Two double-stranded DNA samples have identical lengths but different melting temperatures (the temperature at which strands separate). Sample X melts at 78 °C; sample Y melts at 88 °C. A researcher hypothesizes the difference comes from base composition.
Which sample most likely contains a higher percentage of G-C pairs?
- A
Both are equal regardless of composition
- B
Sample Y, because A-T pairs use covalent bonds
- C
Sample X, because A-T pairs are heavier
- Dcheck_circle
Sample Y, because G-C pairs have 3 H-bonds and require more energy to break
Explanation
G-C pairs share three hydrogen bonds vs two for A-T, so DNA richer in G-C is harder to denature and melts at higher temperatures.