Water and Biomolecular Interactions Practice Quiz (10 questions)

Explanation

At 25°C, water’s dielectric constant is 78.5 and ethanol’s is 24.3; the higher value reduces attraction between charged particles more. Hexane’s value is 1.9, and water’s high dielectric constant enables it to dissolve large quantities of salts.

Explanation

Hydrogen bonding involves a partially unshielded hydrogen covalently attached to oxygen or nitrogen interacting with a lone pair on another oxygen or nitrogen. Liquid-water molecules associate with an average of 3.5 others, and the bonds are transient with a half-life of a few picoseconds; rupture requires about 4.5 kcal/mol, less than 5% of the energy needed to break a covalent O—H bond.

Explanation

Hydrogen bonding contributes to water’s relatively high viscosity, surface tension, and boiling point. Aldehydes can accept hydrogen bonds through oxygen lone pairs; alcohols and amines can both donate and accept hydrogen bonds, so the latter two statements misstate their roles.

Explanation

Hydrophobic interactions describe nonpolar compounds associating in water, which reduces disruption of favorable water–water interactions. Attraction between oppositely charged groups is a salt bridge, not a hydrophobic interaction.

Explanation

In water, proteins tend to bury hydrophobic amino-acid side chains and expose charged or polar side chains on their surfaces. The reverse arrangement would expose nonpolar groups to water and bury groups that interact favorably with it.

Explanation

Van der Waals interactions between stacked purine and pyrimidine bases help stabilize the DNA double helix. Hydrogen bonds, rather than van der Waals forces, provide the specific interactions between paired bases.

Explanation

Proteases catalyze protein hydrolysis into component amino acids, while nucleases catalyze hydrolysis of phosphoester bonds in DNA and RNA. The reverse pairing is incorrect because it assigns each enzyme’s substrate to the other enzyme.

Explanation

The favorable free-energy change of ATP hydrolysis can offset the unfavorable transfer, so the coupled reaction favors synthesis overall. Enzymes can accelerate approach to equilibrium, but they do not determine the equilibrium point.

Explanation

One water molecule transfers a proton to another, producing hydronium and hydroxide ions. A free hydrogen ion is not the product shown because the proton is accepted by another water molecule.

Explanation

Water has a slightly skewed tetrahedral geometry, with oxygen at the center and a hydrogen–oxygen–hydrogen angle of about 105°, contributing to its asymmetric charge distribution. A linear arrangement would not describe the stated geometry.