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With the help of a schematic… (Class 12 Biology 2023, Q22)

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BiologyCBSE Class 12 · Board exam 2023, set 57/1/1 · 3 marks · Short answer

CBSE Class 12 Biology 2023: question 22

Set in the CBSE Class 12 board exam of 2023, paper 57/1/1, section C, question 22, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q22 · 3 marks · Short answerBiotechnology: Principles and Processes

With the help of a schematic diagram only, show in three steps, the formation of recombinant DNA by the action of restriction endonuclease – EcoRI and DNA ligase.

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

Hints

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

Hint 1

EcoRI recognises a 6-base palindrome; write it on both strands.

Hint 2

Where does EcoRI cut, and what kind of ends result?

Hint 3

Which enzyme joins the fragments once their ends pair?

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. Step 1 – Recognition (diagram): Draw the vector DNA (plasmid) and the foreign DNA. Mark on each the palindromic EcoRI site –GAATTC– / –CTTAAG–. Label 'EcoRI recognition site'.

    1 mark

  2. Step 2 – Cutting (diagram): Show EcoRI cutting each strand between G and A. This leaves single-stranded overhangs –AATT– (sticky ends) on both the vector and the foreign DNA fragment. Label 'sticky ends'.

    1 mark

  3. Step 3 – Joining (diagram): Show the complementary sticky ends of the foreign DNA pairing with those of the opened vector. DNA ligase seals the nicks (phosphodiester bonds). Label the product 'recombinant DNA'.

    1 mark

Answer: Schematic: EcoRI recognises GAATTC in vector and foreign DNA → cuts between G and A to give AATT sticky ends → sticky ends anneal and DNA ligase seals them → recombinant DNA

Where the marks are

  • Recognition site GAATTC shown on vector and foreign DNA, labelled (1 mark)
  • Cut between G and A giving sticky ends on both DNAs (1 mark)
  • Annealing of sticky ends and sealing by DNA ligase to form recombinant DNA, labelled (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 57/1/1: 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.