protein structure

The job of a protein is completely determined by the structure of the protein, from the smallest to the largest part. There are several ordered layers to the structure

1. The primary structure
The primary structure is the sequence of amino acids found in the polypeptide chain. Amino acids are joined together by peptide bonds which are formed in a condensation reaction.

There are three main components to an amino acid:

a. Carboxyl group: COOH
b. Amine group: NH2
c. Residual group: R

It is the residual group that determines the character of the amino acid, and in turn the structure and function of the whole protein!

2. Secondary Structure
There are two forms of secondary structure

a. Alpha Helix: Where the chain twists up to form a spring like structure. Hydrogen bonds forming between the C=O of the carboxyl group and the -NH of the amine group.

b. Beta pleated sheets: Several chains link together with hydrogen bonds to form a pleated motif.

Both of these structures can occur in one protein.

3. Teritary and Quarternary structure
When the chain bends into a three dimensional shape it is reinforced by chemical bonds between the R groups.

Some proteins can be made up of more than one polypeptide chain and this is the quaternary structure. For example, haemoglobin is made up of four polypeptides.

Globular proteins vs. Fibrous proteins Textbook page 59

Links:
SNAB tutorial note: you may need to log in before folowing this link
Unilever tutorial
Protein Data Bank

Extension:
Medical Research Council CF tutorial

Activity:
Revision Worksheet Available Until 24th October 2007