Amino Acids

Here is a summary of key facts about amino acids with links to more about individual amino acids.

What are Amino Acids ?

There are over 20 amino acids. Although they differ from each other, all amino acids have similar basic structures and similar or related functions within the body.

Two categories (groups) of Amino Acids:

There are two types of amino acid:

  • Those that can be synthesized by the body itself, and
  • Those that, while necessary for healthy growth or maintenance of the body, cannot be produced by the body itself.

The second type of amino acids are called 'Essential Amino Acids', and are also referred to as 'Indispensible Amino Acids' in some textbooks. Conversely, those that can be produced within the body itself (generally from an excess of certain other amino acids in the body) are referred to as 'Non-Essential' or 'Dispensible' amino acids because, although their presence in the right quantity is important for good health, they are not essential within a person's diet.

Which amino acids are in each category ?

The Structure / Chemistry of Amino Acids

(1) What do they have in common ?

All amino acid molecules include the following in their chemical structures:

In chemistry, a carboxyl group is a functional group consisting of a carbon atom double-bonded to an oxygen atom and single-bonded to a hydroxyl (-OH) group, as indicated by the structure drawn on the right.

Carboxyl groups are weakly acidic and are the characteristic constituents of carboxylic acids. They are present in most organic acids, and are biodegradable.

Amino means there is an -NH2 group.

When amino groups occur in organic substances (such as amino acids), they are generally attached to a carbon atom.


Long strings, or 'chains' of thousands of the 20 amino acids that form proteins linking together form the proteins that exist in the body. These chains generally consist of repeated sequences of specific amino acids.

(2) How do the amino acids differ from each other ?

It is the SIDE GROUPS which make each amino acid different from the others.

Of the 20 amino acids used to make proteins, there are three groups.

These three groups are:

  • Ionic
  • Polar, and
  • Non-polar.

These names refer to the way the side groups (sometimes called 'R' groups) interact with the environment. Polar amino acids have a tendency to adjust themselves in a certain direction. Non-polar amino acids don't really care what's going on around them. Ions are atoms (or, more accurately, parts of atoms) that are charged because they have either gained or lost negatively charged electrons. It is this difference in the charge on ions that holds ionic substances together.

Biology Textbooks

Systems Biology Veterinary Science Textbook

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