Which of the following events occur when E. coli is straved for tryptophan ?a)The ribosome translates the leader peptide completelyb)Transcription reads through attenuator into trp EDCBAc)Tryptophanyl tRNA is not formedd)A stem loop structure involving regions 3 and 4 is formed at attenuator site.Correct answer is option 'B,C'. Can you explain this answer?

Question

Answer

When E. coli is starved for tryptophan, several events occur as a response to the depletion of this essential amino acid. The correct options are B and C, which are explained in detail below:

b) Transcription reads through attenuator into trp EDCBA:
In the absence of tryptophan, the ribosome translating the leader peptide completes the translation. This leads to the formation of the amino acid sequence called the leader peptide. The leader peptide contains a region called the attenuator. The attenuator is a regulatory sequence located upstream of the trp operon, which is responsible for the production of tryptophan.

The attenuator sequence has four regions, numbered 1 to 4. When tryptophan levels are low, the ribosome translating the leader peptide stalls at the tryptophan codons in region 1. This stalling prevents the formation of a stem loop structure involving regions 2 and 3 of the attenuator. As a result, the RNA polymerase continues transcription and reads through the attenuator into the trp operon, allowing the synthesis of enzymes involved in tryptophan biosynthesis.

c) Tryptophanyl tRNA is not formed:
In the absence of tryptophan, the trp operon is derepressed, and the synthesis of tryptophan enzymes is initiated. However, tryptophan biosynthesis cannot proceed without the presence of tryptophanyl tRNA. Tryptophanyl tRNA is responsible for carrying the amino acid tryptophan to the ribosome during protein synthesis. When tryptophan levels are low, the tryptophanyl tRNA is not formed, leading to a decrease in protein synthesis.

Therefore, when E. coli is starved for tryptophan, the transcription reads through the attenuator into the trp operon, allowing the synthesis of tryptophan enzymes. However, the absence of tryptophanyl tRNA prevents the biosynthesis of tryptophan and reduces protein synthesis.

Top Courses for IIT JAM

Suggested Free Tests

Related Content

Schools

Competitive Examinations

Quick Access Links

Technical Exams