Unit+1

=Biological Molecules=

__Topic C:- Proteins__
11) The primary structure of protiens is simply the linear arrangement of amino acids in a straight chain.

Secondary structure is caused by hydrogen bonding between amino acids in the polypeptide. There are two types of secondary structure; Alpha helix's and Beta pleated sheets. The Tertiary Structure is the compact globular structure formed by the folding up of a whole polypeptide chain. Every protein has a unique tertiary structure, which is responsible for its properties and function. For example the shape of the active site in an enzyme is due to its tertiary structure. The tertiary structure is held together by bonds between the R groups of the amino acids in the protein.

There are three kinds of bonds involved: 1) __hydrogen bonds__, which are weak. 2) __ionic bonds__ between R-groups with positive or negative charges, which are quite strong. 3) __Di-sulphide bridges__ - covalent S-S bonds.



The Quaternary Structure is found in proteins containing more than one polypeptide chain, and simply means how the different polypeptide chains are arranged together. The individual polypeptide chains are usually globular e.g.: __Haemoglobin__, the oxygen-carrying protein in red blood cells, consists of four globular subunits arranged in a tetrahedral (pyramid) structure. Each subunit contains one iron atom and can bind one molecule of oxygen.

The Quaternary structure of Haemoglobin

12) All amino acids contain four distinct chemical groups connected to a central carbon atom:
 * a single hydrogen atom ||
 * an amino group (NH2) ||
 * a carboxyl group (COOH) ||
 * a side chain (This side chain, represented by the letter R, differs in different amino acids)

[|13) To see the process of condensation press here]