Question

1) Which of the following conditions is most likely to cause the lactose operon to be transcribed? A) There is more glucose in the cell than lactose. B) There is glucose but no lactose in the cell. C) The cyclic AMP and lactose levels are both high within the cell. D) The CAMP level is high and the lactose level is low. 2) How does the transcription of structural genes in an inducible operon occur? A) It occurs continuously in the cell. B) It starts when the pathway's substrate is present. C) It starts when the pathway's product is present. D) It stops when the pathway's product is present. 3) For a repressible operon to be transcribed, which of the following conditions must occur? A) A corepressor must be present. B) RNA polymerase and the active repressor must be present. C) RNA polymerase must bind to the promoter, and the repressor must be inactive. D) RNA polymerase must not occupy the promoter, and the repressor must be inactive. 4) Altering patterns of gene expression in prokaryotes would most likely serve an organism's survival by___ A) organizing gene expression, so that genes are expressed in a given order B) allowing each gene to be expressed an equal number of times C) allowing an organism to adjust to changes in environmental conditions D) allowing environmental changes to alter a prokaryote's genome 5) In positive control of several sugar metabolism-related operons, the CAMP receptor protein (CRP) binds to DNA to stimulate transcription. Which of the following environmental conditions causes an increase in CRP activity in stimulating transcription? A) an increase in glucose and an increase in CAMP B) a decrease in glucose and an increase in CAMP C) an increase in glucose and a decrease in CAMP D) a decrease in glucose and a decrease in the repressor

Answer 1

1.

C) The cyclic-AMP and Lactose levels are both high within the cell.

High cyclic-AMP levels indicate that Glucose levels in the cell are low. When Glucose concentration in the cell is low, cyclic-AMP (cAMP) levels are high and the CRP protein is able to bind to a control element upstream of the Lac Operon Promoter. The presence of Lactose releases the bound LacI from the Operator sequence and transcription can commence.

2)

B) It starts when the pathway's substrate is present.

The Lac Operon is an inducible Operon. It is activated when Lactose is present in the cell.

3)

C) RNA Polymerase must bind to the must bind to the Promoter and the repressor must be inactive.

Transcription of a Repressible Operon may only occur when the Repression molecule is absent and RNA Polymerase is bound to the Promoter and is able to transcribe the Operon.

4)

C) allowing an organism to adjust to changes in environmental conditions.

Alternation in Gene expression patterns of all living organisms is dependent on changing environmental conditions. Organisms tend to adopt expression patterns that allow for survival while spending the least amount of energy.

5)

B) An decrease in Glucose and increase in cAMP

CRP responds to high cAMP levels by binding to binding sites upstream of Operon Promoter which promote RNA Polymerase loading onto the Promoter. This occurs when Glucose is low and alternate energy sources are required by the cell.