Final answer:
Amino acid variation in proteins is influenced by the genetic code, which determines the sequence of amino acids, and the different chemical properties of amino acid side chains.
Step-by-step explanation:
The amino acid variation in proteins is primarily influenced by differences in the genetic code and the nature of amino acid side chains. The genetic code dictates the sequence of amino acids through nucleotide sequences in DNA, which are transcribed into mRNA. Each triplet codon in mRNA specifies an amino acid. A change in the DNA sequence can lead to a change in the mRNA and consequently a different amino acid being incorporated into a protein during translation. This is exemplified by genetic diseases like sickle cell anemia where a single base alteration leads to the substitution of glutamic acid with valine, significantly affecting the protein's function.
Amino acids have 20 common types, each with a unique side chain, or R group, that bestows different chemical and physical properties. These properties influence the protein's overall structure and function, as different side chains will interact differently with each other and the environment, leading to a specific three-dimensional conformation that is essential for protein activity. The variation in side chains is thus a critical factor in the diversity of protein forms and functions.