NOTICE: Citizendium is still being set up on its newer server, treat as a beta for now; please see here for more.
Citizendium - a community developing a quality comprehensive compendium of knowledge, online and free. Click here to join and contribute—free
CZ thanks our previous donors. Donate here. Treasurer's Financial Report -- Thanks to our content contributors. --

Amino acid

From Citizendium, the Citizens' Compendium
(Redirected from Amino acids)
Jump to: navigation, search
This article is developing and not approved.
Main Article
Talk
Related Articles  [?]
Bibliography  [?]
External Links  [?]
Citable Version  [?]
 
This editable Main Article is under development and not meant to be cited; by editing it you can help to improve it towards a future approved, citable version. These unapproved articles are subject to a disclaimer.
(CC) Image: David E. Volk
Amino acid structures.

In biochemistry, an -amino acid is an organic monomer consisting of an amino group, a carboxyl group, a hydrogen atom, and a residual group (commonly denoted as simply "R") covalently bonded to a central (alpha) carbon (C). Amino acids can link via peptide bonds to create short chains (polymers) called polypeptides, often referred to simply as peptides. Longer, more complex chains (or combinations of multiple chains) are called proteins, which have a vast array of biological functions. In peptides and proteins, the R-groups are often called "side chains", because they are not involved in the polymer backbone. Amino acids have two stereo isomers (mirror images of each other), and only the L-isomer is used in protein synthesis.

The Amino Acids

There are twenty common amino acids used by nearly all living organisms as well as several rarer ones. The difference between any two amino acids is the residual (R) group, and they can be categorized based on the chemical properties of the R-groups. Each amino acid has a three-letter abbreviation and a one-letter symbol.

Amino Acids with Non-Polar R-Groups

Amino Acids with Aromatic R-Groups

Amino Acids with Polar, Uncharged R-Groups

Amino Acids with Positively Charged R-Groups

Amino Acids with Negatively Charged R-Groups

Synthesis

Most organisms are unable to synthesize all twenty amino acids. Essential amino acids must be taken in from the environment, whereas nonessential amino acids can be produced by the organism. For humans, there are seven essential amino acids that must be obtained in the diet in order to survive; there are therefore thirteen non-essential amino acids for humans. The number of and the identity of the essential amino acids varies among species.

For humans, the nonessential amino acids can be synthesized in cells through a variety of pathways. For some animals, the amino acid carnitine is essential, but most animals can produce it from lysine.

See Also