2.1 Molecules to metabolism: page 43 (see page 43 for learning objectives)
Elements in living things (page 43):

Carbon, hydrogen, oxygen and nitrogen are the four most common elements found in living organisms
Carbon, hydrogen and oxygen are found in all the key organic molecules (proteins, carbohydrates, nucleic acids and lipids)

Proteins and nucleic acids also contain nitrogen

Any compound that does not contain carbon is inorganic.
Molecular biology explains the roles of the chemical substances involved in life processes
Carbon compounds including carbohydrates, lipids, proteins and nucleic acids form the basis for life.

Carbon atoms (pages 43-44):

(see page 43, figure 2.1)

Every organic compound contains two or more atoms of carbon
Carbon atoms can also form double and triple bonds with other atoms, so increasing the variety in the molecular structure of organic compounds.
Carbohydrates, proteins, lipids and nucleic acids are the main types of carbon

Carbon compounds - the building blocks of life (pages 44-46) :

Carbohydrates are compounds that contain only the elements carbon, hydrogen and oxygen (and are the most abundant group of biological molecules)
Lipids contain the same three elements, but with much less oxygen
Lipids may contain small amounts of other elements such as phosphorus.
Proteins, unlike carbs and lipids, always contain nitrogen (sulfur, phosphorus and other elements are also often present)

Many organic molecules are very large and complex, but they are build of small subunits.

Small subunits called monomers are build into complex molecules called polymers in a process known as polymerisation.

Carbohydrates (page 45):

The most abundant category of molecule in living things.
In both plants and animals, they are used as a source of energy.

Carbohydrates occur in different forms:

Monosaccharides (with the general formula (CH2O)n where n= the number of carbon atoms in the molecule, are monomers- single sugars made up of one subunit)

Disaccharides are sugars with two subunits joined together by a condensation reaction (see page 46)
Polysaccharides are long molecules consisting of a chains of monosaccharides linked together

(See table 2.4, page 54)

Monosaccharide examples: glucose, galactose, fructose

Example of use in plants:
Fructose makes fruits taste sweet, and attracts animals to eat them- thereby dispersing the seeds inside
Example of use in animals:
Glucose is the source of energy for cell respiration - it is obtained from the digestion of carbohydrate foods.

Disaccharide examples: lactose, maltose, sucrose

Example of use in plants:
Sucrose is transported from leaves to storage tissues and other parts of the plant to provide an energy
Example of use in animals:
Lactose is found in milk and provides energy for young mammals

Polysaccharide examples: starch, glycogen, cellulose

Example of use in plants:
Cellulose is a structural component of plant cell walls + starch is used as a food store
Example of use in animals:
Glycogen is the storage carbohydrate of animals, found in the liver and muscles.

Lipids (page 45):

Insoluble in water, but do dissolve in organic solvents
Known as energy storage molecules in plants and animals

One group: triglyceride lipids, includes fats and oils
Solid=fat, liquid=oil.

Animals store energy as fat whereas plants store oils
Lipids contain twice as much energy per gram as carbohydrates

Second group of lipids: steroids, which consist of four interlinked rings of carbon (examples of steroids: vitamin D and cholesterol)

Protein (page 45): READ UP!!!!

Proteins are built up of building blocks called amino acids
The simplest amino acid is glycine
There are more than 100 naturally occurring amino acids, but only 20 are used in building the bodies of living things.
Proteins are built up of amino acids in condensation reactions.

Nucleic acids (page 46):

Found in all living cells and in viruses
Two types of nucleic acid found in cells are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
DNA is found in the nucleus, mitochondria and chloroplasts of eukaryotes, while RNA maybe occur in the nucleus but is found usually in the cytoplasm.
Vital to inheritance and development
Nucleic acids are long molecules consisting of chains of units called nucleotides
Each nucleotide consists of a pentose sugar - ribose in RNA and deoxyribose in DNA - linked to phosphoric acid and an organic base.
Nucleic acid chains are longer and more complex than those found in proteins.

Condensation (p46-47):

In a condensation reaction, two molecules can be joined to form a larger molecule, held together by strong covalent bonds
Condensation is an example of an anabolic reaction (which builds up monomers to form macromolecules)
An enzyme is required to catalyse the process of condensation, and it produces one molecule of water

For example:
Glucose(monosaccharide) + Galactose(monosaccharide) -▸ Lactose(disaccharide) + water

Two amino acids can be linked to form a dipeptide
When more than two amino acids are joined in this way, a polypeptide is formed (polypeptide chains form protein molecules)

Hydrolysis (p48):

Hydrolysis reactions occur every time food is digested. These reactions involve breaking down polysaccharides, polypeptides and triglycerides into smaller subunits.
Hydrolysis is a reaction of a catabolic reaction, in which macromolecules are broken down into monomers.
Water molecules are used in hydrolysis reactions, which are the reverse of anabolic reactions.
Enzymes are used to catalyse the reactions.

Hydrolysis of a starch (a polysaccharide) : uses water and produces many molecules of glucose
Hydrolysis of a protein (made of polypeptide chains) : uses water and produces many amino acids
Hydrolysis of a triglyceride: uses water and produces fatty acids and glycerol molecules

	Created by amandalouisejm over 9 years ago

Note on Molecular Biology test revision notes, created by amandalouisejm on 03/11/2014.

Molecular Biology test revision notes