Lac Operon

Q.

What is Chargaffs rule?

Q.

What are transformants and non-transformants?

Q. Which of the following is true?
(a) Lac operon hypothesis was proposed by Jacob and Monod.
(b) 'One gene-one enzyme hypothesis' was proposed by Beadle and Tatum.
(c) 'Southern blotting' is used in DNA fingerprinting.
(d) Uracil and thymine bases are present in DNA and RNA respectively.

1. Only a, c
2. a, b, c, d
3. Only b, c, d
4. Only a, b, c

Q.

What Is the Lac Z Gene?

Q.

Name the enzyme, which will be produced in a cell in which there is a nonsense mutation in the Lac Y gene?

Q.

Is lac operon repressible or inducible?

Q.

What can happen if the TRP operon is turned on?

Q. Which enzyme/s will be produced in a cell in which there is a nonsense mutation in the lac y gene?

1. Lactose permease
2. Transacetylase
3. Lactose permease and transacetylase
4. $\beta$-galactosidase

Q.

The lac operon consists of

1. Three regulatory genes and three structural genes

2. Two regulatory genes and two structural genes

3. One regulatory gene and three structural genes

4. Four regulatory genes only

Q. Select the incorrect statement given below about lac operon when Lactose is present in the medium.

1. Inducer-Repressor complex is formed
2. Lactose inactivates repressor protein
3. RNA polymerase transcribe Z-gene, Y-gene and A-gene
4. Gene – LacA gets transcribed into mRNA which produces $\beta$ -galactosidase

Q. Components of an operon are

1. Operator, promoter and regulated genes
2. Regulator, promoter, operator and structural genes
3. Operator, regulator and structural genes
4. Regulator, promoter and structural genes

Q. Match the following genes of the Lac operon with their respective products.

a.	i gene	i.	$\beta -$galactosidase
b.	z gene	ii.	Permease
c.	a gene	iii.	Repressor
d.	y gene	iv.	Transacetylase

1. a-iii, b-iv, c-i, d-ii
2. a-i, b-iii, c-ii, d-iv
3. a-iii, b-i, c-ii, d-iv
4. a-iii, b-i, c-iv, d-ii

Q.

Which of the following is required as inducer for the expression of Lac operon?

1. Lactose and Galactose

2. Lactose

3. Galactose

4. Glucose

Q. E. coli cells with a mutated z gene of the lac operon cannot grow in medium containing only lactose as the source of energy because

1. In the presence of glucose, E.coli cells do not utilize lactose
2. They cannot synthesize functional beta galactosidase
3. They cannot transport lactose from the medium into the cell
4. The lac operon is constitutively active in these cells

Q.

What is repressible operon?

Q.

What are the components of lac operon?

Q.

The polycistronic structural gene in lac operon is regulated by?

Q.

Match the following and choose the correct option

A. Capping	I. Association of RNA polymerase with (ρ) factor
B. Tailing	II. Removal of introns
C. Splicing	III. Methyl guanosine triphosphate added to 5’ end of hnRNA
D.Termination	IV. Addition of adenylate residues

1. A-I, B-III, C-II, D-IV
2. A-II, B-I, C-IV, D-III
3. A-III, B-IV, C-II, D-I
4. A-II, B-III, C-IV, D-I

Q.

What is negative regulation?

Q.

Repressor protein is produced by

1. Operator gene

2. Structural gene

3. Regulator gene

4. Promotor gene

Q.

What is positive control in gene expression?

Q. Read the statements regarding the lac operon and choose the correct option
I. An inducer regulates the switching on and off of lac operon.
II.Repressor protein dissociates from operator region and prevents RNA polymerase from transcribing the operon.
III. In the presence of lactose, the repressor is activated by interaction with lactose.
IV. RNA polymerase has access to the promoter and transcription proceeds only when the repressor is inactivated.

1. I and IV are correct
2. Only II is correct
3. III and IV are correct
4. I and III are correct

Q. Describe how the lac operon operates, both in the presence and absence of an inducer in E.coli. [5]

Q. Regulatory gene in lac operon is 'i' gene. i is derived from word ________.

1. Inducer
2. Inhibitor
3. Inheritable
4. None of these

Q.

In , the lac operon gets switched on when

1. Repressor binds to operator

2. Lactose is present and it binds to RNA polymerase

3. Lactose is present and it binds to the repressor

4. RNA polymerase binds to the operator

Q.

In the medium where E. coli was growing, lactose was added, which induced the lac operon. Then, why does lac operon shut down some time after addition of lactose in the medium?

Q.

Why is lac operon an example of gene regulation in response to changes in environmental conditions?

Q.

In the Lac operon system, β-galactosidase is coded by

1. z-gene

2. a-gene

3. y-gene

4. I-gene

Q. Which of the following statements are true about lac operon?
I. Glucose binds to CAP binding site and activates the operon
II. In the absence of lactose, the repressor binds with the operator region
III. All three structural gene products are not essential for the metabolism of lactose
IV. The operator is a negative regulatory site bound by the lac repressor protein

1. II and III
2. I and II
3. II and IV
4. I and III

Q.

How do prokaryotes regulate gene expression?