Proteins are important in all biological processes.
Virtually all catalysts that are biological proteins are called enzymes.
Proteins intercede a large range of functions, including transport, storage, coordinated motions, mechanical support, immune protection, excitability, integration of metabolism, and the control of growth.
The core backbone of proteins are called amino acids, and all organic life form are constructed from the basic set of twenty amino acids. The categorizing of these amino acids are as follows:
Aliphatic side chains - correspond to glycine, alanine, valine, leucine, isoleucine, and proline.
Hydroxyl aliphatic side chains - correspond to serine and threonine.
Aromatic side chains - correspond to phenylalanine, tyrosine, and tryptophan.
The basic side chains - correspond to arginine, lysine, histidine.
Acidic side chains - correspond to aspartic acid, glutamic acid.
Amide side chains - correspond to asparagine and glutamine.
Sulfur side chains - cysteine, and methionine.
Amino acids are joined together by peptide bonds to form polypeptide chains.
Peptide bond formation joins a carboxyl group of one amino acid and an amino group of another amino acid. Disulfide bond are formed by cysteine residues.
A specific biological protein is determined by its conformation, i.e. the three dimensional molecular arrangement.
The repeated units of a polypeptide chains are alpha helices, ß pleated sheets, which are formed by folding of the short polypeptide segments in the protein.
Proteins are stabilized by strong hydrogen, van der Waals, and hydrophobic interactions.
Proteins can recognize and interact with a large variety of molecules, they can fold into unique structures and form complementary domains or surfaces, and clefts.
An enzymes controlling catalytic ability comes from its capability to bind substrates in precise orientations, and to stabilize transition states by bond breaking and formation.
Proteins are able to transcend energy and information between distant sites of the molecule by transmission of conformational changes.