D’YOUVILLE COLLEGE BIOLOGY 102 - INTRODUCTORY BIOLOGY II LECTURE # 6 ORGANIC CHEMISTRY IV 6. Proteins: • major structural and regulatory molecules of living systems, e.g. myosin, hemoglobin, insulin, growth hormone, antibodies, enzymes (fig. 5 - 15 & ppt. 1) • polymers of amino acids: - -amino acid -- basic structural formula (ppt. 2): H | H2N-C-C=O | | R OH - groups according to side chain properties: 20 amino acids commonly occurring in proteins fall into groups depending on the properties of the side-chain (R): hydrophobic (non-polar), hydrophilic (polar, positive ionic – basic and negative ionic – acidic) (fig. 5 – 16 & ppts. 3 – 5) - peptide bonding: (linkage between basic amino and acidic carboxyl groups); another example of dehydration synthesis (fig. 5 – 17 & ppt. 6) • protein structure: (fig. 5 – 20 & summary ppt. 12) - structure determines shape; shape determines function (figs. 5 – 18, 5 – 19 & ppt. 7) - primary: amino acid sequence from N terminus (amino) to C terminus (carboxyl); backbone consists of carbonyl, carbon & amino (fig. 5 – 20 & ppt. 8) - secondary: pattern of coiling of peptide chain (helix) or sheet-like organization ( pleated sheet); stabilized by H–bonding between neighboring peptide bonds (fig. 5 – 20 & ppt. 9) - tertiary: pattern of folding into globular proteins or twisting into fibers (fibrous proteins); stabilized by interactions of side-chain (R) groups (H – bonds = polar group interactions, ionic bonds, hydrophobic interactions & covalent bonds = disulfide bridges) (fig. 5 – 20 & ppt.10) - quaternary: details of subunit structure (multiple polypeptides), e.g. hemoglobin (fig. 5 – 20 & ppt. 11); even minor modifications that affect shape can profoundly alter function (fig. 5 – 21) - folding process of new polypeptide facilitated by chaperone proteins (fig. 5 – 24) - denaturation: loss of conformation (secondary & tertiary structure) through heating, extremes of pH; (disruption of H-bonds, ionic bonds & hydrophobic interactions) (5 – 22 & ppt. 13) - conjugated proteins: contain components other than amino acids