Proteins have defined three-dimensional structure. There are a number of factors which determine the exact shape of a protein. These are a number of factors which determine the exact shape of a protein. There are consider in terms of four levels of structural organisation called the primary, secondery, tertiary, and quaternary strictures of the protein.
Each succeeding level organisation is more complex than the previous one and is a direct result of the chimecal features of the previous levels.
- Primary Structure- The structure of proteins refers to the sequence of amino acids held together by peptide linkage. The amino acids sequence in proteins can be determined by the methods have been applied to a number of the primary and several generalisation regarding made. They are: (a) Proteins are made up of L-amino acids only; (b) A proteins may contain more than one amino acids along acids chain. If so, the chains are usually bonded to each other at specific points by disulphide-S-S- linkage; chain is essentially random. Repeating sequence of amino have pronounced effect on the chemical and physical properties of proteins.
2. Secondery Structure - The secondary structure of proteins refers to the shape in proteins consists of amino acid chain coiled into be either right- or in the case of screws. The right- handed helix is known as the the bita- helix. It has been found that an alfa- helix spiral is held together by hydrogen bonds bet- cent to one another in the helix approximately 3.6 amino acid units for each turn in the helix.
3. Tertiary Structure- An alfa- helix may be considered to be a piece of a rope which is free to bend, twist, and fold. The tertiary structure of a protein refers to the final three-;dimensional shape that results from the twisting bending, and folding of the protein helix.
4. Quaternary Structure- Complex proteins are often formed from two or more amino acid chain rather than a single amino acid chain. Each chain is a complete proteins with characteristics primary, secondary, and tertiary structure.
The quaternary Structure- refers to the way in which these amino acids chains of a complex proteins are associated with each other.
