Biochemistry Questions and Answers – DNA Supercoiling

This set of Biochemistry Multiple Choice Questions & Answers (MCQs) focuses on “DNA Supercoiling”.

1. The phenomenon of twisting around itself by a molecule to relieve helical stress is ____________
a) Supercoiling
b) Coiling
c) Elongation
d) Compression
View Answer

Answer: a
Explanation: The phenomenon of twisting around itself by a molecule to relieve helical stress is supercoiling.

2. When there is no net bending of the DNA axis upon itself, the DNA is said to be in a ____________
a) Elongated state
b) Compressed state
c) Relaxed state
d) Denatured state
View Answer

Answer: c
Explanation: When there is no net bending of the DNA axis upon itself, the DNA is said to be in a relaxed state.

3. Over-twisting of a molecule results in ____________
a) Negative supercoiling
b) Positive supercoiling
c) Elongation
d) Compression
View Answer

Answer: b
Explanation: Extra helical twisting leads to positive supercoiling, while subtractive twisting leads to negative supercoiling.
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4. Changing twist from the relaxed state requires adding energy and increases the ____________
a) Forces in molecule
b) Stress along molecule
c) Strain over molecule
d) None of the above
View Answer

Answer: b
Explanation: Relaxed state is the condition at which there is no net DNA bending, changing twist from this state requires additional energy and increases the stress along the molecule.

5. The enzyme responsible for the removal of supercoiling in replicating DNA ahead of the replication fork is ____________
a) Topoisomerase
b) Primase
c) DNA polymerase
d) Helicase
View Answer

Answer: a
Explanation: The enzymes that increase or decrease the extent of DNA under-winding are topoisomerases.

6. The type of topoisomerases which generally relaxes DNA by removing negative supercoiling?
a) Type I
b) Type II
c) Type III
d) Type IV
View Answer

Answer: a
Explanation: Type II enzymes can introduce negative supercoils.

7. The type of topoisomerases that can introduce negative supercoils is ____________
a) Type I
b) Type II
c) Type III
d) Type IV
View Answer

Answer: b
Explanation: Type I generally relaxes DNA by removing negative supercoiling.
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8. The type I enzyme(s) is/are ____________
a) Topoisomerases I and III
b) Topoisomerases II
c) Topoisomerase IV
d) Topoisomerases I and IV
View Answer

Answer: a
Explanation: Generally type I enzymes are topoisomerases I, III and type II enzymes are topoisomerase II.

9. Under-winding is measured in terms of ____________
a) Supercoiling
b) Linking difference
c) Positive supercoiling
d) Negative supercoiling
View Answer

Answer: b
Explanation: Under-winding is measured in terms of specific linking difference, σ also called super helical density.
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10. Which type of supercoiling takes the form of extended right-handed coils?
a) Plectonemic supercoiling
b) Solenoidal supercoiling
c) Negative supercoiling
d) Positive supercoiling
View Answer

Answer: a
Explanation: Solenoidal (negative) supercoiling takes the form of tight left-handed turns about an imaginary tube-like structure whereas plectonemic supercoiling takes the form of right-handed coils.

Sanfoundry Global Education & Learning Series – Biochemistry.

To practice all areas of Biochemistry, here is complete set of 1000+ Multiple Choice Questions and Answers.

If you find a mistake in question / option / answer, kindly take a screenshot and email to [email protected]

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Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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