AP BIOLOGY

Detailed explanation-1: -G-C base pairs have 3 hydrogen bonds, while A-T base pairs have two. Therefore, double-stranded DNA with a higher number of G-C base pairs will be more strongly bonded together, more stable, and will have a higher melting temperature.

Detailed explanation-2: -DNA is usually found in aqueous solutions both in vivo and in vitro. Since DNA is stable at temperatures below 100°C [as evident in polymerase chain reactions (PCR), for example (Bartlett and Stirling, 2003)], its degradation at higher temperatures cannot be easily tested in aqueous so-lutions.

Detailed explanation-3: -Thus, in Watson et al. (30) we read: ‘Because each CG base pair is held together by 3 hydrogen bonds rather than the two holding each AT base pair, higher temperatures are necessary to separate CG-rich strands than to break apart AT-rich molecules’.

Detailed explanation-4: -The helical structure of double-stranded DNA is destabilized by increasing temperature. Above a critical temperature (the melting temperature), the two strands in duplex DNA become fully separated. Below this temperature, the structural effects are localized.