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Biology 107
Macromolecules II
September 8, 2003
Macromolecules II
Student Objectives: As a result of this lecture and the assigned
reading, you should understand the following:
1. Proteins are biological polymers constructed from amino acid
monomers. Each different protein has a unique structure and
function, and protein diversity is based upon these different
arrangements of a universal set of amino acids.
2. There are seven major functional classes of proteins: 1) structural
proteins; 2) contractile proteins; 3) storage proteins; 4) defense
proteins 5) transport proteins 6) signaling proteins 7) enzymes.
Macromolecules II
.
Amino acids have the same basic structure, with the amino group
and carboxyl group bonded to a central C atom (the alpha C).
This central carbon also has an attached H atom and a chemical
group called the "R" group.
4.
It is the "R" group that is the variable part of the amino acid and
determines the specific properties of each of the 20+ amino acids
in proteins.
5.
Amino acids are linked together by dehydration synthesis, with the
resulting covalent linkages called peptide bonds.
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Macromolecules II
6. The specific shape that determines a protein's function comprises
four (4) successive levels of structure, each determined by the
previous level.
a.
The primary structure is the sequence of amino acids forming
the polypeptide chain.
b.
The secondary structure consists of polypeptide chain coils or
folds held in place by hydrogen bonding between the - N - H
and the - C = O groups along the backbone of the chain.
Coiling or folding of a polypeptide chain usually results in one
of two repeating structures, either an alpha-helix or a betapleated sheet.
Macromolecules II
c.
Tertiary structure is the overall 3-dimensional shape of a
polypeptide; tertiary structure is maintained by bonding (hydrogen,
ionic and covalent [disulfide bridges]) and hydrophobic or
hydrophilic interactions between the "R" groups of various amino
acids in the polypeptide chain.
d.
Quaternary structure is produced by the bonding interactions of
two (2) or more polypeptide subunits. Quaternary structure is
maintained by hydrogen bonding, ionic interactions, and
hydrophobic interactions.
Structure of Amino Acids with Nonpolar “R” Groups
Structure of Amino Acids with Polar or Ionic “R”
Groups
Primary Protein
Structure
Consist of sequence of amino acids
Has a polarity – amino end (#1 amino
acid of the chain) and carboxyl
end
Dictates the other levels of folding
and structure
Secondary Protein Structure
Bonds That Stabilize Tertiary Structure
Quaternary Protein Structure
Summary of Levels of Protein Structure
Effects of Altered Protein Structure on Function