The Secondary Structure has 2 parts to it. The primary structures polypeptide chain can do two things; 1) it can twist round to form an Alpha- Helix, this looks like a spiral. In this helix Hydrogen bonds form between the C=O of the carboxylic acid and the –NH of the amine group of different amino acids, this stabilises the shape in its form. Many chains may join together with hydrogen bonds holding the parallel chains together; this is known as a Beta-Pleated sheet.
Inside 1 molecule there could be sections with Alpha-Helices and other sections that include Beta-Pleated sheets. The Beta-Pleated sheets attract water and means they are polar, this means when they have the chance they will form hydrogen bonds with surrounding water. They are also charged, ‘an example of an Amino Acid with these characteristics is Glutamate.’ (, 12th Oct). Alpha-Helix amino acids are the opposite of Beta-Pleated ones, Alpha-Helices are water repelling and turn inwards away from water, they are also uncharged, and ‘an example of an Alpha-Helix Amino Acid is Serine.’ (, 12th Oct)
The Tertiary Structure of a protein is often when it is bent and folded to produce an exact 3D shape. These are held in place by Chemical Bonds and Hydrophobic interactions between R groups however, these are often weak interactions. ‘Ionic Bonds between a positively charged and negatively charged amino acid side-chain group are also involved in stabilizing the tertiary structure.’ (, 12th Oct).
The Quaternary Structure, Proteins are often made up of more than 1 folded protein unit that is joined together. Haemoglobin is an example of a quaternary structured protein; it is found in red blood cells and carries oxygen around in the blood stream, (it also makes the blood red) it is made up of 4 polypeptide chains held tightly together. These can also be held in place with the same bonds and interactions as in a tertiary structure. Ionic Bonds join Hydrophilic and Hydrophobic side chains, Hydrogen Bonds join together only Hydrophilic side chains and a Disulphide Bond join only Hydrophobic side chains.
Controlling the shape of the protein depends on what is in the polypeptide chain, the genetic information stored in the D.N.A. Some proteins are continuously produced in a cell such as Cystic Fibrosis Transmembrane Regulator will become channel proteins in the membrane. The protein channel facilitates the proteins through.
To conclude, all of the Hormones, Antibodies and Enzymes (which are all proteins) that we need in our body are all made of 4 different structures Primary, Secondary, Tertiary and Quaternary. These all get bigger by different lengths and inclusions of amino acids in the polypeptide chains. The shape and overall structure though is what defines each structure is correct for each protein.
BIBLIOGRAPHY
- Salters-Nuffield Advanced Biology
- Class Notes
