Secondary Structure

The primary structure can fold into several simple repetitive patterns which are held together by hydrogen bonds. The main two patterns are alpha-helix and beta-sheet.

beta-sheet (Dotted lines are hydrogen bonds. Thick lines are the polypeptide backbone.)

alpha-helix

By hydrogen bonding, the polypeptide chain forms units of structure such as alpha-helix and beta-sheet. Hydrophobic interactions result in non-polar amino acids being buried in the centre of the protein molecule. Covalent bonding between the sidechains of cysteine forms disulphide bridges which tie the molecule together (this is usually seen in secreted proteins, which need extra stability).

Primary structure & introduction

Tertiary structure

Quaternary structure & summary