Question 9 11 marks/11 minutes] This question is about regulation of expression
ID: 279446 • Letter: Q
Question
Question 9 11 marks/11 minutes] This question is about regulation of expression of the trp operon by control of attenuation. Assume there are intermediate levels of tryptophan, such that TrpR (the repressor protein) is inactive. a) Design a mutation within the 5' UTR of the trp operon that would give the outcome below. Explain how your mutation would result in that outcome 4 marks] 4 marks) b) Predict and explain the effect of insertion of T-A basepairs immediately after region 3, such that increased expression of the operon relative to wildtype decreased expression of the operon relative to wildtype i. ii. uracils are transcribed. Assume this insertion does not change the ability of regions 1, 2, 3 or4 to form stem-loop structures 13 marksExplanation / Answer
a.i. Nonsense mutation
Mutation in the operon that will change the functional codon to stop codon like Amber. The nonsense mutation, at intermediate trp concentration will cause the ribosomes to be free and the condition will formed like that in the case of trp starvation, and at this situation in absence of tryptophan there will be maximum expression of the operon. And in the absence of trp the repressor will remain unbound to the operon and allow full expression.
ii. Insertion/deletion
A mutation in the initiation codon will render the start of the gene expression even in the presence of tryptophan. Hence the expression will decrease.
b. The insertion of the T-A basepairs immediately after the 2 region of the trp operon will ncreases read-through at the trp attenuator. This suggests the enhanced Interaction between terminal uridines in mRNA and the template DNA strand that results into enhanced termination and suggest that there are no significant additional contributions from the DNA.
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