assignment In a study of lac operon, inducers (lactose) are added to a culture o
ID: 267262 • Letter: A
Question
assignment
In a study of lac operon, inducers (lactose) are added to a culture of E. coli at time 0.
After 3 minutes, glucose is added to the bacterial culture. Throughout the course, you will be taken out
Frequent even tests in which you measure the amount of lac mRNA (mRNA encoding ?-galactosidase). Only the fully finished mRNA is included in the analysis.
The figure here shows the measured amounts of lac mRNA as a function of time.
1) What causes glucose addition and what is the underlying mechanism?
2) What is due to the case seen in lac mRNA after approx. 1 minute after the addition of glucose?
3) Explain the curve for the amount of ?-galactosidase protein as a function of time. Give a brief explanation of the course.
Explanation / Answer
1. Lactose is added lac operon is activated resulting in expression of genes for lactose metabolism. Soon, lactose would be consumed so glucose was added as energy source. Glucose addition will again switch off the lac expression.
2. Addition of lactose will activate the lac operon by binding to the repressor protein (inactivating it from lac repression), resulting in expression of genes metabolising lactose as energy source. Lac operon activation results in expression of lac mRNA.
3. Initially when lactose was absent, expression level was low. But on addition of lactose, it binds to repressor protein to inactivate it and hence activates lac expression. Further when glucose is added, expression level decrease since lac operon is repressed. Lac operon is only expressed when lactose is present and glucose is absent. Two regulators turn the operon ON/OFF in response to lactose and glucose levels are the lac repressor and catabolite activator protein (CAP). CAP senses glucose via cAMP and activates transcription when glucose levels are low.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.