Summary of Amino Acids

Amino Acids
GENERAL...................................................................................................................................................... 2
PROPERTIES OF AMINO ACIDS:....................................................................................................................................2
PEPTIDE BONDS:.......................................................................................................................................................2
NON-POLAR.................................................................................................................................................. 3
POLAR UNCHARGED...................................................................................................................................... 4
POLAR CHARGED ACIDIC............................................................................................................................... 4
POLAR CHARGED BASIC................................................................................................................................. 5
AMINO ACID MODIFICATION (POST-TRANSLATION)......................................................................................5
AMINO ACID SIDE CHAIN REACTIONS............................................................................................................ 5
STEREOCHEMISTRY OF AMINO ACIDS............................................................................................................ 6
OPTICAL ACTIVITY: ABILITY TO ROTATE THE PLANE OF POLARIZED LIGHT..............................................................................6
D/L NOMENCLATURE: DIFFERENT TO THE ABOVE...........................................................................................................6
R/S NOMENCLATURE:...............................................................................................................................................6
ACID-BASE PROPERTIES OF AMINO ACIDS..................................................................................................... 7
AMINO ACIDS ARE POLYPROTIC ACIDS:.........................................................................................................................7
PKA:.......................................................................................................................................................................7

CHROMATOGRAPHY..................................................................................................................................... 8
PAPER CHROMATOGRAPHY:.......................................................................................................................................8
LIQUID CHROMATOGRAPHY:.......................................................................................................................................8




1

, Amino Acids
General
Carbon is the most important element of life.
Catenation: The ability of a chem element to form long chain-like structures via a series of
covalent bonds

Properties of amino acids:
- Tetrahedral C atom with 4 different chem group covalently attached:
o NH2 – Amino group
o H – Hydrogen
o COOH – Carboxyl group
o R – Side chain
- In the absence of a side chain, amino acids exist at neutral pH as zwitterions.
- Cationic form: net charge = +1 (low pH)
- Zwitterion : net charge = 0 (neutral pH) (Isoelectric point (pI))
- Anionic form: net charge =-1 (high pH)

pI’s can be calculated from pKa’s of functional groups of amino acids

Peptide bonds:
- Formed when alpha-Carboxyl and alpha-amino groups of 2 amino acid molecules
react, releasing 1 mol of water through condensation.

20 common amino acids in proteins bearing different side chains.




2