Glossary · Sinh học
Amino acid
The monomer that builds proteins. Each amino acid has a central carbon bonded to an amino group, a carboxyl group, a hydrogen atom, and its own R group (side chain) — and the chemical nature of that side chain determines the amino acid's nature.
Every amino acid shares the same fundamental structure: a central carbon, the alpha carbon, bonded to an amino group, a carboxyl group and a hydrogen atom.
What differs is the other atom or group of atoms bonded to that carbon, known as the R group. The chemical nature of this side chain determines whether the amino acid is acidic, basic, polar or nonpolar: valine, methionine and alanine are nonpolar or hydrophobic, while serine, threonine and cysteine are polar with hydrophilic side chains.
According to OpenStax, it is primarily the interactions among R groups that create a protein's complex three-dimensional tertiary structure: when folding takes place, the hydrophobic R groups lie in the protein's interior while the hydrophilic R groups lie on the outside. The sequence of amino acids in a polypeptide chain, meanwhile, is the protein's primary structure, and that sequence is specified by DNA.