Proteins

• Contains hydrogen, carbon, oxygen, and NITROGEN
• Possibly contains sulphur or phosphorous 

Built up of sub units called amino acids

Amino acids contain an amino group, a carboxyl group and an R group

The amino group of one amino acid reacts with carboxyl group of another in a condensation reaction

A dipeptide is formed

1) Primary

Sequence of amino acids in a polypeptide chain

2) Secondary

First level of protein folding

Forms an alpha helix or a beta pleated sheet

3) Tertiary

Proteins in secondary structure can be folded to give a complex, compact 3D shape

Maintained by hydrogen bonds, ionic bonds, disulphide bridges and hydrophobic interaction

4) Quaternary

Two or more polypeptide chains in tertiary form combined

Can contain a prosthetic group e.g. haemoglobin

Fibrous

e.g. keratin, collagen

3 alpha helices combined

Insoluble, strong and tough

Globular

e.g. antibodies, enzymes, hormones etc.

Compact and soluble

Haemoglobin is 4 pp chains, with an prosthetic group - haem

Biuret

• Add biuret reagent to solution
• If protein present -> purple
• If protein is not present -> remains blue