Question: What effect will these four mutant leader peptide genes have on the re

Question

Question: What effect will these four mutant leader peptide genes have on the regulation of the
tryptophan operon? Justify your answer.

2) The following mutations (mutant bases are shown in small letters) occur in the leader polypeptide gene region of the tryptophan operon. Also shown is the wild type sequence of the coding strand of the leader peptide gene. Note: (i) Assume that there is only one methionine codon (ATG) between the 5' end of the tryptophan operon encoded mRNA and the start codon for the trpE gene. Note:ii) The codon GGG codes for glycine (Gly) fMet Lys Ala Ile Phe Val Leu Lys Gly Trp Trp Arg Thr Ser Stop wild type- ATG AAA GCA ATT TTC GTA CTG AAA GGT TGG TGG CGC ACT TCC TGA mutant #1-ATG AAA GCA ATT TTC GTA CTG AAA GGT TGa TGa CGC ACT TCC TGA mutant #2-ATG AAA GCA ATT TTC GTA CTG AAA GGT gGG gGG CGC ACT TCC TGA mutant #3-CTG AAA GCA ATT TTC GTA CTG AAA GGT TGG TGG CGC ACT TCC TGA mutant #4-ATG AAA GCA ATT TTC GTA CTG AAA GGT TGG gGG CGC ACT TCC TGA

Explanation / Answer

All of the mutant have only one Mitheonine encoding at the starting region. So when small amount of mitheonine is present in the cytoplasm of cell then it can also initiate the process of translation.

1. In the first mutant cell the triplet codons of TGG TGG is mutated by TGa TGa which is a stop codon leads to termination of m R NA formation.

by the by the mutation in mutant first the triplet is changed by the stop codon so the process of RNA formation will terminate here.

In the mutant second the codon of tryptophan is replaced by the code on which codes for glycine. The codon changes occurs at the m RNA but the ultimate result of this change occurs on the protein. Here the trp codon is changed by GGG which codes for glycine. so a mutated protein well formed.

the the replacement of tryptophan with gly leads to disturbance of the structure of protein. Which is due to the affect on bonding pattern between amino acids.

Mutant 3: In the mutant third the codon ATG which codes AUG in mRNA is mutated by cTG.

This mitation leads to the inhibition of protein synthesis. for protein synthesis the start codon is AUG required at the start site of mRNA. Here mutation in DNA changed the site which is called as start site. so due to the absence of start site synthesis of protein is not initiated.

4. in the mutant 4 point mutation is occured which changed the triplet codons.

The normal codon codes for trp and the mutated codon codes for glycine so this change affects the globular structure if protein. The results of this mutation is mutated structured protein.

Same mutation is appeared in mutation second but there mutation is appeared at twice so in mutant second hi effects in the disturbance of protein folding appears as compared to Mutant 4.

mutant 4 have single point mutation but the mutant 2 have same mutation twice so high affect in mutant 2.

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