Amino acids

Amino acids are the building blocks of proteins. There are 20 naturally occurring amino acids. (1) Amino acids exist in proteins as L-optical isomers, however they can extist as D-isomers in isolated examples. E.g. some bacterial cell walls contain D-isomers.

Amino acids can also be characterized as polar or non-polar, these dictate the amino acid function. There are 10 non-polar amino acids, these are found in protein core. There are also 10 polar amino acids, these have enzymatic roles, they can be used to bind DNA, metals and other naturally occuring ligands. There are essential amino acids and non-essential amino acids. Essential amino acids are the ones that the body cannot synthesise on its own. These amino acids have to be supplied to the body via digested proteins. The digestion of cellular proteins is also an important source for amino acids. Non-essential amino acids can be synthesised from compounds already existing in the body.

Amino acids have been abbreviated into a 3 letter code as well as a 1 letter code. For example, Glycine has the 3 letter code 'Gly' and is assigned the letter 'G' (see single letter amino acid codes).

List of Amino acids, their charges and side chain polarity:

Alanine  (A) Charge = 'Polarity = nonpolar

Cysteine (C) Charge =neutral.Polarity = nonpolar

Aspartic Acid (D) Charge =negative.Polarity = polar

Glutamic Acid (E) Charge = negative. Polarity = polar

Phenylalanine (F) Charge = neutral. Polarity = nonpolar

Glycine (G) Charge = neutral. Polarity = nonpolar

Histidine (H) Charge = neutral. Polarity = polar

Isoleucine (I) Charge = neutral. Polarity = nonpolar

Lysine (K) Charge = positive. Polarity = polar

Leucine (L) Charge = neutral. Polarity = nonpolar

Methionine (M) Charge'= neutral.P'olarity = nonpolar

Asparagine (N) Charge = neutral. Polarity = polar

Proline (P) Charge = neutral. Polarity = nonpolar

Glutamine (Q) Charge = neutral. Polarity = polar

Arginine (R) Charge = positive. Polarity = polar

Serine (S) Charge = neutral. Polarity = nonpolar

Threonine (T) Charge = neutral. Polarity = polar

Valine (V) Charge = neutral. Polarity = nonpolar

Tryptophan (W) Charge = neutral. Polarity = nonpolar

Tyrosine (Y) Charge = neutral. Polarity = polar

Amino acid structure

All amino acids have a carboxyl terminus, and an amino terminus, but they differ in their residual groups. Amino acids are bonded together by a covalent linkage called a peptide bond . Amino acids contain both a carboxyl group (COOH) and an amino group (NH₂).