Amino Acids
I.
BASIC STRUCTURE
A. All amino acids have an  carbon that forms four bonds
1. Amino group
2. Carboxyl group
3. A hydrogen atom
4. One of 20 side chains
II.TYPES
A. There are 20 common amino acids
1. These vary in their side chain
B. Amino acids can be classified according to its side chain characteristics
1. Hydrophobic aliphatic
2. Hydrophilic aliphatic
3. Hydrophobic aromatic
4. Hydrophilic aromatic
5. Sulfur containing
a) Theses include cysteine and methionine
b) Cysteine is capable of forming a disulfide bond with and second cysteine
(1) Disulfide bonds are the only common covalent bond between amino acid side
chains
6. Cationic
7. Anionic
C. Essential amino acids
1. Humans can make 11 amino acids from carbohydrates and nitrogen
2. The other amino acids are not made by humans and must be ingested
a) These are termed the essential amino acids
b) These are mostly the amino acids with hydrophobic side chains
III.SYNTHESIS
A. Nitrogen must be incorporated into the an organic molecule
1. Ammonia is added to -ketoglutarate to form glutamate
a) This is referred to as reductive amination as it requires the expenditure of a
NADPH molecule
2. The glutamate donates the amine group to other organic molecules to form the
various amino acids
a) This reaction is catalyzed by transaminases
b) The amine group of -ketoglutarate is traded for the oxygen atoms on
various organic molecules
3. Alternatively, glutamate can be transformed into other amino acids
IV.ENERGIZATION
AND LINKAGE OF AMINO ACIDS
A. Energization
1. Amino acid + ATP  Amino acid - AMP + pyrophosphate
B. Linkage
1. Amino acids are linked to appropriate tRNA molecules
a) This reaction is catalyzed by various amino-acyl tRNA synthetases