Final answer:
The side group, or R group, of an amino acid is responsible for the differences in size, shape, and electrical charge among amino acids, significantly affecting their role in protein structure and function.
Step-by-step explanation:
The side group, or R group, makes AA differ in size, shape, and electrical charge. Each amino acid's R group influences its unique characteristics, which includes variations in size, shape, solubility, and ionization properties. This diversity in the side chains is crucial as they determine the amino acids' chemical properties, and in turn, influence the overall structure and function of proteins. Proteins' structures are critical as they are closely related to their function within biological systems.