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NEET Biology · Genetics and Evolution

DNA as genetic material: structure, packaging and replication

Taught in NCERT Class 12 Biology, Chapter 5: Molecular Basis of Inheritance.

4 verified questions: Easy 0 · Medium 4 · NEET level 0

Sample questions

Sample 1Medium

A diagram of a replication fork shows the parental double helix unwinding. On the template strand with polarity 3'→5', new strand A is made in one continuous stretch towards the fork. On the template with polarity 5'→3', new strand B is made as short pieces in the opposite direction, which are later joined. Which statement is correct?

  1. A

    B is continuous and A discontinuous, with pieces joined by helicase

  2. B

    The pieces of B are joined by DNA polymerase, which can also polymerise 3'→5'

  3. C

    A is continuous because DNA polymerase works only in the 5'→3' direction, and the pieces of B are joined by DNA ligase

  4. D

    Both strands are made continuously, so no ligase is needed

Show the answer
The answer is C.

DNA polymerase polymerises only in the 5'→3' direction, so replication is continuous on the 3'→5' template and discontinuous on the 5'→3' template. The discontinuous fragments are later joined by DNA ligase.

  • A.

    The labels are reversed, and helicase unwinds DNA rather than joining fragments.

  • B.

    DNA-dependent DNA polymerases catalyse polymerisation only in the 5'→3' direction.

  • D.

    Only the 3'→5' template is copied continuously; the other is copied discontinuously.

NCERT: Class 12 Biology, Chapter 5, 5.4

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