CHEM 142_N (LECTURE) : PROTEINS
CHARACTERISTICS OF PROTEINS
Account for 15% of a cell’s overall
mass
Contain CHON/S(carbon, hydrogen,
oxygen, nitrogen, sulfur)
Nitrogen is always present in
protein, unlike in carbohydrates and
lipids
Nitrogen content: 15.4 %
Specialized proteins like casein and
hemoglobin contain phosphorus
and iron, respectively
Naturally occurring, unbranched
polymer
Monomer units: amino acids
I. AMINO ACIDS: THE BUILDING
BLOCKS FOR PROTEINS
An organic compound
Contains an amino group(-NH2)
and carboxyl group(-COOH)
amino acids found in proteins are
always a-amino acids
a-amino acids
-(-NH2) & (-COOH) are always
attached to a-carbon atom
General formula:
R-GROUP
-Aka amino acid side chain
-Distinguishes a-amino acids from
each other
-Vary in size, charge, acidity,
functional groups present, h-
bonding ability, chemical
reactivity
STANDARD AMINO ACID
- 20 a-amino acids found in
proteins
4 Classification Based On The Side-
Chain Polarity
1) NONPOLAR
2) POLAR NEUTRAL
3) POLAR ACIDIC
4) POLAR BASIC
ESSENTIAL AMINO ACID
- 9 amino acids
- Must be obtained from dietary
sources
COMPLETE DIETARY PROTEIN
-Protein that contains all essential
amino acids
- E.g. milk, meat, fish, eggs, soy
protein
