Primary and Secondary Structure of Protein

1. Primary Structure of Protein

2. Description... Primary structure of protein refers to the sequence of amino acids present in a polypeptide chain. Amino acids are covalently linked by peptide bond. Each component in amino acid in a polypeptide is called “residue”. The different arrangement of amino acids yield different structure with different functions and activities. It determines the shape or conformation, into which a protein can be arranged.

3. Example of Primary Structure Methionine enkephalin Try- Gly - Gly - Phe - Leu Leucine enkephalin Try- Gly - Gly - Phe - Leu

4. Importance of Primary Structure. To predict the 2 nd and 3 rd structure from sequence homologies with related proteins. Many genetic diseases result from abnormal amino acid sequences. To understand the molecular mechanism of action in protein. To trace evolutionary paths.

5. Example of Proteins Insulin – the first protein in which the sequence of amino acids was determined. some insulin from animals is biologically active in humans and can be used for treatment. And insulin from humans, differs slightly by one, two, or three amino residues in chain A.

6. Secondary Structure of Proteins

7. Description... The regular arrangement or coiling of segments of protein chains. A unique three-dimensional shape of each protein which is important to its function. It is the conformation or the shape in a relatively small or localized region of a polypeptide molecule. Secondary structures have repetitive interaction resulting from hydrogen binding between the amide N – H and the carbonyl groups of the peptide backbones.

8. Secondary structure’s consists... α Helix Coiling of the protein chain in the shape of a right-handed helix. e.g α keratin. The C=O oxygen of an amino acid residue is H-bonded to the N-H hydrogen of the 4 th amino acid residing further down the polypeptide chain.

9. α- Helix

10. β pleated sheet – a side by side alignment of adjacent polypeptide chains. H- bonding occurs between C=O oxygen of one chain and the N-H hydrogen of an adjacent. The sheet conformation permits the stacking of sheets one on top of the other.

11. Two Types of β pleated sheet

12. β bends – permits the change in direction of a peptide chain to get a folded structure. - It gives proteins globularity rather than linearity.

13. Triple Helix – right handed super helix by the right-handed coiling of three polypeptide chain. Collagen – most abundant protein in mammals. Constitutes the major portion of tendons and ligaments. Important constituent of skin. Vitamin C is required in the formation of collagen, particularly in the hydroxylation of proline to form hydroxyproline to stabilize the structure of collagen.

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