Amino Acids

1. Amino Acids (Chapter 37B)

2. COOH H H2N C R General Structures • Two contrasting groups • -COOH acidic • -NH3 basic • -amino acids • ~20 different -amino acids found in protein in nature 

3. COOH COOH COOH H H H H2N C H2N H2N C C CH3 H CH2COOH 2-Aminopropanoic acid (Alanine) Aminobutanoic acid (Aspartic acid) Aminoethanoic acid (Glycine) Some amino acids

4. eye Chirality COO- • L-amino acid • Look down at H-C bond, other groups, read clockwise (‘corn’ law) C R H3N+ H

5. COO- H +H3N C R Dipolar Ion (Switterion) Special features • High m.p. and b.p. • Glycine (R=H) is a solid • Soluble in water • High dipole moment • Less acidic and basic than normal RCOOH and RNH2

6. COO- COO- + H3O+ H As acid H2N C H +H3N C R As base R COOH + H2O H + OH- +H3N C R Amphoteric

7. COO- COOH COO- H H2N C OH- H+ +H3N H C +H3N H C R OH- H+ R R (II) (I) (III) Isoelectric point pH at which the concentrations of (II) = (III) is called the isoelectric point.

8. Separating amino acids • Chromatography

9. Separating amino acids • Electrophoresis

10. H H H O O N+ C C H H3N+ C C O- O- R H R’ -H2O H H H O Peptide linkage (A Dipeptide) O N C C H3N+ C C O- R R’ Peptide Linkage

11. H H O H O N C C HN C C n R R’ Proteins • Polypeptides • About 20 amino acids • Number of possible protein polymers is very large

12. Proteins