Proteinsynthesis - HKALE 1989 Biology Paper II.3 HKALE 1999...

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HKALE 1989 Biology Paper II......................................................................................3HKALE 1999 Biology Paper II......................................................................................3
QuestionsHKALE 1989 Paper IIHKALE 1989 Paper II8.(a)The following are codons for some of the amino acids and the start signal for translation found in messenger RNA:CondonAmino acidDiagrammatic representation of the corresponding amino acidCUULeucineLeuAACAsparagineAsnAUG*MethionineMetGCAAlanineAlaUGCCysteineCysCAUHistidineHis* The codon AUG serves as a start signal and initiates synthesis of a polypeptide.Answer the following questions with reference to the synthesis of the peptide shown below:HisLeuMetCysCOOHNH2(i)Using ONE labelled diagram ONLY, explain the roles of the various components involved in protein synthesis. In your diagram, you should indicate:(1)the base sequence of the messenger RNA,(2)the site of protein synthesis,(3)the direction of translation,(4)the base sequences of the anticodons of the transfer RNAs, and(5)the stage at which the amino acids, methionine and histidine, are linked together while leucine is forming a bond to the growing peptide and cysteine is still in the pool of free amino acids.(10 marks)(ii)What is the base sequence of the corresponding segment on the DNA molecule ?(2 marks)
(b)Explain the significance of polysomes in protein synthesis.(2 marks)(c)Explain the meaning of the following terms with reference to codons:(i)universal(ii)degenerate(iii)nonsense triplets(6 marks)Suggested Solution…HKALE 1989 Biology Paper IIHKALE 1989 Biology Paper II

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