In: Biology
Amino acids are the building blocks of proteins.
The name “amino acid” is derived from the fact that they contain both amino group and carboxyl-acid-group in their basic structure.
There are 20 different amino acids in nature. All amino acids include five basic parts:
The R-group (side chain) is what makes each amino acid unique. Sidechains contain mainly hydrogen, carbon, and oxygen atoms. Some amino acids have sulfur or nitrogen atoms in their R-groups. The chemical nature of the side chain determines the nature of the amino acid (ie, whether it is acidic, basic, polar, or nonpolar).
The sequence and the number of amino acids ultimately determine the protein’s shape, size, and function. Each amino acid is attached to another amino acid by a covalent bond, known as a peptide bond, which is formed by a dehydration reaction.
The products formed by such linkages are called peptides. As more amino acids join to this growing chain, the resulting chain is known as a polypeptide.
Each polypeptide has a free amino group at one end. This end is called the N terminal, or the amino-terminal, and the other end has a free carboxyl group, also known as the C or carboxyl-terminal.
While the terms polypeptide and protein are sometimes used interchangeably, a polypeptide is technically a polymer of amino acids, whereas the term protein is used for a polypeptide or polypeptides that have combined together, often have bound non-peptide prosthetic groups, have a distinct shape and have a unique function.
After protein synthesis (translation), most proteins are modified. These are known as post-translational modifications. They may undergo cleavage, phosphorylation, or may require the addition of other chemical groups. Only after these modifications is the protein completely functional.