Discussion
The tryptophan operon in Escherichia coli demonstrates level of regulation called .................. by the termination of transcription if tryptophan is abundant in cells.
Answer: C
The level of regulation is attenuation.
The trp leader region encodes a short peptide containing two tryptophan codons. When tryptophan is plentiful, the ribosome translates the leader quickly, which lets the transcript fold into a terminator hairpin, and RNA polymerase stops before the structural genes. When tryptophan is scarce, the ribosome stalls and an alternative antiterminator hairpin forms instead.
Corepression is the other control of the trp operon: the repressor, with tryptophan bound, blocks transcription from starting. It acts at initiation, not by terminating transcription. 'Activation' and 'termination' are not the names of this regulatory level.
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