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