Each amino acid differs from others in the: a. chemical structure of the R group. b. size of the amino group. c. number of carboxyl groups d. number of peptide bonds in the molecule.
The correct answer and explanation is:
Correct Answer: a. chemical structure of the R group
Amino acids are the fundamental building blocks of proteins and are essential to many biological processes. Each amino acid shares a common general structure that includes a central carbon atom (called the alpha carbon) bonded to four components: an amino group (-NH₂), a carboxyl group (-COOH), a hydrogen atom, and a variable side chain referred to as the R group.
The chemical structure of the R group is what makes each amino acid unique. While the amino and carboxyl groups are consistent across all standard amino acids, the R group differs in size, shape, polarity, and chemical reactivity. These variations determine the specific properties and functions of each amino acid in a protein.
For example, the R group of glycine is a single hydrogen atom, making it the smallest and most flexible amino acid. In contrast, tryptophan has a large, bulky R group containing a double-ring structure, making it larger and more hydrophobic. Other R groups may carry a charge at physiological pH, such as lysine, which has a positively charged R group, or glutamic acid, which has a negatively charged R group.
These differences influence how amino acids interact with each other in proteins, affecting the folding, shape, and function of the resulting protein. Some R groups are hydrophilic and tend to be found on the exterior of proteins in aqueous environments, while hydrophobic R groups are often buried in the protein’s interior.
In contrast, the size of the amino group, number of carboxyl groups, or number of peptide bonds do not change from one standard amino acid to another. Peptide bonds, for instance, are formed between amino acids during protein synthesis but are not unique to any specific amino acid.
Thus, the R group is the key distinguishing feature.