Diverse Macromolecules
V. proteins are macromolecules that are
polymers formed from amino acids
monomers
A. proteins have great structural diversity and
perform many roles
B. roles include enzyme catalysis, defense,
transport, structure/support, motion, regulation;
protein structure determines protein function
C. proteins are polymers made of amino acid
monomers linked together by peptide bonds
1. amino acids consist of a central or alpha carbon;
bound to that carbon is a hydrogen atom, an
amino group (-NH2), a carboxyl group (-COOH),
and a variable side group (R group)
• the R group determines the identity and much of
the chemical properties of the amino acid
• there are 20 amino acids that commonly occur
in proteins; pay attention to what makes an R
group polar, nonpolar, or ionic (charged) and
thus their hydrophobic or hydrophilic nature
• plants and bacteria can usually make their own
amino acids; many animals must obtain some
amino acids from their diet (essential amino
acids)
2. the peptide bond joins the carboxyl group of one
amino acid to the amino group of another; is formed
by a condensation reaction
2. two amino acids fastened together by a peptide
bond is called a dipeptide, several amino acids
fastened together by peptide bonds are called a
polypeptide
D. the sequence of amino acids determine the
structure (and thus the properties) of a protein
E. proteins have 4 levels of organization or structure
1. primary structure (1) of a protein is the sequence of
amino acids in the peptide chain
2. secondary structure (2) of a protein results from hydrogen
bonds involving the backbone, where the peptide chain is
held in structures, either a coiled α-helix or folded β-pleated
sheet; proteins often have both types of secondary structure
in different regions of the chain
3.
tertiary structure (3) of a protein is the
overall folded shape of a single polypeptide
chain, determined by secondary structure
combined with interactions between
4. quaternary structure (4) of a protein results from
interactions between two or more separate
polypeptide chains
• the interactions are of the same type that produce 2
and 3 structure in a single polypeptide chain
• when present, 4 structure is the final threedimensional structure of the protein (the protein
conformation)
• example: hemoglobin has 4 polypeptide chains
• not all proteins have 4 structure
Tertiary Structure of Hemoglobin
5. ultimately the secondary, tertiary, and quaternary
structures of a protein derive from its primary
structure, but molecular chaperones may aid the
folding process
6. protein conformation determines function
7. denaturation is unfolding of a protein, disrupting 2,
3, and 4 structure
• changes in temperature, pH, or exposure to various
chemicals can cause denaturation
• denatured proteins typically cannot perform their
normal biological function
• denaturation is generally irreversible
F. enzymes are biological substances that regulate
the rates of the chemical reactions in living
organisms; most enzymes are proteins (covered in
some detail later in this course)
G. “related compounds” –amino acids; modified
amino acids; polypeptides too short to be
considered true proteins; and modified short
polypeptides