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Question 5 from practice test 1:
The lac operon:
A. is found in eukaryotic cells
B. codes for the sequence of amino acids in lactase
C. regulates translation of mRNA
D. regulates transcription by turning on or off the production of a repressor protein
E. regulates DNA replication by turning on or off the production of an inducer protein
A, C and E are obviously false. The answer is D but I don't understand how it's not B. If I understand correctly, the repressor is constantly being made by the repressor gene and the only thing that dictates whether or not the gene for lactase (i guess that's short for beta-galactosidase) is being transcribed is the presence of the inducer (lactose) -
Here is Cliff's solution:
The lac operon in bacteria regulates gene expression by turning on or off the production of a repressor protein. The repressor protein, in turn, occupies the operator region of the operon, blocking transcription of the structural gene for lactase. When the sugar lactose is available, it inactivates the repressor protein, thereby allowing transcription of the structural gene for lactase. Lactase is then produced, and lactose digestion proceeds.
Am I missing something??
The lac operon:
A. is found in eukaryotic cells
B. codes for the sequence of amino acids in lactase
C. regulates translation of mRNA
D. regulates transcription by turning on or off the production of a repressor protein
E. regulates DNA replication by turning on or off the production of an inducer protein
A, C and E are obviously false. The answer is D but I don't understand how it's not B. If I understand correctly, the repressor is constantly being made by the repressor gene and the only thing that dictates whether or not the gene for lactase (i guess that's short for beta-galactosidase) is being transcribed is the presence of the inducer (lactose) -
Here is Cliff's solution:
The lac operon in bacteria regulates gene expression by turning on or off the production of a repressor protein. The repressor protein, in turn, occupies the operator region of the operon, blocking transcription of the structural gene for lactase. When the sugar lactose is available, it inactivates the repressor protein, thereby allowing transcription of the structural gene for lactase. Lactase is then produced, and lactose digestion proceeds.
Am I missing something??