questionbase.50megs.com AS-Level Revision NotesAS Biology – Revision NotesUnit 1 – Core PrinciplesBiochemistry1. Carbohydrates have the general formula (CH2O)x. 2. The simplest carbohydrates are monosaccharides, e.g. glucose (C6H12O6), 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 β1-4 linkages, and is used in cell walls. Glycogen and starch are both coiled, with α1-4 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 denatured the hydrogen bonds are broken and so the active site changes shape. 15. Lipids are made of glycerol (propan-1,2,3-triol) and fatty acids. The fatty acids join via their carboxylic acid group to the hydroxyl groups on glycerol, forming three ester bonds and a triglyceride. 16. Saturated fatty acids are all single bonds, and are mainly fats and waxes, where as unsaturated fatty acids contain double bonds and form oils. Polyunsaturated fatty acids contain many double bonds. 17. If a phosphate group replaces one fatty acid then a phospholipid is formed. The phosphate is hydrophilic, but the fatty acids are hydrophobic, so they will form either a monolayered vesicle or a phospholipid bilayer (as in plasma membranes). 18. Benedict’s solution (containing copper sulphate) will test for a reducing sugar – it will turn orange/red in its presence upon heating. 20. Iodine will produce a blue/black colour in the presence of starch. 21. Biuret solution (copper sulphate and sodium hydroxide) will test for proteins, by turning lilac in its presence. 22. The emulsion test is for lipids – dissolve the lipid in ethanol, then pour into water. A fine emulsion is formed if it is a lipid. 23. Chromatography is used to separate out soluble components of a mixture (e.g. amino acids). This is done by calculating the Rf value for a specific solvent – solventby movedDistancespotby movedDistanceRf=. 24. Two-way chromatography can be more accurate, as two different solvents are used, and so the mixture can be more easily separated. 25. Water is essential to life due to the following properties:
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