Unit 2.1 Topic 6

Amino acids - the monomers of proteins.

Proteins in living organisms.

Proteins make up about 50% of the organic matter of a cell. They are large molecules, made up of the elements carbon, hydrogen, oxygen and nitrogen. Some proteins also contain sulphur.

Proteins have many functions:

• they are structural components, e.g. of muscle and bone.
• they are membrane carriers and pores, e.g. for active transport and facilitated diffusion.
• all enzymes are proteins.
• many hormones are proteins.
• antibodies are proteins.

All proteins are made from amino acids.

Proteins are large molecules because they are polymers. They are made by joining together a large number of similar, smaller subunits (monomers). The monomers that are joined together to make proteins are called amino acids. A protein consist of a long chain of amino acids joined end-to-end.

Amino acids - similar but very different.

All amino acids have the same basic structure. They all have an amino acid group at one end of the molecule, an acid group at the other end of the molecule, and a carbon in between.

Amino acids joined end-to-end giving a repeating 'backbone'. For example, joining four amino acids together would give a backbone N-C-C-N-C-C-N-C-C-N-C-C.

Not all amino acids are identical. There are 20 types of naturally occurring amino acid. Each one is based on the same structure as shown above, but there are differences between amino acids because they have different R-groups.

The R-group in glycine…