Explore topic-wise MCQs in Molecular Biology.

This section includes 15 Mcqs, each offering curated multiple-choice questions to sharpen your Molecular Biology knowledge and support exam preparation. Choose a topic below to get started.

1.

Attenuator in the tryptophan operon is the __________

A. Operator sequence
B. Non-transcribed region within the operon
C. Leader sequence for the site of RNA polymerase binding
D. Leader sequence in the tryptophan mRNA coding for many tryptophan residues
Answer» E.
Discussion
2.

Which of the following is false about bacterial tryptophan operon?

A. It has two kinds of regulation system
B. The co-repressor is the catabolite activator protein
C. When tryptophan supply is insufficient the tryptophan operon activates
D. The complex of repressor with co-repressor on binding to the operator blocks transcription
Answer» C. When tryptophan supply is insufficient the tryptophan operon activates
Discussion
3.

In the case of lac operon, the gene expression is inhibited by __________

A. Presence of lactose
B. Interaction of repressor with lactose
C. Interaction of repressor with operator
D. Interaction of lactose with operator
Answer» D. Interaction of lactose with operator
Discussion
4.

Mutation in the regulatory gene of a positively controlled operon can be identified by __________

A. Operon induction
B. Operon repression
C. High expression
D. Constitutive expression
Answer» C. High expression
Discussion
5.

What effect would a loss-of-function mutation have on the expression of the gene encoding the catabolite activator protein of the lac operon?

A. Low expression in the presence of lactose and off in its absence, regardless of the presence or absence of glucose
B. High expression in the presence of lactose and off in its absence, regardless of the presence or absence of glucose
C. Low expression in the presence of glucose and off in its absence, regardless of the presence or absence of lactose
D. High expression in the presence of glucose and off in its absence, regardless of the presence or absence of lactose
Answer» B. High expression in the presence of lactose and off in its absence, regardless of the presence or absence of glucose
Discussion
6.

The complete expression of the lac operon requires __________

A. Lactose
B. Allolactose
C. Lactose and cAMP
D. Allolactose and cAMP
Answer» E.
Discussion
7.

If there is an insertion mutation in the operator of the lac operon, the expression of the lac structural gene will be __________

A. Resistant to catabolic expression
B. Unexpressed
C. Constitutively expressed
D. Permanently disabled
Answer» D. Permanently disabled
Discussion
8.

According to the repressor of lac operon which of the following are false?

A. It is the gene product of the regulatory gene
B. It binds to the promoter region
C. It blocks the transcription of structural genes
D. It combines with allolactose and thus does not bind to the operon
Answer» C. It blocks the transcription of structural genes
Discussion
9.

Lac operon follows a trans-acting control mechanism.

A. True
B. False
Answer» B. False
Discussion
10.

If the lac operon of the genome of bacteria is always active it has a defect in which region of the operon?

A. i
B. o
C. Promoter
D. Structural gene
Answer» B. o
Discussion
11.

Defects in which regions can affect the activity of the lac operon?

A. Promoter
B. i
C. Terminator
D. i and o
Answer» E.
Discussion
12.

How many enzymes are produced in the lac operon under the same promoter?

A. 4
B. 3
C. 2
D. 1
Answer» C. 2
Discussion
13.

Presence of lactose itself induces the production of -galactoside transferase.

A. True
B. False
Answer» B. False
Discussion
14.

The investigation of the lac operon for the metabolism of lactose was done by __________

A. Gilbert
B. Walter Gilbert
C. Francois Jacob and Jacques Monod
D. Walter
Answer» D. Walter
Discussion
15.

The functional unit in which genes are arranged consecutively is known as ___________

A. Induction system
B. An end product repression system
C. A consecutive enzyme system
D. Operon
Answer» E.
Discussion