Molecular Biology lac Operon MCQs with answer 2023

Here is a compilation of lac operon mcq with answer key for practice . This post consists of Molecular Biology Multiple Choice Questions from the topic lac Operon (Gene regulation & Catabolite Repression) with Answer Key. These questions can be very useful for the preparation of all the competitive examinations in Biology / Life Sciences such as CSIR JRF NET, ICMR JRF, DBT BET JRF, GATE and other University Ph.D Entrance Examinations. So, you can test yourself HERE.

Molecular Biology MCQs with answers lac Operon (Gene regulation & Catabolite Repression) 2022 for CSIR JRF NET, ICMR JRF, DBT BET JRF, GATE and other University Ph.D Entrance Examinations
Molecular Biology lac Operon MCQs with answer 2023

Molecular Biology mcqs on lac operon with answer key:

1. Which of the following acts as the inducer of lac operon is?

(a) Lactose
(b) Allolactose
(c) Galactose
(d) Glucose

Answer

Answer: (b)


2. The sequence of the structural gene in lac operon is:

(a) lacZ – lacY – lacA
(b) lacA – lacY – lacZ
(c) lacZ – lacA – lacY
(d) lacA i- lacZ – lacY

Answer

Answer: (a)


3 If the repressor of the lac operon binds to the operator, it will lead to:

(a) Switch on transcription
(b) Switch off transcription
(c) Enhanced transcription
(d) Differential gene expression

Answer

Answer: (a)


4. If activator binds to the repressor, it will prevent

(a) Transcription
(b) Binding of RNA polymerase to the promoter
(c) Binding of the repressor to the operator
(d) Binding of the repressor to the promoter

Answer

Answer: (b)


5. In the lac operon, under which of the following conditions will the lac genes be transcribed at high levels?

(a) Low glucose, low lactose
(b) High glucose, low lactose
(c) Low glucose, high lactose
(d) High glucose, high lactose

Answer

Answer: (c)


6. The cleavage of X-gal by B galactosidase enzyme produce the blue coloured 5-bromo-4-chloro-3-hydroxy indone and

(a) β-D galactose
(b) α-D galactose
(c) β-L galactose
(d) α-L galactose

Answer

Answer: (a)


7. The gene product of LacA gene in Lac-operon is:

(a) Beta-galactosidase
(b) Beta-galactoside permease
(c) Beta-galactoside transacetylase
(d) Beta-galactoside isomerase

Answer

Answer: (c)


8. The gene product of LacZ gene in Lac-operon is:

(a) Beta-galactosidase
(b) Beta-galactoside permease
(c) Beta-galactoside transacetylase
(d) Beta-galactoside isomerase

Answer

Answer: (a)


9. The lac operon is a:

(a) Negatively regulated operon
(b) Positively regulated operon
(c) Sometimes positive and sometimes negative
(d) None

Answer

Answer: (a)


10. The gene product of Lacy gene in Lac-operon is:

(a) Beta-galactosidase
(b) Beta-galactoside permease
(c) Beta-galactoside transacetylase
(d) Beta-galactoside isomerase

Answer

Answer: (b)


11. A mutation occurs in the lac repressor protein such that it can no longer bind to lactose. What effect will this mutation have on the expression of proteins of the lac operon in the presence of lactose?

(a) It will have no effect since lactose shuts off the operon
(b) It will decrease the expression of the lac operon proteins
(c) It will increase the expression of lac operon proteins
(d) It will have no effect since the operon is modulated by another protein

Answer

Answer: (b)


12. Choose the correct option from the following regarding the lac operon in E. coli?

(a) lac operon is switched on in the absence of lactose
(b) lac operon messenger RNA is a polycistronic mRNA
(c) β-galactosidase is the only enzyme produced in large quantities when the lac operon is switched on
(d) Lac repressor binds to the lac promoter

Answer

Answer: (b)


13. Which of the following genes is not a structural gene of the lac operon?

(a) lacA
(b) lac I
(c) lacY
(d) lacZ

Answer

Answer: (b)


14. The lac operon

(a) Is under negative and positive control
(b) Is under positive control only
(c) Is normally expressed constitutively
(d) Is an example of a tissue-specific expression

Answer

Answer: (a)


15. Pribnow box is the component of

(a) Operators
(b) Promoters
(c) Enhancers
(d) Activators

Answer

Answer: (b)


16. A network of operons with a common regulator is called:

(a) Regulon
(b) Inter-linked operon
(c) Meta-operon
(d) Super-operon

Answer

Answer: (a)


17. Allolactose is a disaccharide of D-galactose and D-glucose linked through:

(a) β1-6 glycosidic linkage
(b) β1-4 glycosidic linkage
(c) β1-2 glycosidic linkage
(d) α1-6 glycosidic linkage

Answer

Answer: (a)


18. Among the following, which statement is correct about the promoter of a gene?

(a) It is always located upstream of transcription start site
(b) It is located downstream of translation start site
(c) Different promoter elements are recognized by different RNA polymerases
(d) Promoters are recognized due to their different secondary structures

Answer

Answer: (c)


19. Lactose permease, the membrane protein which facilitates the transport of lactose from the external medium into the bacterial cell is a:

(a) Symporter
(b) Antiporter
(c) Uniporter
(d) All  of the above

Answer

Answer: (a)


20. Isopropyl B-D-1-thiogalactopyranoside (IPTG) used to induce lac operon in molecular biology experiments is:

(a) A non-hydrolyzable analogue of allolactose
(b) A non-hydrolyzable analogue of lactose
(c) A hydrolysable analogue of allolactose
(d) A hydrolysable analogue of allolactose

Answer

Answer: (a)


21. In a negatively regulated operon the bound repressor will:

(a) Inhibit transcription
(b) Facilitate transcription
(c) Enhance the enzymatic activity of RNA polymerase
(d) Decrease the enzymatic activity of RNA polymerase

Answer

Answer: (a)


22. The functional lac repressor is a:

(a) Dimer of identical monomers
(b) Trimer of identical monomers
(c) Tetramer of identical monomers
(d) Tetramer of two identical dimers

Answer

Answer: (c)


23. The transcription of lac repressor from the I gene is:

(a) Independent of lac operon genes
(b) Dependent on lac operon genes
(c) Dependent on lactose concentration in the cell
(d) Dependent on glucose concentration in the cell

Answer

Answer: (a)


24. The number of secondary binding site(s) for the lac repressor in the lac operon is:

(a) 1
(b) 2
(c) 3
(d) 4

Answer

Answer: (b)


25. The fundamental characteristic of the CRP-CAMP complex and lac repressor in lac operon is:

(a) CRP-CAMP is a positive regulatory element while lac repressor is a negative regulatory element
(b) CRP-CAMP is a negative regulatory element while lac repressor is a positive regulatory element.
(c) Both CRP-CAMP and lac repressors are positive regulatory elements
(d) Both CRP-CAMP and lac repressors are negative regulatory elements.

Answer

Answer: (a)


26. In the absence of glucose, the binding of CRP-cAMP complex to the region near to the lac promoter will:

(a) Decrease transcription of lac genes
(b) Increase transcription of lac genes
(c) No significant effect on the transcription of lac genes.
(d) Cause the release of RNA polymerase from the promoter

Answer

Answer: (b)


27. The strong induction of lac operon is favoured by:

(a) Presence of lactose, absence of glucose and in increased concentration of CRP-cAMP complex
(b) Presence of lactose, presence of glucose and increased concentration of CRP-CAMP complex
(c) Presence of lactose, absence of glucose and decreased concentration of CRP-CAMP complex
(d) Presence of lactose, presence of glucose and decreased concentration of CRP-cAMP complex

Answer

Answer: (a)


28. What will happen when E. coli cells are grown in a medium containing both glucose and lactose?

(a) Both CAP and the lac repressor are bound to the DNA.
(b) CAP is bound to the DNA but the lac repressor is not
(c) Lac repressor is bound to the DNA but CAP is not.
(d) Neither CAP nor the lac repressor is bound to the DNA.

Answer

Answer: (d)


29. The lac repressor has which of the following DNA-binding motif ?

(a) Helix-turn-helix
(b) Zinc finger
(c) Homeodomain
(d) Leucine zipper

Answer

Answer: (a)


30. The absence of which of the following component will deduce the expression of lac structural gene?

(a) lacl gene product
(b) CAMP
(c) Allolactose and lactose
(d) Adenylate cyclase

Answer

Answer: (a)


Wrap up:

Hope you like the MCQ above regarding Molecular Biology MCQs with answers of lac Operon 2023 helpful for for CSIR JRF NET, ICMR JRF, DBT BET JRF, GATE and other University Ph.D Entrance Examinations . If you have any other queries , feel free to reach us so that we can revert back to us at the earliest possible.

And if any answer is wrong then feel free to correct us 🤗.

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