|3.4 HaemoglobinHaemoglobin is the famous oxygen-carrying, globular protein, found in the red blood cells.
- It is made up of four polypeptide chains, and each chain itself is known as globin. There are many types of globin – two of which are used to make haemoglobin, and two which are Alpha-globin and Beta-globin.
- The haemoglobin molec. is nearly spherical.
- The interactions between the R groups inside the molec. are important in holding it in its correct 3D shape. The out-ward pointing hydrophilic R groups are important in maintaining its solubility.
- Each polypeptide chain of haemoglobin contains a haem group. A group like this which is an important part of a protein molec. but is not made of amino acids is called a prosthetic group.
- Each haem group contains an iron atom, where O2 molecules can bind. A complete haemoglobin molecule with four haem groups can carry for oxygen molecules.
- Haem groups are also responsible for the colour of the blood. As the colour changes from purplish (low concentration of O2) to bright red (high concentration of O2) the haemoglobin becomes oxygenated.This is known as oxyhaemoglobin.
Sickle Cell Anaemia
– In this genetically inherited condition, one amino acid which occurs in the surface of the B-chain is replaced with a different amino acid. The correct one is glutamic acid, which is polar. The substitute is valine, which is non polar. This substitution makes haemoglobin much less soluble, and causes unpleasant and dangerous symptoms.