1. Amino acids and peptides
The “Lego” of proteins

2. Amino Acids Same general structure Called alpha amino acids
L- isomer is physiologically active
Side chain or R group determines other properties
Acid-base properties

3. Amino Acids, General pK of carboxyl group around 2.3
Deprotonated at physiological pH
R – COO-
pK of amino group around 9.5
Protonated at physiological pH
H3N+-R
Some R-groups are acidic or basic

4. Nonpolar amino acids

5. Aromatic Amino Acids

6. Polar Amino Acids, alcohols

7. Polar Amino Acids (sulfur containing)

8. Polar amino acids (amides)

9. Charged Amino Acids (Acidic)

10. Charged Amino Acids (Basic)

11. Titration of Amino acids
Titration of glycine

12. Titration of Glutamate

13. Purification of amino acids
Chromatography
Various types
Ion exchange
Uses net charge or can change with pH
Separate K, D and A
HPLC

14. Electrophoresis
Using electricity to move particles through a gelatinous matrix
Isoelectric point
IEF

15. Peptides Peptide bond is amide linkage between amino acids
No free rotation about C-N bond due to partial double bond character of bond
resonance

16. Tetrapeptide
Note planes of peptide bonds

17. Peptides Peptides are vectorial Sequences read H3N+---COO-
Have N and C termini
Sequences read H3N+---COO-
P-I-G

18. Draw a tetrapeptide of L-A-R-D at physiological pH
Answer

19. Biologically Interesting Peptides
Aspartame
L-aspartyl-Lphenylalanine methyl ester

20. Other small interesting peptides
Enkephalins
Y-G-G-F-L
Y-G-G-F-M
Oxytocin
C-Y-I-Q-N-C-P-L-G-NH2
Has C—C disulfide
Vasopressin
C-Y-F-Q-N-C-P-R-G-NH2
Also disulfide

21. Chemical Synthesis of Peptides
Why?
Done solid phase
Problem with in solution
Hard to make pure desired sequence
Purify by filtration
Side chains blocked
Made backwards ( C---N)

22. Scheme for peptide synthesis

23. Tetrapeptide answer
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