Difficulty: Easy
Correct Answer: Increases
Explanation:
Introduction:
The melting temperature (Tm) of DNA is the point at which half of the duplex molecules are denatured. It depends strongly on base composition because GC pairs have three hydrogen bonds and stronger stacking than AT pairs. This question asks for the qualitative direction of Tm change when GC% increases markedly.
Given Data / Assumptions:
Concept / Approach:
Higher GC content typically raises Tm. A common approximation for short DNAs is Tm ≈ 2 °C * (A + T) + 4 °C * (G + C). While exact values depend on length, salt, and sequence context, the direction is unambiguous: more GC → higher Tm.
Step-by-Step Solution:
Verification / Alternative check:
Empirical nearest-neighbor models show positive correlation between GC fraction and Tm across ionic strengths; calibration curves confirm the trend.
Why Other Options Are Wrong:
Common Pitfalls:
Ignoring salt concentration and length when computing exact Tm; here only the qualitative direction is required.
Final Answer:
Increases.
Discussion & Comments