Question

The trp operon is turned off when its repressor protein binds with corepressor which is a molecule of

• A. Metabolite
• B. Specific amino acid
• C. Tryptophan
• D. All of the above

Answer 1

Answer: (D)

All of the above

In presence of tryptophan in the cell, two tryptophan molecules serve as corepressor and bind to the trp repressor. This binding activate the inactive repressor to bind to the trp operator. Binding of the tryptophan-repressor complex at the operator prevents the RNA polymerase from binding the downstream genes and thus presents their transcription. Here, tryptophan serve as a corepressor and inhibits the expression of genes not by direct binding to DNA but instead indirectly regulates gene expression by binding to repressors. Tryptophan is among 22 standard amino acids and is one of essential amino acids in the human diet which is encoded by codon UGG. Any substance that is produced during metabolism (both catabolism and anabolism) are known as metabolites. Tryptophan is produced during protein digestion and tryptophan biosynthetic pathway; hence is a metabolite. Option D is the correct answer.