Molecular Genetics of Prokaryotes Problem Set

Problem 14: Effect of the absence of glucose

Tutorial to help answer the question

An E. coli cell is grown in the absence of glucose. Which of the following will be true?

A. The level of cyclic AMP will be low.
B. The CRP protein cannot bind to the DNA.
C. If lactose is present, lac mRNA synthesis will occur at a high level.
D. The cell will manufacture glucose by fixing carbon dioxide.
E. The cell will be forced to carry out fermentation.


Regulation of lac mRNA synthesis by intracellular levels of lactose and glucose

The table is a summary of the concepts presented in this problem set on the regulation of lac mRNA synthesis by intracellular levels of lactose and glucose. The relative concentration of cAMP and the relative levels of lac mRNA synthesis in the presence or absence of glucose and lactose are shown.

Glucose cAMP Lactose lac mRNA
present low concentration absent no mRNA
present low concentration present low level of mRNA
absent high concentration absent no mRNA
absent high concentration present high level of mRNA

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Updated: July 15, 1999
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