Question

Name three intermolecular forces that stabilize the structure of DNA, and explain how they act. A. flat, N-containing bases stack above each other, forming ion-dipole bonds to aqueous surroundings B. nitrogen bases form hydrogen bonds to their complementary bases C. sugar-phosphate chains form ion-dipole and hydrogen bonds to the aqueous surroundings D. sugar-phosphate chains form ion-dipole and hydrogen bonds to the nitrogen bases E. flat, N-containing bases stack above each other, forming intrachain hydrogen bonds F. sugar-phosphate chains form hydrogen bonds to the nitrogen bases G. nitrogen bases interact with their complementary bases through dispersion forces H. nitrogen bases form ion-dipole bonds to their complementary bases I. flat, N-containing bases stack above each other, allowing for interaction through dispersion forces J. sugar-phosphate chains stack above each other, allowing for interaction through dispersion forces

Answer 1

DNA is stabilized by hydrogen bonding between complementary bases, van der Waals forces between stacked nitrogenous bases, and hydrogen bonds and ion-dipole interactions between the sugar-phosphate backbone and the aqueous environment.

Step-by-step explanation:

The structure of DNA is stabilized by three important types of intermolecular forces:

1. Hydrogen bonding occurs between the nitrogenous bases on the interior of the DNA helix. Complementary base pairs such as adenine (A) with thymine (T) and cytosine (C) with guanine (G) form hydrogen bonds, which are responsible for the specific pairing and high fidelity of DNA replication. These hydrogen bonds maintain the uniform shape of the DNA double helix, likened to the steps of a spiral staircase.
2. Van der Waals (dispersion) forces act between the flat, nitrogen-containing bases when they stack above each other. These interactions contribute to the overall stability of the DNA molecule by optimizing the distance between the strands and minimizing the energy of the configuration.
3. Hydrogen bonds and ion-dipole interactions also occur as part of the interaction between the sugar-phosphate backbone and the aqueous environment. These interactions help stabilize the outer structure of DNA and its solubility in water.

Answer 2

B. nitrogen bases form hydrogen bonds to their complementary bases

C. sugar-phosphate chains form ion-dipole and hydrogen bonds to the aqueous surroundings

J. sugar-phosphate chains stack above each other, allowing for interaction through dispersion forces

Step-by-step explanation:

B) The hydrogen bonding between complementary base pairs is such that the most energetically stable DNA configuration is achieved when adenine pairs with thymine and guanine pairs with cytosine. Thus although the spatial requirements of B-DNA potentially allow four complementary base pairs to be formed (i.e., G-T, G-C, A-T, and A-C), only the G-C and A-T base pairs are normally found in DNA.

C) The basic structure of DNA can be divided into two portions: the external sugar-phosphate backbone, and the internal bases. The sugar-phosphate backbone, as its name implies, is the major structural component of the DNA molecule. The backbone is constructed from alternating ribose sugar and phosphate molecules which are highly polar. Because the backbone is polar, it is hydrophillic which means that it likes to be immersed in water.

J. The anionic phosphate groups interact electrostatically with each other, and through ion-pi interactions with the aromatic ring sugars and nucleobases. When a guanidinium cation is present, the anionic phosphate group has been reduced to a dipole, and the tuning of denticity tunes the dipole magnitude and orientation. The electrostatic ion-ion interactions of the phosphate groups are reduced to ion-dipole interactions, and the interactions with the aromatic sugars and nucleobases are likewise modified to have a larger contribution from non-electrostatic London dispersion forces