Proteins usually have a molecular weight range from 6000 to several million units. They order of arrangement of amino acids in a polypeptide is known as the amino acid sequence. The sequence has some great biological significant. Some chemical and physiological properties arise from the different in the amino acid sequence and also from the nature of folding and bending
- Primary Structure
This is the sequence of amino acids along a polypeptide chain. It is unique for each protein e.g. myoglobin consist of a polypeptide chain of 153 amino acid and an iron containing prosthetic groups.
- Secondary Structure
These refers to the helical coiling or pleating of polypeptide chain e.g. collagen and keratin
- Tertiary Structure (3 dimensional shape)
This refers to the folding or bending of helically coiled chain. These structure is the 3 dimensionnal shape of a polypeptide. The tertiary structure of a protein can be determineif the bonds hiolding the shape are broken. The primary structure is retain but the specific shape is lost. Denatured globular proteins lose their function. The tertiary structure is usually stabilized by several forces such as di-sulphide bond, hydrogen bond, ionic bond and hydrophobic reaction e.g. insulin and myoglobin
- Quaternary Structure
These refers to the association of polypeptide chains, that is the way they are arranged in a protein. E.g. hemoglobin has 4 polypeptide chain and 4 non-protein haem groups.
