Ans: A. The tryptophan synthesizing genes are transcribed if tryptophan is Scarce. When tryptophan is abundant, tryptophan binds to the repressor and the repressor then binds to the operator, causing transcription of tryptophan synthesizing genes stop. In the E. coli, five genes (trp E, trp D, trp C, trp B, trp A) encode enzymes that synthesize the tryptophan amino acid. The gene products are anthranilate synthetase (product of trp E), phosphoribosyl anthranilate transferase (trp D), phosphoribosyl anthranilate isomerase-indole glycerol phosphate synthetase (trp C), tryptophan synthetase b (trp B), and tryptophan synthetase a (trp A). These genes are expressed only when tryptophan is scarce (limiting). The trp repressor bind to DNA and blocks transcription only when tryptophan is present. When tryptophan is around, it attaches to the repressor molecules and changes their shape so they become active. A small molecule like tryptophan, which switches a repressor into its active state, is called a corepressor. Solution Ans: A. The tryptophan synthesizing genes are transcribed if tryptophan is Scarce. When tryptophan is abundant, tryptophan binds to the repressor and the repressor then binds to the operator, causing transcription of tryptophan synthesizing genes stop. In the E. coli, five genes (trp E, trp D, trp C, trp B, trp A) encode enzymes that synthesize the tryptophan amino acid. The gene products are anthranilate synthetase (product of trp E), phosphoribosyl anthranilate transferase (trp D), phosphoribosyl anthranilate isomerase-indole glycerol phosphate synthetase (trp C), tryptophan synthetase b (trp B), and tryptophan synthetase a (trp A). These genes are expressed only when tryptophan is scarce (limiting). The trp repressor bind to DNA and blocks transcription only when tryptophan is present. When tryptophan is around, it attaches to the repressor molecules and changes their shape so they become active. A small molecule like tryptophan, which switches a repressor into its active state, is called a corepressor..

1. Ans: A.
The tryptophan synthesizing genes are transcribed if tryptophan is Scarce. When tryptophan is
abundant, tryptophan binds to the repressor and the repressor then binds to the operator, causing
transcription of tryptophan synthesizing genes stop.
In the E. coli, five genes (trp E, trp D, trp C, trp B, trp A) encode enzymes that synthesize the
tryptophan amino acid. The gene products are anthranilate synthetase (product of trp E),
phosphoribosyl anthranilate transferase (trp D), phosphoribosyl anthranilate isomerase-indole
glycerol phosphate synthetase (trp C), tryptophan synthetase b (trp B), and tryptophan synthetase
a (trp A). These genes are expressed only when tryptophan is scarce (limiting).
The trp repressor bind to DNA and blocks transcription only when tryptophan is present. When
tryptophan is around, it attaches to the repressor molecules and changes their shape so they
become active. A small molecule like tryptophan, which switches a repressor into its active state,
is called a corepressor.
Solution
Ans: A.
The tryptophan synthesizing genes are transcribed if tryptophan is Scarce. When tryptophan is
abundant, tryptophan binds to the repressor and the repressor then binds to the operator, causing
transcription of tryptophan synthesizing genes stop.
In the E. coli, five genes (trp E, trp D, trp C, trp B, trp A) encode enzymes that synthesize the
tryptophan amino acid. The gene products are anthranilate synthetase (product of trp E),
phosphoribosyl anthranilate transferase (trp D), phosphoribosyl anthranilate isomerase-indole
glycerol phosphate synthetase (trp C), tryptophan synthetase b (trp B), and tryptophan synthetase
a (trp A). These genes are expressed only when tryptophan is scarce (limiting).
The trp repressor bind to DNA and blocks transcription only when tryptophan is present. When
tryptophan is around, it attaches to the repressor molecules and changes their shape so they
become active. A small molecule like tryptophan, which switches a repressor into its active state,
is called a corepressor.