Gk3 in Mamals

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SECTION A – PROTEINS (APPROX 1h) Answer all THREE questions QUESTION ONE (20 MARKS) a) The figure below shows the structure of the amino acid histidine. The pK values for ionisable groups of histidine are: pK1 (COOH) = 1.82, pK2 (NH3+) = 9.17, pKR = 6.00. Use these values to redraw histidine showing ionisable groups in their predominant forms at pH 4 and pH 12; label each structure with the relevant pH. [5 marks] a) Now draw histidine and a different amino acid linked via a peptide bond. Label the peptide bond, the N-terminus and the C-terminus of your peptide. [5 Marks] b) Name ONE example of each type of amino acid listed below: [1 mark each] Example bond/non-bonding interaction sulfur Cysteine disulfide bridge hydrophobic Valine hydrophobic effect hydroxy Serine hydrogen bond acidic Glutamate ionic interaction amide Glutamine hydrogen bond c) For each of the amino acids listed above name ONE type of bond or non-bonding interaction in which the RGROUP participates, contributing to the stability of the native three-dimensional structure of proteins. (for answer see above) [5 Marks] QUESTION TWO (20 MARKS) domain The figure below shows a cartoon of a class I major histocompatibility complex protein. Examine the diagram, then answer the following questions: a) What type of protein is this (globular, fibrous, membrane)? Justify your answer using information in the diagram. [2 marks] This is a membrane protein as it is shown to have a trans-membrane section (helix) b) On the diagram, label two types of secondary structure found in the protein. [2 marks] α-helix β sheet c) What type of bond is responsible for stabilization of secondary protein structure? [1 marks] Secondary structures are stabilized by peptide hydrogen bonds d) On the diagram,

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