CIE Nov 2015 v2 Paper 4 Q9

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(a) Some metals are essential to biochemical processes. 16 Complete the following table naming one metal in each case. biochemical process metal haemoglobin in oxygen transport transmission of nerve impulses enzyme cofactor PMT [2] (b) Enzymes are a special type of protein molecule that catalyse biochemical reactions. Explain briefly the mechanism by which an enzyme breaks down a substrate molecule.[3] (c) Disulfide bonds play an important role in the stability of some proteins such as the keratin in human hair. The amino acid involved in the formation of a disulfide bond is cysteine, H2NCH(CH2SH)CO2H. (i) At which level of protein structure (primary, secondary, tertiary) are disulfide bonds formed?[1] (ii) Use a functional group in cysteine to show how disulfide bonds are formed. (iii) What type of chemical reaction is this?[1] [1]UCLES 2015 9701/42/O/N/15<br /> 17 (d) The NMR spectrum of cysteine, H2NCH(CH2SH)CO2H, shows five absorptions. After shaking a solution of cysteine with a few drops of D2O, the NMR spectrum shows only two absorptions, E and F, shown below. PMT (i) Identify the two types of protons responsible for the absorptions E and F. EF[1] (ii) State and explain the splitting patterns of the absorptions E and F. EF[2] [Total: 11]UCLES 2015 9701/42/O/N/15 [Turn over<br />

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