What causes duplex DNA with certain (A+T):(G+C) ratios to melt at higher temperatures than those with greater (A+T):(G+C) ratios?

What causes duplex DNA with certain (A+T):(G+C) ratios to melt at higher temperatures than those with greater (A+T):(G+C) ratios?

• A. Stronger van der Waals forces of pyrimidines
• B. Stronger van der Waals forces of purines
• C. Increased π-stacking strength
• D. Reduced electrostatic repulsion of phosphates

Answer: (C)

Duplex DNA consists of two strands held together primarily by hydrogen bonds between complementary nucleobases (adenine with thymine and guanine with cytosine), as well as stacking interactions among the bases. The melting temperature of DNA, or the temperature at which the strands separate, is influenced by the composition of the bases in the strands. Higher melting temperatures are associated with DNA that contains a higher proportion of guanine and cytosine (G+C pairs) compared to adenine and thymine (A+T pairs). This is mainly because G+C base pairs form three hydrogen bonds compared to the two hydrogen bonds formed by A+T pairs, leading to increased stability of the DNA duplex. The correct answer emphasizes the concept of increased π-stacking strength. π-stacking interactions occur between the aromatic rings of adjacent bases, and in DNA with a higher G+C content, these interactions are enhanced due to the structure and properties of the bases involved. The more stable the stacking interactions, the more energy is required to separate the strands, resulting in a higher melting temperature for the DNA duplex. In contrast, duplex DNA containing a greater proportion of A+T pairs typically represents a less stable configuration due to the weaker interactions relative to G+C pairs. This

Duplex DNA consists of two strands held together primarily by hydrogen bonds between complementary nucleobases (adenine with thymine and guanine with cytosine), as well as stacking interactions among the bases. The melting temperature of DNA, or the temperature at which the strands separate, is influenced by the composition of the bases in the strands.

Higher melting temperatures are associated with DNA that contains a higher proportion of guanine and cytosine (G+C pairs) compared to adenine and thymine (A+T pairs). This is mainly because G+C base pairs form three hydrogen bonds compared to the two hydrogen bonds formed by A+T pairs, leading to increased stability of the DNA duplex.

The correct answer emphasizes the concept of increased π-stacking strength. π-stacking interactions occur between the aromatic rings of adjacent bases, and in DNA with a higher G+C content, these interactions are enhanced due to the structure and properties of the bases involved. The more stable the stacking interactions, the more energy is required to separate the strands, resulting in a higher melting temperature for the DNA duplex.

In contrast, duplex DNA containing a greater proportion of A+T pairs typically represents a less stable configuration due to the weaker interactions relative to G+C pairs. This