The trp operon includes five genes needed for tryptophan synthesis in E. coli -

Question

The trp operon includes five genes needed for tryptophan synthesis in E. coli - trpE, trpD, trpC, trpB and trpA (listed in order on the operon).  If a nonsense mutation occurred at the beginning of trpC:

how long would be the transcript of the operon?

AND how many proteins would be translated?

A. the transcript would stop after trpA and only trpE and trpD proteins would be functional

B. The transcript wouls stop after trpC and only trpE, trpD, and part of trpC would be translated

C. The transcript would stop at TrpE and none of the protiens would be translated

D. The transcript would stop at TrpC and only trpE and trpD proteins would fold correctly

A. the transcript would stop after trpA and only trpE and trpD proteins would be functional

B. The transcript wouls stop after trpC and only trpE, trpD, and part of trpC would be translated

C. The transcript would stop at TrpE and none of the protiens would be translated

D. The transcript would stop at TrpC and only trpE and trpD proteins would fold correctly

Explanation / Answer

If the sense codon (which is functional to code amino acid) changes in to stop codon(non sense) by a mutation, those are considered to be as non sence mutations.

Here, in tryptophane operon, the five genes codes for five different enzymes. Eg: Try E codes for anthranilate synthase.

As the non sense mutation occrus in begining of trp C, the transcription of genes, E and D won't be effected. Hence their products will function normal.

Hence the answer is option D. The transcript would stop at TrpC and only trpE and trpD proteins would fold correctly

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