Lesson eLearning

A primer of 25 bases contains 8 adenine/thyminine (A/T) bases and 17 guanine/cytosine (G/C) bases. How many hydrogen bonds are formed between the primer and its template strand during annealing?

easy MCQ 1 mark Class 12 · Chemistry · Biomolecules
  1. 59
  2. 67
  3. 73
  4. 85
Answer
67

The correct answer is 67 — Add the two contributions: 16 + 51 = 67 hydrogen bonds in total.

Step-by-step solution

  1. Identify that each A/T pair forms 2 hydrogen bonds.
  2. Identify that each G/C pair forms 3 hydrogen bonds.
  3. Multiply: 8 × 2 = 16 hydrogen bonds from A/T pairs.
  4. Multiply: 17 × 3 = 51 hydrogen bonds from G/C pairs.
  5. Add the two contributions: 16 + 51 = 67 hydrogen bonds in total.
Common mistake: Using 2 bonds for every pair or forgetting that G/C pairs form 3 bonds

Concept tested: Base‑pair hydrogen bonding in nucleic acids

Published · How this solution was prepared and checked

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