Primary and secondary structural organization of proteins Commissionerate

Primary and secondary structural organization of proteins Commissionerate of Collegiate Education

• The four important biomolecules carbohydrates, proteins, lipids and nucleic acids. • Most abundant • 50 % dry weight of cell Commissionerate of Collegiate Education

• All proteins are made of only 20 types of amino acids. • A protein molecule is a polymer of amino acids. • Before we study the structure of proteins let us study the structure of amino acid. Commissionerate of Collegiate Education

General structure of amino acid • In the middle of the amino acid molecule a central carbon atom • It is called α carbon atom. • An acidic carboxyl – COOH and, a basic – NH 2 group • As well as a H atom are attached to the α carbon atom. Commissionerate of Collegiate Education

• Only the 4 th position changes among the amino acids. • It is called the “R” group. • It is this group that gives specificity to an amino acid. Commissionerate of Collegiate Education

Formation of a protein molecule • Carboxyl group of an amino acid reacts with amino group of next amino acid. • A molecule of H 2 O is released - condensation - two amino acids are bonded by a peptide bond. • Amino acid residues. Amino acids are serially ; polypeptide bonded, folded - a protein. Commissionerate of Collegiate Education

• 4 levels of structural organization • • 1 Primary structure 2 Secondary structure 3 Tertiary structure and 4 Quaternary structure Commissionerate of Collegiate Education

• 1 Primary structure • Exact sequence of amino acids • Lysozyme; 129 residues seuence is primary structure of lysozyme • 4 disulphide bonds. • Free amino group on left side, free carboxl group on right side. Commissionerate of Collegiate Education

• Insulin; A chain-21 residues • B chain 30 residues; sequence of A chain, B chain primary strucrure of insulin. 2 disulphide bonds. • Human body- thousands of types • Substitution of even one amino acid-serious consequences. Commissionerate of Collegiate Education

2. Secondary sturcture • 3 dimensional form of all sections of back bone. Two forms • 1. α helix and 2. β pleated sheet. • α helix; common, pulled spiral spring; maintained by H bonds between adjacent CO and NH groups; 1 st to 5 th : 3. 6 ; keratin Commissionerate of Collegiate Education

• β pleated sheet; less common • Fibroin-many polypeptide chains; parallel; same direction or antiparallel • C=O and NH groups, and NH and C=O groups of adjacent polypeptide chain joined by H bonds • All C=O and NH groups H bonded, strong, stable. Commissionerate of Collegiate Education