1 Amino acid and proteins Ghollam-Reza Moshtaghi-Kashanian Biochemistry Department Medical School Kerman University of Medical sciences

2 Classification of Bio-Molecules Proteins Wide range of roles Within the cell Enzymes Structural Gene activators / suppressors Membrane receptors / transporters Contractile elements

3 Proteins Wide range of roles Outside of the cell Enzymes Structural Hormones Antibodies Toxins Transporters (Membrane receptors / transporters)

4 Proteins How do they accomplish so many functions? A multitude of shapes Interact selectively with other molecules High specificity

5 Proteins Structure Polymers of amino acid (  ) monomers Two aspects of  structure Shared properties Properties unique to each 

6 Proteins Amino Acids – Shared properties A carboxyl and an amino group separated by a carbon atom – the  carbon. At physiological pH the  carboxyl looses a proton and the amino group accepts a proton

7 Proteins Amino Acids – Shared properties During protein synthesis each amino acid is linked to the next via a peptide bond – forming a polypeptide A peptide bond results from the linkage of the carboxyl group of one amino acid to the amine group of its neighbor, with the elimination of a molecule of water

8 Proteins Amino Acids – Unique properties The side chain group or R group – 20 forms R group properties provide the basis of the diverse structure and activities of proteins.

9 Amino Acids – Unique properties The side chain group or R group – 20 forms

10 Amino Acids – Unique properties The side chain group or R group – 20 forms

11 Proteins Structure Description at several levels of organization Primary, secondary, tertiary, quaternary

12 Proteins Structure Primary  sequence Possible variations x = 20 n, where n = the no.  in the polypeptide If n = 10 X = If n = 20 X = 10 26

13 Proteins Structure Secondary Conformation of specific regions Two specific types Alpha helix Beta-pleated sheet – composed of  strands Portions not organized into an  helix or a  sheet consist of turns, hinges, loops or finger-like extensions

14 Proteins Structure Secondary In pictorial representations  helices are shown as helical ribbons and  strands as flattened arrows

15 Proteins Structure Tertiary The conformation of the entire protein Ribonuclease Leptin

16 Proteins Structure Quaternary Multiples of single polypeptides linked together Each polypeptide is termed a subunit May be linked by Covalent disulfide bridges Non-covalent between hydrophobic patches In two-polypeptide proteins: if the subunits are identical – it is a homodimer If the subunits are different – it is a heterodimer

17 Proteins Structure Dynamic changes within proteins Protein structure is not rigid or inflexible Capable of considerable internal movements Some random and small-scale Predictable changes triggered by interaction with another molecule are conformational changes Complexes of proteins form and break Association and Dissociation Interacting proteins have complementary surfaces As they come into close contact their interaction is stabilized by non-covalent bonds