Question

Hydrogen bonds can form with bases on the opposite DNA strands in the double helix, or between the bases and H2O in the single stranded conformation. Considering that the double helix is the most stable conformation in water, how does this observation support the conclusion that base stacking contributes more to helix stability than interbase hydrogen bonding

Answer 1

The number of hydrogen bonds between complementary nucleotide bases in the double-stranded DNA molecule is nearly equal to the number of hydrogen bonds between nucleotide bases and water, thereby stacking interactions should confer more stability to the double helix

Step-by-step explanation:

Base stacking refers to the arrangement of nucleotide bases found in the tridimensional (3D) structure of nucleic acids in water solution, where hydrophobic bases stack together to exclude water and maximize Van der Waals forces, thus conferring higher stability to the 3D structure. In a DNA molecule, both DNA strands are bonded together by hydrogen bonds, stacking interactions and hydrophobic interactions. Base stacking is the strongest type of interaction between base pairs. In turn, base stacking forces vary depending on the nature of the base pair, being strongest for stacks of guanine-cytosine (G-C) base pairs and weakest for adenine-thymine (A-T) base pairs, it is due to the fact that three hydrogen bonds are formed in G-C base pairs, while only two hydrogen bonds are formed in A-T base pairs.