• 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


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Formation of Peptide Bond

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

A dipeptide is formed


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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

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Globular and Fibrous


e.g. keratin, collagen

3 alpha helices combined

Insoluble, strong and tough


e.g. antibodies, enzymes, hormones etc.

Compact and soluble

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

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Test for Protein


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