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In a PCR reaction, primers of 20 bases anneal to the template strand. If 10 of the primer bases are A or T and the remaining 10 are G or C, how many hydrogen bonds are formed between primer and template during annealing?

hard MCQ 4 marks Class 12 · Chemistry · Biomolecules
  1. 30
  2. 40
  3. 50
  4. 60
Answer
50

The correct answer is 50 — Therefore 50 hydrogen bonds are formed during annealing.

Step-by-step solution

  1. Count hydrogen bonds per base pair: AT pairs have 2 H‑bonds, GC pairs have 3 H‑bonds.
  2. There are 10 AT pairs: H‑bonds.
  3. There are 10 GC pairs: H‑bonds.
  4. Add them: H‑bonds.
  5. Therefore 50 hydrogen bonds are formed during annealing.
Common mistake: Assuming all base pairs have the same number of hydrogen bonds

Concept tested: Hydrogen bonding in DNA primers

Published · How this solution was prepared and checked

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