40 residues have been determined, so that it is necessary to break proteins into [blank_start]smaller[blank_end] pieces before beginning the process. The Edman degradation is then used to sequence the smaller fragments of the original chain.
    Although the amino acid sequences of the fragments are obtained, the order in which these smaller segments occur in the original protein is lost. To determine the overall sequence of original peptides, the original polypeptide must be cleaved by enzymes that are known to hydrolyze a particular peptide bond. Using two such enzymes (each cleaving
    the original polypeptide into different pieces), performing an Edman degradation on each fragment, and comparing the results allows the sequence of the original polypeptide to be determined. Today, automated sequencers carry out complete Edman degradations on polypeptides containing tens of amino acids in less than one day.
    1. Aproteins
    2. B50%
    3. Ccells
    4. Dstructural building blocks
    5. Efunction
    6. Fcatalysts,
    7. Gimmunoglobulins
    8. Hcancer
    9. Icell membranes
    10. Joxygen
    11. KKeratin
    12. Lblood clot
    13. Mamino acid
    14. Nstructural
    15. OR
    16. Pcarbon atom
    17. Qhydrogen
    18. Rsingle
    19. Samphiprotic
    20. TH
    21. Unegatively
    22. Vpositive
    23. Wside chains
    24. Xamino
    25. Ypolypeptide
    26. Zsequence
    27. AAcytoplasm
    28. AB8
    29. ACcannot
    30. ADdiet.
    31. AEDNA
    32. AFpeptides
    33. AGcondensation
    34. AHmide
    35. AIamino
    36. AJcarboxyl
    37. AKcarboxyl terminus
    38. ALamino terminus
    39. AMgene
    40. ANrounded, spherical shape
    41. AOglobular
    42. APresidue
    43. AQFredrick Sanger
    44. ARinsulin
    45. ASnucleotide
    46. ATorder
    47. AUsensitive
    48. AVloses
    49. AWuseless
    50. AXsecondary
    51. AYhelix
    52. AZparallel
    53. BAtertiary
    54. BBsolidify
    55. BCquaternary structure,
    56. BDcongregate
    57. BEa -pleated sheet
    58. BFcysteine
    59. BGdisulfide bridge
    60. BHiron
    61. BItemperature
    62. BJconcentration
    63. BKdenaturation
    64. BLfunctions
    65. BMcarry
    66. BNheat
    67. BOchemicals
    68. BPdestroyed
    69. BQnarrow
    70. BRthermophiles
    71. BSrefold
    72. BTtertiary
    73. BUdenaturing
    74. BVagent
    75. BWfail
    76. BXintricate folds
    77. BYchaperone
    78. BZprimary
    79. CAhydrolysis reaction
    80. CB1:2:1
    81. CChydrolyzing
    82. CDsequence. In 1947, Pehr Victor
    83. CEsmaller
  7. 7Nucleic acids are informational macromolecules. They are used by all organisms to store [blank_start]hereditary[blank_end] information that determines structural and functional characteristics. They are the only molecules in existence that can produce [blank_start]identical copies of themselves[blank_end], and in so doing, allow organisms to [blank_start]reproduce[blank_end]. The instructions for creating an organism are stored in digital code along coiled chains of [blank_start]deoxyribonucleic acid,[blank_end] referred to as DNA.
    Another nucleic acid, [blank_start]ribonucleic acid, RNA[blank_end], reads the information in DNA and transports it to the protein-building apparatus of the cell. Here, the instructions direct the production of structural and functional proteins. DNA and RNA are nucleotide [blank_start]polymers[blank_end]. A nucleotide subunit in both molecules contains a [blank_start]nitrogenous base[blank_end], a five-carbon (pentose) sugar, and a [blank_start]phosphate group[blank_end]. DNA contains the sugar [blank_start]deoxyribose[blank_end], whereas [blank_start]RNA[blank_end] contains ribose. The only difference between these two monosaccharides is the lack of an [blank_start]oxygen[blank_end] atom at carbon [blank_start]2[blank_end] in deoxyribose, which accounts for its name. There are five types of organic bases found in nucleic acids: [blank_start]adenine[blank_end] (A), [blank_start]guanine[blank_end] (G), [blank_start]cytosine[blank_end] (C), [blank_start]thymine[blank_end] (T), and uracil, (U). Cytosine, thymine, and uracil are single ringed [blank_start]pyrimidines[blank_end], while adenine and guanine are larger double-ringed [blank_start]purines[blank_end]. DNA has nucleotides containing the bases A, G, C, and T, while RNA contains A, G, and C, and U instead of T. Notice the structural similarity between [blank_start]U[blank_end] and [blank_start]T.[blank_end] When a DNA or RNA molecule is built, specific enzymes link a series of nucleotides to one
    another forming a polymer called a [blank_start]strand[blank_end]. The [blank_start]enzymes[blank_end] facilitate the formation of covalent bonds between the phosphate group of one nucleotide and the hydroxyl group attached to the number [blank_start]3[blank_end] carbon of the sugar on the adjacent nucleotide. A phosphodiester bond forms as the result of a condensation reaction between two [blank_start]OH[blank_end] groups.RNA molecules coil into a helix but remain [blank_start]single[blank_end]-stranded.DNA molecules are also helical in structure, but they are composed of [blank_start]two[blank_end] DNA strands wound around each other like the inside and outside rails of a circular staircase. The two strands in DNA are held together by [blank_start]hydrogen bonds[blank_end] between nitrogenous bases on adjacent strands. There is a strict rule regarding base pairing. Adenine (A) always bonds to [blank_start]thymine (T)[blank_end] with two hydrogen bonds; [blank_start]guanine (G)[blank_end] always
    bonds to cytosine (C) with three hydrogen bonds. Each strand of the DNA molecule has a free [blank_start]phosphate[blank_end] group at one end and a free sugar (deoxyribose) at the other end. Hydrogen bonds will form properly only if one strand is upside down compared with the other strand. This means that the free phosphate end of one strand lines up with the free sugar end of the adjacent strand. Because of this, the two strands are said to run [blank_start]antiparallel.[blank_end] Every nucleotide pair is composed of a purine (double ring) facing a pyrimidine (single ring). Nucleotides are not only used in the construction of DNA and RNA, they are also important intermediates in a cell’s [blank_start]energy[blank_end] transformations. The nucleotide [blank_start]adenosine triphosphate (ATP)[blank_end] is used to drive virtually all the energy-requiring reactions in a cell. Nucleotide derivatives, such as nicotinamide adenine dinucleotide (NAD) and flavin
    adenine dinucleotide (FAD), are used in the production of ATP. NADP, a nucleotide similar to NAD, is used as a coenzyme in photosynthesis and cyclic adenosine monophosphate (cAMP) is used as a “second messenger” in various hormone interactions. All organisms pass on to their [blank_start]offspring[blank_end] their unique sequence of nucleotides in DNA. According to the theory of evolution, organisms possessing similar features are more closely related than those sharing fewer features. Thus, humans seem to be more closely
    related to apes than they are to crickets. But are we more related to gorillas than we are to gibbons? A smaller number of anatomical differences may produce inconclusive results. New studies comparing the sequence of nucleotides in DNA are beginning to yield more convincing evidence of evolutionary kinship. It is hypothesized that more closely related organisms contain more closely related [blank_start]sequences[blank_end] of nucleotides in their DNA molecules. In nucleic acid hybridization studies, researchers force the DNA molecules from two different organisms to unwind and separate into individual strands by breaking the hydrogen bonds between them. They allow the separated strands from one organism to mix with the
    separated strands of the other organism. As the strands mingle, complementary bases will attach to one another with hydrogen bonds, forming hybrid DNA molecules. Heating the [blank_start]hybrid[blank_end] molecules and measuring the amount of heat needed to break the hydrogen bonds
    and separate the strands provides a measure of the similarity in nucleotide sequence between the strands. More heat will be required to separate the hybrid DNA molecules of [blank_start]more closely[blank_end] related species because these combinations will produce more base pairs.

    - The nitrogenous base can be a single ring (solid lines) or a double ring (dotted lines) structure.
    - In DNA, the sugar is deoxyribose; in RNA, it is ribose.

    - There are five types of nitrogenous bases: adenine (A), guanine (G), cytosine (C), thymine (T), and uracil (U). C, T, and U are pyrimidines composed of a single ring, while A and G are purines composed of a double ring. DNA contains A, G, C, and T. Like DNA, RNA contains A, G, and C but contains U instead of T. Notice the structural similarity between [blank_start]U[blank_end] and T.

    - Nucleotides are attached to one another by a [blank_start]phosphodiester[blank_end] linkage between the phosphate group of one nucleotide and the sugar of the next.

    This forms a single strand of DNA or RNA. RNA molecules remain [blank_start]single-[blank_end]stranded. DNA molecules are double-stranded. The two strands in DNA are held together by hydrogen bonds that form between a nitrogenous base on one strand and a complementary base on the adjacent strand. Notice how the two strands run antiparallel—one strand being upside down compared with the other strand—and how every nucleotide pair is composed of a purine (double ring) facing a pyrimidine (single ring). Also, note that thymine (T) is always attached to adenine (A) by [blank_start]two[blank_end] hydrogen bonds and cytosine (C) to guanine (C) by [blank_start]three[blank_end] hydrogen bonds.

    • A condensation reaction links the subunits of macromolecules together. A water molecule is formed in the process. Hydrolysis reactions use water molecules to [blank_start]break[blank_end] macromolecules into their constituent subunits.

    • Carbohydrates contain carbon, hydrogen, and oxygen atoms in a 1:2:1 ratio. Monosaccharides are simple sugars. Oligosaccharides are monosaccharide polymers containing two or three simple sugars. Polysaccharides are polymers composed of several hundred to several thousand monosaccharide subunits held together by [blank_start]glycosidic[blank_end] linkages.

    • Lipids (fats) are hydrophobic molecules composed of carbon, hydrogen, and oxygen. The most common fats are the triacylglycerols (triglycerides) composed of glycerol and three fatty acids. Fatty acids are long hydrocarbon chains containing a single carboxyl group ([blank_start]COOH[blank_end]) at one end. Cholesterol is an important sterol component of cell membranes. Other steroids include the sex hormones testosterone, estrogens, and progesterone. Phospholipids are key components of biological [blank_start]membranes[blank_end].

    • Proteins are amino acid polymers folded into specific [blank_start]three-dimensional[blank_end] shapes. An amino acid is an organic molecule possessing a central carbon atom to which are attached to an amino group, a carboxyl group, a hydrogen atom, and a variable group of atoms called [blank_start]a side chain,[blank_end] usually symbolized by the letter R. A change in the three-dimensional shape of a protein caused by changes in temperature, pH, ionic concentration, or other environmental factors is called denaturation. A denatured protein cannot carry out its biological functions.

    • Nucleic acids are [blank_start]informational[blank_end] macromolecules composed of nucleotide polymers. DNA and RNA are important nucleic acids.    Bild zu Frage 7
    1. Ahereditary
    2. Bidentical copies of themselves
    3. Creproduce
    4. Ddeoxyribonucleic acid,
    5. Epolymers
    6. Fribonucleic acid, RNA
    7. Gnitrogenous base
    8. Hphosphate group
    9. Ideoxyribose
    10. JRNA
    11. Koxygen
    12. L2
    13. Madenine
    14. Nguanine
    15. Ocytosine
    16. Pthymine
    17. Qpurines
    18. Rpyrimidines
    19. SU
    20. TT.
    21. Ustrand
    22. Venzymes
    23. W3
    24. XOH
    25. Ysingle
    26. Ztwo
    27. AAhydrogen bonds
    28. ABthymine (T)
    29. ACguanine (G)
    30. ADphosphate
    31. AEantiparallel.
    32. AFenergy
    33. AGadenosine triphosphate (ATP)
    34. AHoffspring
    35. AIsequences
    36. AJU
    37. AKphosphodiester
    38. ALsingle-
    39. AMhybrid
    40. ANtwo
    41. AOthree
    42. APbreak
    43. AQglycosidic
    44. ARCOOH
    45. ASmore closely
    46. ATmembranes
    47. AUthree-dimensional
    48. AVinformational
    49. AWa side chain,
  8. 8Enzymes are protein catalysts. A catalyst is a substance that [blank_start]speeds up[blank_end] a chemical reaction without being [blank_start]consumed[blank_end] in the process. In catalyzed reactions, the reactants are converted into products faster than they would be without the catalyst, and, at the end of the process, the catalyst is regenerated intact, ready to catalyze the same reaction again. A chemical change takes place when the bonds between reactant molecules break,
    and a rearrangement of atoms creates the bonds between the atoms of product molecules. For this to occur, reactant molecules must collide with enough [blank_start]force[blank_end] and with the correct [blank_start]geometric[blank_end] orientation for bond breaking to occur. Only under these conditions can the transition state be reached and product molecules formed. As mentioned earlier, all reactions, whether [blank_start]endergonic[blank_end] or exergonic, possess an activation energy (EA) barrier
    that must be overcome for reaction to occur. [blank_start]Heat[blank_end] provides the activation
    energy for many reactions. The spark from a spark plug provides the activation energy for the combustion of gasoline in an internal combustion engine. Without the spark, the gasoline–oxygen collisions are ineffective and do not allow the reactants to reach the transition state. Although an increase in temperature increases the rate of most reactions, proteins are denatured at [blank_start]high[blank_end] temperatures and lose their function. This could be devastating for the cell. Therefore, living cells [blank_start]cannot[blank_end] rely on high levels of heat as a source of activation energy. Catalysts allow reactions to proceed at suitable rates at moderate temperatures by [blank_start]reducing[blank_end] the activation energy (EA) barrier. The catalyst does not affect the free energy change (G) of a reaction. It cannot change an endergonic reaction into an exergonic reaction; it can only decrease the potential energy level of the transition state and, thus, allow a greater proportion of colliding reactants to reach the transition state and become products. Catalysts can only speed up reactions that would normally take place anyway. Since a catalyst works by reducing
    the energy of activation, it speeds up forward and reverses reactions equally. Thus, it cannot affect the position of equilibrium, only the speed in which equilibrium is reached. The [blank_start]substrate[blank_end] is the reactant that an enzyme acts on when it catalyzes a chemical reaction. The substrate binds to a particular site on the [blank_start]enzyme[blank_end] to which it is [blank_start]attracted[blank_end]. Enzymes are proteins in [blank_start]tertiary[blank_end] or [blank_start]quaternary[blank_end] structures with complex conformations.
    They are very specific for the substrate to which they bind. In most cases, they will not bind the [blank_start]isomers[blank_end] of their substrate. The names of enzymes usually end in -ase. Thus, amylase catalyzes the breakdown of amylose into maltose subunits, and maltase catalyzes the breakdown of maltose into individual glucose molecules. An enzyme-catalyzed reaction is usually written with the name of the enzyme over the arrow.
    Notice that reactions are [blank_start]reversible.[blank_end] In an enzyme-catalyzed reaction, the substrate binds to a very small portion of the enzyme. The location where the substrate binds to the enzyme is called the [blank_start]active[blank_end] site and is usually a pocket or groove in the three-dimensional structure of the protein. The substrate and the active site must possess compatible shapes for binding to occur. As the substrate enters the active site, its functional groups come close to the functional groups of a number of [blank_start]amino acids.[blank_end] The interactions between these chemical groups cause the protein to change its [blank_start]shape[blank_end], thereby better accommodating the substrate. This is known as the induced-fit model of enzyme-substrate interaction. The attachment of the substrate
    to the enzyme’s active site creates the [blank_start]enzyme-substrate complex[blank_end]. e active site and forms weak bonds while the enzyme’s conformation changes to better accommodate the substrate (induced fit). The recycling of enzyme molecules causes [blank_start]cells[blank_end] to catalyze many reactions with relatively small numbers of enzymes. Enzymes, such as maltase, decrease the energy of activation by stretching and bending chemical bonds that normally break in the reaction. Heat energy provided by the cell’s [blank_start]internal environment[blank_end] and the action of the enzyme brings the substrate molecule to the transition state. In other cases, the active site may provide an [blank_start]acidic[blank_end] environment in an otherwise neutral part of the cell. Acidic R groups may be prevalent in the area of the active site. This may provide the low pH environment needed for certain reactions to take place. Enzyme-catalyzed reactions can be [blank_start]saturated[blank_end]. There are a limited number of specific enzyme molecules in a cell at any one time. Since it takes some time for a catalyst to catalyze a particular reaction, the speed at which a catalyzed reaction proceeds cannot
    increase indefinitely by increasing the [blank_start]concentration[blank_end] of the substrate. Temperature and pH affect enzyme activity. As with all other reactions, enzyme-catalyzed reactions increase in speed with an increase in temperature. However, as the temperature increases beyond a critical point, [blank_start]thermal agitation[blank_end] begins to disrupt protein structure, resulting in denaturation and loss of enzyme function. Every enzyme has an optimal [blank_start]temperature[blank_end] at which it works best. Enzyme activity decreases above and below the optimal temperature. Most human enzymes work
    best at around [blank_start]37°C,[blank_end] normal body temperature. There are enzymes in certain species of archaebacteria that work best at or above 100°C. Enzymes also have an optimal pH in which they work best, as Figure 5(b) shows. The digestive enzyme [blank_start]pepsin[blank_end] works best in the acidic environment of the stomach, pH 2. The digestive enzyme trypsin has an optimal pH of 8 and works best in the alkaline environment of the small intestine. Some enzymes require either nonprotein cofactors, such as inorganic substances or organic coenzymes, before they can work properly. These may bind to the active site with covalent bonds, or they may bind weakly with the substrate. Cofactors include zinc ions (Zn2) and manganese ions (Mn2). Coenzymes include the derivatives of many [blank_start]vitamins[blank_end]. One of the most important coenzymes is nicotinamide adenine dinucleotide (NAD),a derivative of vitamin B3 (niacin). This substance acts as an electron carrier in cellular respiration. A similar compound called nicotinamide adenine dinucleotide phosphate (NADP) performs a similar role in photosynthesis. Many coenzymes shuttle molecules from one enzyme to another. Their activities will be discussed further in Chapter 2. A variety of substances inhibit enzyme activity. Competitive inhibitors are so similar
    to the enzyme’s substrate that they are able to enter the enzyme’s active site and block the normal substrate from binding. This process is [blank_start]reversible[blank_end]
    and can be overcome by increasing the [blank_start]concentration[blank_end] of the enzyme’s substrate, allowing it to compete favorably with the inhibitor. Noncompetitive inhibitors differ from competitive types. They do not compete with an enzyme’s substrate for the active site. Instead, they attach to another site on the enzyme, causing a change in the enzyme’s
    [blank_start]shape[blank_end]. This changes the active site in such a way that it loses
    affinity for its substrate. Alternatively, the inhibitor may affect those parts of the active site that perform the work of catalysis, resulting in a [blank_start]loss[blank_end] of enzyme activity. An example is DDT, a poison that inhibits enzymes of the nervous system. However, not all enzyme inhibitors are poisons; some are used by the cell to control enzyme activity. Cells must control enzyme activity to coordinate [blank_start]cellular[blank_end] activities. They may accomplish this in two ways: by restricting the production of a particular enzyme, or by inhibiting
    the action of an enzyme that has already been produced. Some enzymes possess receptor sites, called [blank_start]allosteric sites,[blank_end] that are some distance away from the active site. Substances that bind to the allosteric sites may inhibit or stimulate an enzyme’s activity. Allosterically controlled enzymes are usually composed of proteins in a quaternary structure having several subunits, each with an active site. Binding an activator to an allosteric site [blank_start]stabilizes[blank_end] the protein conformation that keeps all of the active sites available to their substrates. Binding an allosteric inhibitor stabilizes the [blank_start]inactive[blank_end] form of the enzyme. Noncompetitive inhibitors attach to the allosteric sites of certain enzymes. The binding of an activator or inhibitor to one allosteric site will affect the activity of all the active sites on the enzyme. Allosteric regulators attach to their sites using weak bonds. [blank_start]Feedback inhibition[blank_end] is a method used by cells to control metabolic pathways involving a series of sequential reactions, each catalyzed by a specific enzyme. In this case, a product formed later in the sequence of reaction steps allosterically inhibits an enzyme that catalyzes a reaction occurring earlier in the process. This effectively reduces the production of the inhibitor, which is, at the same time, a product of the process. The inhibitor binds to the [blank_start]allosteric site[blank_end] of the enzyme using [blank_start]weak[blank_end] bonds. As the product is used up over time, its concentration [blank_start]decreases[blank_end]. This causes the enzyme to be in the active form more often and the production of the inhibitor product [blank_start]increases[blank_end]. As this occurs, inhibition of the enzyme increases again and the production of the inhibitor is reduced once again. Thus, the amount of product is kept tightly controlled by the feedback inhibition process.
    Feedback inhibition is one of the most common control mechanisms used in metabolism. Finally, cells control metabolic processes by [blank_start]restricting[blank_end] the location of enzymes and enzyme complexes to certain locations within the cell. In some cases, enzymes are incorporated into specific [blank_start]membranes[blank_end] or fluid-filled spaces in the cell. Some of the enzymes for cellular respiration are inside the [blank_start]mitochondria,[blank_end] whereas others are dissolved in the
    cell’s cytoplasm. Thus, the rate of the inner mitochondrial reactions can be controlled by restricting the movement into the mitochondrion of intermediates that are formed in the cytoplasm.
    Many enzymes are used in industrial processes and consumer products. One of the largest industrial users of enzymes is the starch-processing industry. Starch from corn, wheat, and other grains is a plentiful carbohydrate resource, consisting of amylose and amylopectin.
    Starch can be converted to glucose syrups by hydrolysis, and the syrups find many applications as sweeteners in foods, such as candy, biscuits, jams and jellies, and pharmaceuticals like cough syrups, tonics, and vitamin preparations. Hydrolysis can be accomplished without enzymes, but this method can generate distasteful flavours and unsightly colours.
    Enzymatic hydrolysis offers a cleaner and more [blank_start]efficient[blank_end] hydrolysis. In a common process, amylase, produced by the bacterium Bacillus licheniformis, hydrolyzes starch to maltose. Then the enzyme glucoamylase, produced by molds such as Aspergillus and Rhizopus, is added to hydrolyze maltose into individual glucose molecules.
    The most frequently used enzymes in the dairy industry are the protein-hydrolyzing enzymes, called [blank_start]proteases[blank_end]. They are most commonly used to coagulate milk for the manufacture of cheese. The cheese industry often uses the term rennet to refer to an enzyme preparation that coagulates milk. Historically, rennet was obtained from the stomach of calves. The primary enzyme obtained from this source is chymosin, which normally
    aids calves in the digestion of milk proteins. Since around 1990, genetic engineering has made it possible to produce chymosin from microbial sources. The gene for chymosin was removed from the DNA of a calf stomach cell and inserted into the DNA of certain bacteria and yeast cells. The microbes reproduce rapidly in large vats containing a nutrient broth and secrete exact copies of calf chymosin. When making cheese, bacteria are added to milk to begin the curdling process. The bacteria feed on the lactose in the milk and produce lactic acid as a waste product. The lactic acid lowers the pH and begins to denature milk proteins. Chymosin is then added to hydrolyze casein, a protein that makes up about 85% of the total protein in milk, causing it to coagulate into semisolid cheese curd. The curd shrinks and separates from a greenish liquid called whey. Whey is removed from the mixture and the curd is further processed according to the type of cheese being produced. Many dairy products are made from cow’s milk. Lactose, a disaccharide composed of glucose and galactose, accounts for 40% of the solids in cow’s milk. Lactose is removed from some milk products because many people are intolerant to it and suffer gastrointestinal distress when exposed to it in their diet. Lactose-intolerant individuals may easily absorb and metabolize glucose and galactose. Lactose is hydrolyzed into [blank_start]glucose[blank_end] and galactose by the enzyme [blank_start]-galactosidase (lactase)[blank_end], which may be obtained from several microorganisms, including Aspergillus niger and Saccharomyces lactis. In addition to causing illness in people who are intolerant, lactose causes severe problems in cheese making. Large quantities of whey are made as a byproduct of cheese production. Whey contains the lactose present in the original milk. Problems arise because
    lactose is not particularly soluble and tends to crystallize out of solution. This leads to an undesirable grainy texture in some cheeses and ice creams. The enzyme -galactosidase produced by S. lactis is used to solve this problem because it is active at 4°C, the temperature at which milk is normally stored. This means that the enzyme can be added to the milk during the overnight cold storage period used in dairies.
    Fat-hydrolyzing enzymes called lipases are used by the dairy industry to develop characteristic cheeses, especially in Italian cheeses and other varieties with strong flavours. Although mozzarella receives most of its flavour from the proteases, lipases produce the strong-flavored cheeses like Romano. These enzymes [blank_start]hydrolyze[blank_end] the fat in milk to produce free fatty acids. The type and concentration of fatty acids give the cheeses their distinct flavours. In addition to the food industry, enzymes are also used in the cleaning industry. Dirt commonly found on clothing includes proteins, starch, and lipids. Although it is possible to remove these stains with soaps and detergents, enzymes allow stains to be removed at [blank_start]lower[blank_end] temperatures and with less mechanical agitation in a washing machine. Enzymes
    are also more effective than nonbiological cleaning agents at removing stains such as blood, grass, milk, and perspiration. The cleaning industry commonly adds proteases and amylases to detergents to help remove protein and carbohydrate stains from clothing and other fabrics.
    1. Aspeeds up
    2. Bconsumed
    3. Cforce
    4. Dgeometric
    5. Eendergonic
    6. FHeat
    7. Gcannot
    8. Hreducing
    9. Isubstrate
    10. Jenzyme
    11. Kattracted
    12. Ltertiary
    13. Mquaternary
    14. Nisomers
    15. Oreversible.
    16. Pactive
    17. Qamino acids.
    18. Rshape
    19. Scells
    20. Tenzyme-substrate complex
    21. Uinternal environment
    22. Vacidic
    23. Wsaturated
    24. Xconcentration
    25. Ythermal agitation
    26. Ztemperature
    27. AA37°C,
    28. ABpepsin
    29. ACvitamins
    30. ADreversible
    31. AEconcentration
    32. AFshape
    33. AGallosteric sites,
    34. AHcellular
    35. AIstabilizes
    36. AJinactive
    37. AKlower
    38. ALhydrolyze
    39. AMweak
    40. ANFeedback inhibition
    41. AOdecreases
    42. APincreases
    43. AQallosteric site
    44. ARloss
    45. ASglucose
    46. AT-galactosidase (lactase)
    47. AUrestricting
    48. AVmembranes
    49. AWmitochondria,
    50. AXefficient
    51. AYproteases
    52. AZhigh

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Quiz am Ohne Titel, erstellt von Suzana Matana am 12/10/2020.
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English
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grade 12
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