Final answer:
Amino acid side chains can be nonpolar, polar but uncharged, acidic, or basic, with each type contributing to the distinct characteristics of the amino acids. Thus, the answer is D) All are correct.
Step-by-step explanation:
Amino acid side chains, also known as R-groups, determine the unique characteristics and functions of each amino acid by contributing to its size, shape, solubility, and ionization properties. These R-groups can be broadly classified into four categories:
- Nonpolar: Side chains that consist of aliphatic or aromatic hydrocarbons which are hydrophobic.
- Polar but uncharged: These include side chains with alcohol or amide groups, which are hydrophilic and can form hydrogen bonds with water but do not ionize.
- Acidic: Side chains that carry a negative charge at physiological pH due to the presence of a carboxylate group.
- Basic: Side chains that carry a positive charge at physiological pH, like those of lysine and arginine.
Therefore, the correct answer is D) All are correct, as amino acid side chains can be nonpolar, polar but uncharged, acidic, or basic.