The gene machine program shows you what happens when lactose is present in E col

Question

The gene machine program shows you what happens when lactose is present in E coli, and how the lac operon is under negative control However, the lac operon is also under positive control from a protein called CRP, cAMP Receptor Protein. The absence of the lac repressor is essential but not sufficient for effective transcription of the lac operon. RNA polymerase also depends on the presence of CRP. Like the lac repressor, which can hind to the DNA and lactose, CRP also has two types of binding sites: a site that binds to the DNA near the promoter, and a site thai binds to cAMP. cAMP (cyclic AMP) is a signal moleculc whose concentration in the cell is inversely proportional to that of glucose. cAMP is created from ATP by the enzyme adenylyl cyclase and is used as an intercellular signaling moleculc lo regulate sugar and lipid metabolism. When glucose is present, E. coli will always prefer to metabolize glucose, but when glucose levels are cAMP levels will begin to increase and the CRP-cAMF complex levels will rise. The CRP-cAMP complex will bind to the CRP binding site on the DNA upstream of the lac operon where it will increase the expression of the lac operon genes by enhancing the binding of RNA polymerase to the promoter sequence. Using the figure above, explain why RNA polymerase is not bound to the prometer when both laetose and glucose is present. Explain why the lac operon if Off when neither glucose or lactose is present, even yjough RNA polymerase is bound to the promoter. The tac operon is under negative (the repressor) and positive (CRP) control. Why do you think this is? Why would this be beneficial?

Explanation / Answer

Answers: -

1.when glucose and lactose are present, lac Operon do not turn on and RAN polymerase can not bind to lac Operon promoter because of glucose concentrations.

**If glucose is present cAmp concentration will be less,if cAMP is less CRP-cAMP complex will be low or absent.

** In absence of CRP-cAMP COMPLEX RNA POLYMERASE cannot bind to promoter sequence in lac Operon.

2.If Glucose absent, lactose absent: No transcription of the lac operon occurs.

**cAMP levels are high because glucose levels are low, so CAP is active and will be bound to the DNA.

**However, the lac repressor will also be bound to the operator (due to the absence of allolactose), acting as a roadblock to RNA polymerase and preventing transcription.

3.lactose can be an excellent meal for E. coli bacteria. However, they'll only gobble up lactose when other, better sugars – like glucose – are unavailable.

**The lac operon is an operon, or group of genes with a single promoter (transcribed as a single mRNA). The genes in the operon encode proteins that allow the bacteria to use lactose as an energy source.

**E. coli bacteria can break down lactose, but it's not their favorite fuel.

**If glucose is around, they would much rather use that. Glucose requires fewer steps and less energy to break down than lactose.

**However, if lactose is the only sugar available, the E. coli will go right ahead and use it as an energy source.

**To use lactose, the bacteria must express the lac operon genes, which encode key enzymes for lactose uptake and metabolism.

**To be as efficient as possible, E. coli should express the lacoperon only when two conditions are met:

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