Question

Q3 A newly identified bacterial strain needs nedine as a growth factor. To synthesize nedine these bacteria use three enzymes that are encoded by the genes nedA, nedB and nedC in the ned operon. The expression of these three genes is controlled by a regulatory protein NedR. Nedine binds to NedR, and it changes the ability of NedlR to bind to the regulatory region of the ned operon. The ned genes are expressed only in the absence of nedine. The regulator NedR, only when bound to nedine, can bind at the regulatory region of the ned operon.

a. Draw the ned operon showing structural and regulatory genes, the regulatory region including the promoter and terminator. Describe the role of each term in your drawing.

b. Show the regulation model of the ned operon in the absence of nedine. In your figures, include structural genes, regulatory region, NedR, transcription and translation. Describe the process how gene expression is turned ON or OFF in the absence of nedine.

c. Show the regulation model of the ned operon in the presence of nedine. In your figures, include structural genes, regulatory region, NedR, nedine, transcription and translation. Describe the process of how gene expression is turned ON or OFF in the presence of nedine.

d. Answer the following questions and provide an explanation for each answer:
i. Is the ned operon inducible or repressible?
ii. Is the NedR a positive or negative regulator.

e. Predict the expression of the ned operon in the following three nedR mutants nedR1, nedR2 and nedR3. Choose an answer as regulated or constitutive or no expression, including an explanation.
i. In a nedR1 mutant, NedR has lost the ability to bind to nedine.
ii. In a nedR2 mutant, NedR cannot bind to the regulatory region irrespective of the presence or absence of nedine.
iii. In a nedR3 mutant, NedR binds to the regulatory region irrespective of the presence or absence of nedine.

Answer 1

Answer has been explained below

Hope this will help

A)

B)

C)

D) according to the previous answer we can answer following questions

i) this is repeessible operon

When nedicin is present, repress the operon

Nedicin is absent- expression of operon

ii) Ned R is negative regulator

E) in the mutant

i) ned R mutant, where inhibitor protein lost the ability to bind nedicin protein. So nedicin inhibitor will always remain in inappropriate form and will not be able to bond at operator. here RNA polymerase always binds to promoter and cause transcription.

ii) here in this mutant , Ned R is not able to bind at regulatory region so it will also allow expression of operon.

Lead to constitutive expression of operon

iii) here Ned R always binds to operator weather nedicin present or absence. So it will block expression of operon.

So here no expression of operon occur.

So this will lead to constitutive expression of operon

ii)