CIE Nov 2013 v2 Paper 4 Q6

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Examiners For Use 12 Section B Answer all the questions in the spaces provided. (a) Protein molecules are formed by the polymerisation of amino acids in the body. The structures of three amino acids are given. H2N OH HO OH glycine (gly) NH2 serine (ser) OH NH2 valine (val) (i) How many different tripeptides can be made using one molecule of each of the amino acids shown?(ii) Draw the tripeptide ser-gly-val, showing the peptide bonds in displayed form. (iii) Within the tripeptide, which amino acid provides a hydrophobic side chain?(iv) Polypeptide chains can form bonds giving proteins their secondary and tertiary structures. Using the tripeptide in (ii), state two types of bonding that can be formed and the groups in the tripeptide that are involved in this bonding. bondgroupsbondgroups[6]UCLES 2013 9701/42/O/N/13<br /> Examiners For Use 13 (b) Enzymes are particular types of proteins that catalyse chemical reactions. The ef ciency of enzymes can be reduced by the presence of other molecules known as inhibitors. Explain how both competitive and non-competitive inhibitors prevent enzymes from working ef ciently. (i) competitive inhibitors(ii) non-competitive inhibitors(iii) The graph shows the rate of an enzyme-catalysed reaction against the substrate concentration in the absence of an inhibitor. rate of reaction concentration of substrate On the same axes, sketch a graph showing the rate of this reaction if a non-competitive inhibitor was present. [4] [Total: 10]UCLES 2013 9701/42/O/N/13 [Turn over<br />

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