ORGANIC CHEMISTRY 3540

AMINO ACIDS

STRUCTURE

PROPERTIES

A PROTEIN

AN AMINO ACID

PROTEINS ARE POLYMERS OF AMINO ACIDS

~200 AMINO ACIDS FOUND IN LIVING CELLS

~20 AMINO ACIDS IN MOST PROTEINS

ESSENTIAL AMINO ACIDS
• NEEDED BY ORGANISM BUT THE ORGANISM CAN'T SYNTHESIZE IT
• MUST BE IN DIET!

FOUR TYPES (CLASSIFIED BY SIDE CHAIN)

1. NONPOLAR SIDE CHAINS (HYDROPHOBIC)
LEUCINE (INTERACTIVE)

2. POLAR (BUT NEUTRAL) SIDE CHAINS
SERINE (INTERACTIVE)

3. POSITIVE SIDE CHAINS AT pH = 7 (BASIC)
HISTIDINE (INTERACTIVE))

4. NEGATIVE SIDE CHAINS AT pH = 7 (ACIDIC)
ASPARTIC ACID (INTERACTIVE))

NOMENCLATURE

COMMON NAMES NOT IUPAC

ABBREVIATE
• ALA = ALANINE

• SER = SERINE

• TYR = TYROSINE

ADDITIONAL THREE DIMENSIONAL VIEWS OF AMINO ACIDS

PROPERTIES

• HIGH MELTING POINTS
  ABOVE 250^o

• SOMEWHAT SOLUBLE IN WATER

• INSOLUBLE IN NONPOLAR SOLVENTS

• MIGRATE IN AN ELECTRIC FIELD
  • EXCEPT AT A CERTAIN pH CALLED THE ISOELECTRIC POINT (pI)

HOW?

EXISTS AS A DIPOLAR ION OR ZWITTERION
• TITRATION CURVE

• FOR MOST AMINO ACIDS
  APPROXIMATE pK_a OF -CO₂H IS 2-2.3
  APPROXIMATE pK_a OF -NH₃¹⁺ IS 9-10

• ISOELECTRIC POINT IS A FUNCTION OF STRUCTURE

• MAKES FOR A SEPARATION TECHNIQUE: ELECTROPHORESIS

PREPARATION, MORE

• THESE AMINO ACIDS ARE RACEMIC
• MUST BE RESOLVED

REACTIONS