Supercoiling of DNA
Q. 1 True about DNA supercoiling is all except:
| A |
Underwinding results in negative superhelical density & supercoiling |
|
| B |
Superhelical density depends on the length of DNA |
|
| C |
Underwinding strain is normally accommodated by strand separation |
|
| D |
Both B and C. |
Q. 1
True about DNA supercoiling is all except:
| A |
Underwinding results in negative superhelical density & supercoiling |
|
| B |
Superhelical density depends on the length of DNA |
|
| C |
Underwinding strain is normally accommodated by strand separation |
|
| D |
Both B and C. |
Ans.
D
D
Explanation:
- Supercoils are introduced when a closed circle is twisted around its own axis or when a linear piece of duplex DNA, whose ends are fixed, is twisted. This energy-requiring process puts the molecule under torsional stress, and the greater the number of supercoils, the greater the stress
- Negative supercoils are formed when the molecule is twisted in the direction opposite from the clockwise turns of the right-handed double helix found in B-DNA.
- The energy required to achieve this state is stored in the supercoils. One such transition is strand separation, which is a prerequisite for DNA replication and transcription.
Q. 2
DNA supercoiling is done by :
| A |
DNA polymerase I |
|
| B |
DNA polymerase II |
|
| C |
DNA topoisomerase |
|
| D |
DNA gyrase |
Ans.
Explanation:
D i.e. DNA gyrase
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