Question

A. answer the following question in full sentence

J. Monodo and F. Jacob, constructed several mutant strain to study lac operon. which binding domains were affected by lac- and lacIs, and what was the effect of those mutations? how did LacOc affect binding?

B. choose the correct choice in the next 6 multiple-choice questions.

1.FGFR3 mutation causes Achondroplasia, the mutation results in....

a) expression of the gene at an inappropriate place.

b) expression of a gene that is more efficient than WT.

c) inhibition of gene expression

d) expression of a gene with lower dosage compared to WT.

2. Which of these mutants will not produce B-galactosidase in the presence of inducer

a) lacIs

b) Lacl-

c) All of the above

d) lacOc

3. First trans-acting factor to bind to the promoter is

a) RNA polymerase

b) TBP

c) Activator

d) TAF

4. In Benzer’s experiment, he noticed that rll mutant had

a) No plaque formation on E.coli strain k ()

b) Large distinct plaques when grown on e.coli strain k ()

c) No plaque formation on E.coli formation strain B.

d) Small fuzzy plaques when grown on E.coli strain B.

5. Which of these changes in the following sequence will result in a conservative mutation 5’ AAG3’

a) All are correct

b) 5’GAG3’

c) 5’ AGG3’

d) 5’ UAG3’

6. Post-translational modification that results in multiple smaller polypeptides is an example of:

a) Polyprotein processing

b) N- terminal Met removal

c) Phosphorylation

d) Zymogen activator

Answer 1

A) lac operon involves utilization of lactose by bacteria .

Normal when glucose is present- lac operon is repressed .

But glucose is absent and lactose present- induction of lac operon , synthesis of beta galactosidase which degrade lactose and utilized for energy.

LaC I gebe code for inhibitor protein, these protein after teteamerization binds to operator site , prevent binding of RNA polymerase this prevent expression of lac operon gene. This Lac I protein has two domain ,

--one DNA binding domain - through which I pritein bind to DNA

--- second is teteamerization domain, through which tetramerize.

- lactose binding domain, here lactose binds and inhibits it binding to operator

i) Lac I - there is mutation in DNA binding domain, that it is not able to bind to operator, leads to expression of lac operon.

ii) Lac S , known as super repressor, here mutation in lactose binding domain. That presence or absence of lactose will not affect its binding. Now inhibitor protein always binds to operator and repressed Lac operon.

iii) Lac O c  - it denotes constitutive operator. Here mutatiin in inhibitor binding part of operator occur that it will not bind to inhibitor protein and leads to constitute expression of lac operon.

B)

2) option a, Lac S

Super repressor always bind to operator, either in presence or absence of lactose and supress expression of lac operon

3) option B, TBP

First transcription factor which binds to promoter is TF II D, it has two parts TBP and TAFs .

TBP IS THE PROTEIN which bind to promoter first.

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