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AS-Level Revision Notes

AS Biology – Revision Notes
Unit 1 – Core Principles
Biochemistry
1. Carbohydrates have the general formula (CH2O)x.
2. The simplest carbohydrates are monosaccharides, e.g. glucose (C 6H12O6), and are monomers.
3. Monosaccharides can join together to form disaccharides in a condensation reaction, forming a glycosidic bond. This can be broken by hydrolysis:
4. Polysaccharides are formed from multiple glycosidic bonds, and include starch, glycogen and cellulose. 5. 1-4 glycosidic bonds create straight chains, whereas side chains are produced from 1-6 bonds.
6. Cellulose is fibrous, with β 1-4 linkages, and is used in cell walls. Glycogen and starch are both coiled, with α 1-4 linkages, and 1-6 side chains, and are used for storage.
7. Amino acids are the monomers of proteins – they have an amino group at one end, and a carboxylic acid group at the other.
8. The ‘R’ group distinguishes one amino acid from another – there are about 20 in total; those that are needed in the diet are called essential amino acids.
9. Some amino acids can be synthesised by transamination.
10. Amino acids bond like monosaccharides, creating peptide bonds.
11. Fibrous proteins, e.g. collagen and keratin, have long, straight, polypeptide chains.
12. Globular proteins, e.g. gels and enzymes, have a roughly rounded shape.
13. Proteins have four different structures:
a. The primary structure is the basic sequence of amino acids.
b. The secondary structure is how the chain becomes coiled and folded due to the bonding.
c. The tertiary structure is the 3D structure of the protein, due to disulphide bridges and hydrogen bonding.
d. The quaternary structure is when more than one protein is joined together (e.g. in haemoglobin). 14. The tertiary structure of an enzyme gives rise to the active site – when an enzyme is