PCB 3063 Lecture Notes - Lecture 39: Lac Operon, Adenylyl Cyclase, Allolactose

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tanwasp406

3 Apr 2018

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What are the control regions of lac operon and their function? laci (i gene): codes for the repressor protein lacp (promotor): binding site for rna polymerase laco (operator): binding site for the repressor protein. The repressor binds to the laco site, preventing the binding of the rna polymerase. Allolactose binds to the repressor, preventing it from binding to the laco. What is the effect of glucose levels on cap activity: low glucose levels induces adenylate cyclase activity (which catalyzes the hydrolysis of atp into camp. + pp: cytoplasmic levels of camp (catabolite) increases, camp activates cap, activated cap facilitates the binding of rna polymerase to the lac promoter. What is necessary to bind rna polymerase to promoter in lac operon when glucose levels are low or. 1. camp levels decrease, cap is inactivated: rna polymerase does not bind to promotor, operon is off. Present- structural genes are turned off by trp itself.

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When (glucose, lactose) ___________ levels inside a bacterial cell are low, cyclicAMP levels are (high, low) __________. This is because metabolizes sugars (activate, inhibit) ___________ the enzyme adenylate cyclase, and (activate, inhibit) __________ the enzyme cAMP phosphodiesterase, causing cyclic AMP levels to rise. Consequently, the CAP protein is (Activated, inhibited, unaffected) ___________ by the cyclic AMP and binds to the lac promoter region, and the CAP protein acts like a sigma factor recruiting (DNA, RNA) ___________ polymerase to the promoter. This establishes condition that may lead to the (transcription, replication) __________ of the lac operon if (allolactose, glucose, lactose) _____________ is available to bind to (lac repressor, lacZ, lacY, lacA) _________ protein keeping this protein from binding to the (lacO, lacZ. lacY, lacA) ___________ gene.

yellowwasp623

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

1.)A.)The lac operon is inducible by the presence of lactose. Loss-of-function mutations in the lacI gene, which encodes the lac repressor (pick all that apply):

A.)slow down the isomerization of lactose into allolactose
B.)decrease the amount of permease activity in the cell in the presence of lactose.
C.)prevent loss-of-function lacZ mutations from making the lac operon uninducible
D.)are recessive to wild type

B.)Mutations that eliminate the lacO operator site (pick all that apply):

A.)slow down the isomerization of lactose into allolactose
B.)decrease the amount of beta-galactosidase in the cell in the presence of lactose
C.)prevent lacS superrepressor mutations from making the lac operon uninducible
D.)are recessive to wild type

C.)Loss-of-function mutations in the lacZ gene, which encodes beta-galactosidase (pick all that apply):

A.)slow down the isomerization of lactose into allolactose
B.)decrease the amount of permease activity in the cell in the presence of lactose
C.)prevent lac repressor from binding the lacO operator site
D.)prevent IPTG from inducing the lac operon

D.)You are studying the Tory operon, which encodes the TorA and TorB genes, and is normally inducible by Torose. You find a mutation, m1, that causes the Tory operon to be uninducible. You examine the merodiploid (m1 TorA+ TorB-)/(+ ToryA- TorB+) and find that Tor A is uninducible and TorB is inducible. You conclude that:

A.)m1 acts in cis
B.)m1 acts in trans

ivorydog394

PCB 3063 Lecture Notes - Lecture 39: Lac Operon, Adenylyl Cyclase, Allolactose

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