CIE Jun 2014 v2 Paper 4 Q6

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14 Section B Answer all the questions in the spaces provided. PMT This question looks at the formation and breakdown of protein chains in the body. (a) Proteins are formed from chains of amino acid monomers joined together. The structures of two amino acids, valine and serine are shown. CH3 CH3 OH HO OH NH2 valine (val) NH2 serine (ser) (i) Draw the structure of the dipeptide val-ser, showing the peptide bond in displayed form. (ii) What type of reaction has taken place in order to form this dipeptide?(iii) Identify the other molecule produced in this reaction.[4] (b) Both DNA and RNA are involved in protein synthesis. Complete the table to show three differences between the structures of DNA and RNA. DNA RNAUCLES 2014 9701/42/M/J/14 [3]<br />
 15 (c) In protein synthesis, sections of the DNA are copied by mRNA and this, in turn, is read by the ribosome in order to assemble the amino acids for the new protein chain. Each group of three bases codes for one amino acid, with some amino acids having several codes. The codes are summarised in the table. PMT UUU UUC UUA UUG CUU CUC CUA CUG AUU AUC AUA AUG GUU GUC GUA GUG phe phe leu leu leu leu leu leu ile ile ile met/ start val val val val UCU UCC UCA UCG CCU CCC CCA CCG ACU ACC ACA ACG GCU GCC GCA GCG ser ser ser ser pro pro pro pro thr thr thr thr ala ala ala ala UAU UAC UAA UAG CAU CAC CAA CAG AAU AAC AAA AAG GAU GAC GAA GAG tyr tyr stop stop his his gln gln asn asn lys lys asp asp glu glu UGU UGC UGA UGG CGU CGC CGA CGG AGU AGC AGA AGG GGU GGC GGA GGG cys cys stop trp arg arg arg arg ser ser arg arg gly gly gly gly In general the amino acid chains start with the code AUG, and end with one of the three stop codes shown in the table. (i) Use the abbreviations to show the sequence of amino acids in the peptide for the base sequence shown.AUGCUAACACCGGAGUAA(ii) Sometimes an error can occur in the base sequence. What are these errors called?(iii) This type of error can lead to the formation of a protein with a different structure from the original, as in sickle cell anaemia. In this case the amino acid glutamic acid (glu) is replaced by valine (val) in the protein as a result of one base being changed in a three base code. Use the table to suggest the change of base that causes this.[3]UCLES 2014 9701/42/M/J/14 [Total: 10] [Turn over<br />

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