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Given below is the restriction… (Class 12 Biology 2023, Q8)

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BiologyCBSE Class 12 · Board exam 2023, set 57/5/1 · 1 mark · MCQ

CBSE Class 12 Biology 2023: question 8

Set in the CBSE Class 12 board exam of 2023, paper 57/5/1, section A, question 8, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q8 · 1 mark · MCQBiotechnology: Principles and Processes

Given below is the restriction site of a restriction endonuclease Pst-I and the cleavage sites on a DNA molecule.

5' C-T-G-C-A ↓ G 3'
3' G ↑ A-C-G-T-C 5'

(The arrows mark the cleavage sites: on the upper strand between A and G, on the lower strand between G and A.)

Choose the option that gives the correct resultant fragments by the action of the enzyme Pst-I.

  1. (A)5' C-T-G C-A-G 3'
    3' G-A-C-G-T C 5'
  2. (B)5' C-T G-C-A-G 3'
    3' G-A-G-C T-C 5'
  3. (C)5' C-T-G-C A-G 3'
    3' G-A-C-G T-C 5'
  4. (D)5' C-T-G-C-A G 3'
    3' G A-C-G-T- C 5'

Figure in the paper: Restriction site of Pst-I on double-stranded DNA with two arrows showing cleavage positions on the two strands. Options show pairs of resulting fragments. See it in the official paper.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2023 board paper, set 57/5/1.

Hints

Open one hint at a time and try again before the next.

Hint 1

Cut each strand exactly at the position of its arrow.

Hint 2

On the top strand, the cut leaves G on its own at the 3′ end.

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

  1. Pst-I cuts the upper strand between A and G, giving 5′ CTGCA and G 3′.

    ½ mark

  2. It cuts the lower strand between G and A, giving 3′ G and ACGTC 5′. The resulting fragments match option (D).

    ½ mark

Answer: (D)

Where the marks are

  • Correct fragments, option (D) (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Biotechnology: Principles and Processes, one at a time, marked against the answer key and marking points.Back to the full paper2023 board paper, set 57/5/1: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.