Proteins 2

Table of Contents
Biomolecules Gateway Page
Jmol Tutorial

In this module:

Secondary Structure
α Helices
ß Sheets
Tertiary Structure
Disulfide Bonds, Domains
Cofactors, Quaternary Structure
Protein Folding
Alzheimer's and "Mad-Cow" Diseases

Disulfide Bonds

One important determinant of tertiary structure in some proteins is the disulfide bond . Cysteine residues in different parts of the protein can be linked by the oxidation of their sulfur atoms. For example, insulin (right), a molecule which directs the uptake of glucose from the bloodstream by cells in the pancreas, consists of two short protein chains (blue and green) linked by three disulfide bonds (yellow).


Many proteins are composed of two or more relatively independent structures or domains linked by flexible and unstructured protein sequences. For example, antibodies (right) have two identical recognition domains linked to a constant region that sends a signal to cells in the immune system. Membrane receptor molecules have a binding domain on one side of the membrane linked to a signal domain on the other side of the membrane that carries on the signal inside the cell.

Disulfide Bonds and Domains