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Flashcards

Carbohydrates

Julia Spychalska CH112: Bio-organic chemistry English 77 cards

Cards in this deck (77)

  1. 1What are the two simple carbohydrates?glucose and fructose
  2. 2What are stereoisomers?compounds that have the same molecular formula and sequence of bonds but differ in the relative disposition of their atoms in space.
  3. 3what are enantiomers?non-superimposable mirror images. They have identical physical and chemical properties except in their ability to rotate plane-polarized light. They rotate light in equal and opposite directions.
    SYMMETRICAL before flipped
  4. 4What are diastereomers?Stereoisomers that are not enantiomers, ie. they are not mirror image related.
    Diastereomers have different physical properties and similar chemical properties. They result from the presence of two or more stereoisomers in a molecule.
    NOT SYMMETRICAL (even before flipping)6
  5. 5What are epimers?A pair of diastereomers that differ only in the configuration at a single atom.
  6. 6When is a molecule chiral?If it cannot be superimposed on its mirror image. Chiral molecules have no elements of symmetry and they usually contain a stereogenic centre (stereocentre)
  7. 7What makes a stereocentre?A carbon atom bonded to four different substituents.
  8. 8How many stereoisomers do aldotrioses have?2 stereoisomers, one stereogenic centre.
  9. 9How many stereoisomers do aldotetroses have?4 stereoisomers, two stereocentres.
  10. 10How many stereoisomers do aldopentoses have?8 stereoisomers, 3 stereocentres.
  11. 11How many stereoisomers do aldohexoses have?16 stereoisomers, 4 stereocentres.
  12. 12What is mutarotation?The change in optical rotation towards and equilibrium value. It occurs by a reversible ring opening of each anomer to the open chain form, followed by reclosure.
  13. 13What is the anomeric effect?the preference for the axial alpha-anomer.
    It is a stabilising electronic effect that occurs when a lone pair of electrons on oxygen is oriented trans coplanar to a polar C-X bond.
  14. 14What are monosacchride acetals called?glycosides
  15. 15What are glucose acetals called?glucosides
  16. 16What are mannose acetal called?mannosides
  17. 17What are fructose acetals called?fructosides
  18. 18What makes some sugars good reducing agents?if they have a free hydroxyl group at the anomeric centre (i.e. hemiacetal)
  19. 19What enzyme is starch hydrolysed by and what is produced?enzyme diastase, forming disaccharide maltose (reducing sugar)
  20. 20What is formed during partial hydrolysis of cellulose?an isomeric disaccharide called cellobiose (reducing sugar)
  21. 21What are the two fractions of starch?amylopectin (80%) - soluble in cold water
    amylose (20%) - insoluble in cold water
  22. 22Polysaccharide Secondary Structure: Why is the nature of the glycosidic link important?because certain angle combinations result in more stable, less hindered conformations.
  23. 23What blood type is a universal donor?Type O
  24. 24What blood type is a universal acceptor?Type AB
  25. 25What are the frontline helpers for leukocytes on their surface?carbohydrates called sialyl Lewis x acids
  26. 26What are simple carbohydrates?monomers that cannot be hydrolysed to smaller carbohydrates.
  27. 27What are complex carbohydrates?They are composed of two or more monosaccharides, covalently linked.
  28. 28How are cyclic hemiacetals made?If the hydroxyl and carbonyl group are in the same molecule, an intramolecular nucleophilic reaction can occur.
  29. 29What are anomers?Cyclisation of hemiacetal creates a new stereocentre at C-1, producing two cyclic forms which are diastereomeric, called anomers.
  30. 30What is the beta anomer?The anomer with the anomeric hydroxyl group up i.e. cis to the CH2OH
  31. 31What is the alpha anomer?The anomer with the hydroxyl down and trans to the CH2OH group.
  32. 32Why is glucose not in an open chain form? (i.e. with aldehyde and hydroxyl groups)The formation of cyclic hemiacetals causes lack of the free aldehyde group
  33. 33What is a pyranose?A six membered ring of glucose
  34. 34Where is the oxygen and carbon placed in Haworth projections?the ether oxygen is placed at the upper right while the anomeric carbon is placed at the right vertex
  35. 35How do you convert Fischer projections to Haworth projections?1. OH groups on the RIGHT are DOWN in Haworth projections
    2. OH groups on the LEFT are UP
    3. For D-monosaccharides, the terminal CH2OH is UP
  36. 36Which carbohydrate does aldopentose prefer?pyranose
  37. 37Which carbohydrate does aldohexose prefer?pyranose
  38. 38Which carbohydrate does ketohexose prefer?mixture o pyranose and furanose
  39. 39What accelerates mutarotation?acids and bases
  40. 40Why do pyranose rings have similar strain energies as in cyclohexanes?The C-O-C bond angle (111) is close to the C-C-C bond angle (109.5)
  41. 41What happens to the equatorial and axial substituents during chair ring flipping?All axial substituents become equatorial and all equatorial ones become axial.
  42. 42How do you convert Haworth projections to a chair?1. Draw the Haworth projection with the ring oxygen at the top right.
    2. Raise the left vertex carbon (C4) above the ring plane.
    3. Lower the anomeric carbon (C1) below the ring plane.
  43. 43Which of the axial or equatorial conformations are most stable?An all equatorial conformation is the most stable.
  44. 44Which rings adopt an envelope conformation?furanose and pyranose
  45. 45Why is the anomeric centre most reactive/ most susceptible to nucleophilic attack?It has two C-O bonds, which makes it more susceptible to nucleophilic attack due to the electron withdrawing effect of the two oxygen's.
  46. 46How are acetals at the anomeric centre of monosaccharides produced?Cyclic forms of monosaccharides are hemiacetals and can react with alcohol under acidic catalysis to give acetals at the anomeric centre.
  47. 47Why do glycosides not show mutarotation?They are not in equilibrium with the open chain form
  48. 48What is aglycone?An alcohol produced by the acidic hydrolysis of glycosides
  49. 49Which reagent gives a silver mirror with reducing hemiacetal sugars?Tollen's reagent
  50. 50Which reagent gives a red precipitate with a reducing hemiacetal sugar?Benedict's and Fehling's
  51. 51Disaccharides contain what type of bond?They contain a glycosidic bond between C-1 of one sugar and a hydroxyl group of the other sugar.
  52. 52What are maltose and cellobiose and what are they composed of?They are reducing sugars, composed of two glucose anomers
  53. 53What is the glycosidic bond in maltose and cellobiose?The glycosidic bond is between C1 of one glucose and C4 of the second sugar, this is a 1-4'-link.
  54. 54What is lactose and what is it composed of?It is a disaccharide (and reducing sugar) and it contains two different monosaccharide units: D-glucose and D-galactose.
  55. 55Sucrose: what is it consist of and what is the link?Not a reducing sugar. Hydrolysis of sucrose yields glucose and fructose. The two sugars are glycosides and sucrose has a 1,2'-glycosidic link.
  56. 56What are the three important glucans?starch, cellulose and glycogen
  57. 57What is a homopolysaccharide?Polysaccharide consisting of a single monosaccharide
  58. 58What is a hetero polysaccharide?Polysaccharide consisting of more than one monosaccharide
  59. 59What is the primary structure of polysaccharides?1. Monomers (homo/heteropolysaccharides)
    2. sequence of monomers
    3. The types of links (alpha or beta)
    4. the type of glycosidic linkage (1,4' or 1,6')
    5. Basic geometry- linear, branched, cyclic
  60. 60What is cellulose composed of? (and link)D-glucose units linked by 1,4'-B-glycoside bonds
  61. 61What does amylose consist of?100-1000 D-glucose monomers linked by 1,4'-a-glycosidic bonds
  62. 62How is starch hydrolysed?It is hydrolysed by enzymes called glycosidase to give glucose. They hydrolyse alpha-glycoside linkages, not beta ones.
  63. 63What links does amylopectin have?It has 1,4'-a-glycoside linkages, but it is branched with a 1,6'-a-glycoside link every 2-25 glucose units.
  64. 64How does glycogen compare to amylopectin?It also has 1,4'-a- and 1,6'-a-glycosidic link, but it is more highly branched.
  65. 65What enzyme catalyses glycogen breakdown? (giving what?)glycogen phosphorylase, to give glucose-1-phosphate
  66. 66How is a sufficient amount of glucose available quickly from glycogen?Because glycogen is highly branched, there are many non-reducing termini at which the phosphorylase can "nibble away"
  67. 67What are the steps of glycogen breakdown?1. Phosphorylase cannot cleave the 1,6'-glycosidic link, so it stops.
    2. Transferase shifts a block of 3 terminal glucose units from the branch (link) point.(leaving one glucose)
    3. a-1,6'-glycosidase (debranching enzyme) removes the 1,6'- linked glycose at the branch point.
    4. Phosphorylase continues degrading the chain until it reaches another branch, and so forth.
  68. 68What is the secondary structure of polysaccharides?The way in which the polysaccharide backbone is folded to give the 3D shape.
    The secondary structure is a consequence of local conformations that result from rotations about the single bonds of the glycosidic linkage.
  69. 69What is the tertiary structure of the polysaccharides?The way in which the entire polysaccharide backbone is arranged in 3D space.
  70. 70What is the quaternary structure of the polysaccharides?The way in which polysaccharide chains are aggregated with other polysaccharide chains.
  71. 71How are insoluble, rigid, and fibrous polymers made? (Ribbons/B-linked chains)The linear arrangement of B-linked glucose units in cellulose presents a uniform distribution of OH's on the outside of each chain. When two or more cellulose chains make contact, the hydroxyl groups are ideally located to form hydrogen bonds, giving these rigid structures.
  72. 72What are glycosaminoglycans?They consist of linear chains of repeating disaccharides in which one (or both) of the monosaccharide units consists of at least one negatively charged sulphate or carboxylate group.
  73. 73How is the carbohydrate group linked in the O-linked oligosaccharide? (and what is the carb)It is linked to polypeptide chains via the hydroxyl groups of serine, threonine, or hydroxylysine. The residue is usually N-acetyl galactosamine.
  74. 74How is the carbohydrate group linked in N-linked oligosaccharides?It is attached to the protein via the amide nitrogen of asparagine to N-acetyl glucosamine.
  75. 75What determines the blood type?The structure of the glycoproteins attached to the surface of the blood cells.
  76. 76What happens when injury occurs?The cells at the site of trauma display selectins(proteins) that signal the site of injury and bind sialyl Lewis x acids. Binding causes adhesion of leukocytes at the infected area, causing inflammation.
  77. 77How do anti-flu agents work?They inhibit the enzyme (neuramidase) that cleaves the glycosidic bond of sialic acid, which prevents the freeing of the virus.

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CH112: Bio-organic chemistry (Carbohydrates) Flashcards on Carbohydrates, created by Julia Spychalska on 31/03/2017.
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