Biochemistry Questions and Answers – DNA Supercoiling

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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.
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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.

4. Changing twist from 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 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.
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6. The type of topoisomerases which generally relaxes DNA by removing negative supercoiling is
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.

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.

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.
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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer & SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage, Advanced C Programming, SAN Storage Technologies, SCSI Internals & Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him @ LinkedIn