In the following points, I have summarized Lac operon in Ecoli. I need to check

Question

In the following points, I have summarized Lac operon in Ecoli. I need to check if this is on the right track? and where does 'cleavage of disaccharides' fit into this picture?

Lactose is a disaccharide and the bacteria need specific genes to manage catabolism

1) The lacl promotor gene synthesis the repressor protein which binds to the operator gene stopping the RNA polymerase from coding the lac operon genes

2)But when lactose is present, it needs the specific genes to catabolise lactose

3) So, When allolactose (a derivative of lactose)is present, it binds to the repressor protein, the repressor releases from the operator gene

4) This allows the RNA polymerase can attach to the DNA control region

5) And drive down the operon for transcription and induction of the enzyme lacZ(beta-galactosidase) lacY and lacA which breaks lactose down into glucose and galactose

6) When the lactose is all gone, the repressor returns to the operator in a feedback loop system

Explanation / Answer

Summary is done well , needs only some little changes.

Lac operon helps in transcribing genes for producing lactose.This lactose is then transported to cytosol and converted to glucose.Glucose is then used to make energy.cAMP plays major role in regulation of operon.When glucose level are low cAMP level increases and activates CAP(catabolic activator proteins) to transcribe lac genes

1)Lac l gene (regulatory gene for lac operon)(not promoter gene) produces a repressor protein that blocks RNA polymerase from binding to promoter of the operon.Protein formed by the lac l gene is lac repressor.

------>cAMP---RNA polymerase------>------>------>low glucose,lactose available

lac gene expression

------->cAMP---Repressor protein-------x----------x---------xhigh glucose,lactose not available

No expression of lac gene

2)When lactose is present lac genes expressed because allolactose prevents binding of lac repressor to the operator.When lactose is absent,the repressor binds to the operator and prevents transcription.

Table to summerise the regulation:

3)Allolactose prevents binding of repressor proteins with operators.Repressors are released from lac repressor gene and not from operator gene.

4)Lac operon is a piece of DNA which contains several genes involved in lactose metabolism.The Lac operon is a piece of DNA containing several genes involved in the metabolism of lactose.

Now coming to the point of cleavage of disaccharides: Lactose is a disaccharide sugar.

Clevage of this disaccharide lactose(i.e. hydrolysis) to form glucose and galactose.

Lactose + H2O ---------> beta D-galactose + glucose

Lac Z gene transcription leads to formation of beta-galactosidase will cleave lactose into galactose and glucose.

5) Regulation : There are two regulators Positive and negative regulators.

Negative regulator is the repressor protein which binds with allolactose and deactivated.Positive regulator cAMP promoted when glucose level is low but lactose is present.Then cells will catabolise lactose to produce glucose.

Glucose Lactose Repressor Transcription Present Absent Binds No transcription Present present does not binds low level transcription Absent Absent Binds No transcription Absent Present Does not binds Strong transcription

Related Questions

Navigate

• Browse (All)
• Browse I
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.