A short DNA segment has the template strand sequence 5'-ATGCCGTA-3'. How many hydrogen bonds are formed between this template strand and its newly synthesized complementary strand?
Answer
20 hydrogen bonds
The correct answer is 20 hydrogen bonds — Thus, the newly formed strand is held to the template by 20 hydrogen bonds.
Step-by-step solution
- Write the complementary bases: A pairs with T (2 H‑bonds) and G pairs with C (3 H‑bonds).
- List the base pairs from 5' to 3' of the template: A‑T, T‑A, G‑C, C‑G, C‑G, G‑C, T‑A, A‑T.
- Calculate hydrogen bonds for each pair: A‑T = 2, T‑A = 2, G‑C = 3, C‑G = 3, C‑G = 3, G‑C = 3, T‑A = 2, A‑T = 2.
- Add them: 2+2+3+3+3+3+2+2 = 20.
- Thus, the newly formed strand is held to the template by 20 hydrogen bonds.
Common mistake: Counting two hydrogen bonds for every A‑T pair and three for every G‑C pair, but forgetting to apply it to each individual base.
Concept tested: Base‑pair hydrogen bonding
Published · How this solution was prepared and checked
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