Chemistry of proteins, primary structure, secondary structure,alpha-helical structure , beta-pleated sheet,parallel pleated sheet, anti-parallel sheet, tertiary structure, Quaternary structure

chemistry of proteins, primary structure, secondary structure,alpha-helical structure , beta-pleated sheet,parallel pleated sheet, anti-parallel sheet, tertiary structure, Quaternary structure

1. BIOCHEMISTRY & CLINICAL PATHOLOGY TOPIC- CHEMISTRY OF PROTEINS PRESENTED BY- SHWETA MISHRA

2. CHEMISTRY OF PROTEINS The structure of protein can be classified as follows: Primary structure Secondary structure Tertiary structure Quaternary structure PRIMARY STRUCTURE The primary structure of the proteins mainly refers to the number of amino acids, their nature and their sequence. The change in the sequence of amino acids can change their physiological effects. Primary structure refers to the sequence of amino acids which are linked through peptide bonds. The peptide bond occurs between the carboxyl group(-COOH) of one amino acids and amino group of(-NH 2 ) of another amino acids. H 2 N-CH 2 -COOH + H 2 N-CH 2 -COOH H 2 N-CH 2 - CONH -CH 2 -COOH + H 2 O Glycine Glycine Peptide bond

3. SECONDARY STRUCTURE The secondary structure refers to the shape of the peptide chain indicating whether the polypeptide chain is linear, cyclic, branched OR arranged in the form of helix. The secondary structure exists in the following two different forms. Alpha(α) helical structure- An 𝞪-helical conformation was proposed in 1950 by Linus Pauling & Robert Corey . This structure is formed by the twists of the polypeptide chain like a right handed screw. This results from the coiling of the protein such that peptide bonds making up the backbone of protein form the hydrogen bonds between each other. The hydrogen bonds are directed along the axis of the helix. 𝞪- helices have 3.6 amino acids residues per turn, i.e. a helix 36 amino acids long would form 10 turns. The protein keratin of skin, hair and nail is rich in alpha-helical structure.

4. Fig. showing alpha helical structure of protein

5. Beta(𝜷) pleated sheet- The beta-pleated sheet(also called beta sheet) is the second form of regular secondary structure in proteins. It is less common than the alpha-helix. The beta-pleated structure of polypeptide have extended polypeptide chain and hydrogen bond present between polypeptide strands run antiparallel to each other. In 𝜷 conformation, the backbone of the polypeptide chain is extended into a zigzag. The zigzag polypeptide chain can be arranged side by side to form a structure resembling a series of pleats. In this structure the polypeptide chain arranges in two types- Parallel pleated sheet Anti-parallel pleated sheet

6. Fig. showing alpha helical structure of protein

7. Fig. showing parallel and antiparallel beta pleated sheet

8. TERTI ARY STRUCTURE The tertiary structure mainly refers to the forces that hold the peptide chains together and arrangement of individual peptide chains in definite manner. In this structure the chain folds, forms loops and gives 3-D shape. This structure represents the folding of a protein that controls the basic functioning of the protein. If this is disrupted, it loses its activity. The long polypeptide chains are tightly folded into a compact form due to the following interactions- Hydrogen bonding Disulphide bonding Ionic bonding Hydrophobic bonding

9. QUATERN ARY STRUCTURE All proteins have 1°, 2 °, 3° structure but not all proteins have quaternary structure. Quaternary structure is the arrangement of subunits that form a large proteins. The quaternary structure refers to the number of peptide chains and their arrangement in the natural protein molecule. This structure forms when two or more polypeptide chains interact with each other and form a large assembly or complex of a protein.

10. Fig. showing quaternary structure of protein

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