State whether or not tryptophan levels would be high in cell for the situations
ID: 260917 • Letter: S
Question
State whether or not tryptophan levels would be high in cell for the situations below:1. A nonsense mutation in the structural gene codes
2. A mutation in the operator that prevents binding by regulatory protein
3. A mutation in UTR region 3 so it cannot bind to region 2 State whether or not tryptophan levels would be high in cell for the situations below:
1. A nonsense mutation in the structural gene codes
2. A mutation in the operator that prevents binding by regulatory protein
3. A mutation in UTR region 3 so it cannot bind to region 2
1. A nonsense mutation in the structural gene codes
2. A mutation in the operator that prevents binding by regulatory protein
3. A mutation in UTR region 3 so it cannot bind to region 2
Explanation / Answer
Answer-1
Nonsense mutation i.e. stop codon in the structural gene will lead to premature termination and tryptophan synthesis will not take place.
Answer-2
Operator mutation which will inhibit the binding of regulatory protein results in higher levels of tryptophan in the cell. because regulatory protein + tryptophan binds to operator region inhibit operon transcription i.e. tryptophan synthesis but if this regulatory protein is unable to binds than in the excess of tryptophan cell will not sense the presence of tryptophan this will lead to the excess synthesis of trp.
Answer-3
The 5' UTR (leader) of the trp operon contains 4 regions (1 complementary to 2, 2 to 3, 3 to 4)
This allows different secondary structures to form, but only 1 causes attenuation
When cellular levels of tryptophan are high, regions 1+2, 3+4 pair. The 3+4 hairpin plus a string of uracil nucleotides forms the attenuator, causing transcription to be terminated before the trp structural genes can be transcribed
When cellular levels of tryptophan are low, regions 2 and 3 pair; this structure does not function as a terminator. The 2+3 hairpin structure is termed an anti- terminator. So it will not increase the level of tryptophan in the cell.
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