Switching genes on and off: the lac operon — NEET & JEE Questions

Question 1 · difficulty L1 · recall

The lac operon is classically described as:

• A. a eukaryotic enhancer
• B. constitutive in all conditions
• C. inducible
• D. repressible only

Question 2 · difficulty L2 · understanding

The lac operon in E. coli is an example of

• A. inducible regulation of genes involved in lactose utilisation
• B. constitutive expression of every bacterial gene
• C. eukaryotic RNA splicing
• D. DNA replication control only

Question 3 · difficulty L2 · understanding

In the absence of lactose, the lac repressor normally

• A. binds the operator and blocks transcription
• B. destroys the structural genes
• C. acts as RNA polymerase
• D. binds ribosomes to start translation

Question 4 · difficulty L2 · understanding

When lactose is available, its inducer form binds the lac repressor and

• A. reduces the repressor's ability to bind the operator
• B. makes the repressor bind the operator more strongly
• C. destroys RNA polymerase
• D. removes the promoter from DNA

Question 5 · difficulty L3 · understanding

In the lac operon, the $\boldsymbol{z}$ gene codes for

• A. permease
• B. transacetylase
• C. beta-galactosidase
• D. the repressor of lac operon

Question 6 · difficulty L3 · understanding

Given below are two statements : Statement I: In the lac operon, the z gene codes for beta-galactosidase which is primarily responsible for the hydrolysis of lactose into galactose and glucose. Statement II: In addition to lactose, glucose or galactose can also induce lac operon. In the light of the above statements, choose the correct answer from the options given below :

• A. Statement I is true but Statement II is false
• B. Statement I is false but Statement II is true
• C. Both Statement I and Statement II are true
• D. Both Statement I and Statement II are false

Question 7 · difficulty L3 · understanding

The lactose present in the growth medium of bacteria is transported to the cell by the action of

• A. Beta-galactosidase
• B. Acetylase
• C. Permease
• D. Polymerase

Question 8 · difficulty L3 · understanding

Name the component that binds to the operator region of an operon and prevents RNA polymerase from transcribing the operon.

• A. Promotor
• B. Regulator protein
• C. Repressor protein
• D. Inducer

Question 9 · difficulty L3 · understanding

Which one of the following acts as an inducer for lac operon ?

• A. Sucrose
• B. Lactose
• C. Glucose
• D. Galactose

Question 10 · difficulty L3 · understanding

Match List I with List II. List I List II (A) Gene 'a' (I) $$\beta$$-galactosidase (B) Gene 'y' (II) Transacetylase (C) Gene 'i' (III) Permease (D) Gene 'z' (IV) Repressor protein Choose the correct answer from the options given below :

• A. A-II, B-III, C-IV, D-I
• B. A-III, B-IV, C-I, D-II
• C. A-III, B-I, C-IV, D-II
• D. A-II, B-I, C-IV, D-III