Functions
1. Structural:
collagen: skin, cartilage, bones;
keratin: hair
2. Catalysis: enzymes
3. Movement: muscles
4. Transport: hemoglobin, lipoproteins
5. Hormones: insulin, human growth hormone
6. Protection; antibodies, blood clotting
7. Storage: ferritin stores Fe in liver, egg albumin
8. regulation: control gene expression
Classifications
Fibrous: insoluble proteins used for structural purposes
Globular: soluble in water
Structure
alpha amino acid polymers
Amino end (N-terminus) -NH2
Carboxylic acid end (C-terminus) -COOH
backbone: -N-C-C-N-C-C-N-C-C-N-C-C-N-C-C-
R-Group Classifications
Nonpolar: gly, ala, val, leu, ile, pro, phe, met
Polar
......Neutral: ser, thr, cys, tyr, asn, gln, trp
......Acidic: asp, glu
......Basic: lys, arg, his
Zwitterion ("hybrid ion") can either accept or donate H+ depending upon the pH
Cationic..... low pH
Neutral..... isoelectric point
Anionic.....high pH
Electrophoresis- separation based on charge
Levels of structure
Primary: amino acid sequence
Secondary: folding or coiling due to backbone interactions (hydrogen bonding)
1) alpha helix
2) beta pleated sheet
3) triple helix: collagen
Tertiary: overall shape determined by R-group interactions
1) salt bridge: ionic
2) hydrogen bonding
3) disulfide bond: covalent S-S bond
4) hydrophobic interactions
Quaternary: interaction between two or more proteins
......conjugated protein: protein plus non-protein prosthetic group
Denaturation
1) pH Heavy metal ions:Ag+, Pb2+, Cd2+, Hg2+
2) Heat Mechanical agitation
3) Solvents Radiation
