BIOMOLECULES
PROTEIN
“PROTEIOS”
FUNCTIONS:
Structural support; enzymes;
movement; transport; recognition
and receptor molecules;
regulation of proteins and DNA;
hormones; antibodies; toxins and
venoms
Proteins are macromolecules –
polymers of amino acid
monomers, which contain both
an amino and a carboxyl group
Amino Acids
• All organisms use 20 different
amino acids to build proteins
• Most have the same structural plan:
a central carbon atom is attached to
an amino group (NH2), a carboxyl
group (COOH), a hydrogen atom,
and a variable R group:
 Amino acids bond covalently to form
peptides and polypeptides
 Peptide bonds happen between the
terminal carboxyl of one amino acid and
terminal amino group of the next amino
acid.
 A dehydration synthesis reaction occurs
and forms the peptide bond.
A Peptide Bond
Side
group
Amino
group
Carboxyl
group
Amino
acid 1
Nterminal
end
Cterminal
end
Peptide bond
Amino
acid 2
Peptide
A Disulfide Linkage
Disulfide bond happens between two terminal
sulfhydrils of different amino acids
Amino
acid
backbo
ne
chains
Oxidation of the
—SH groups of
two cysteine
amino acids
covalently joins
the two sulfur
atoms to form a
disulfide linkage.
Nonpolar Amino Acids
Alanine
Ala
A
Phenylalanine
Phe
F
Valine
Val
V
Tryptophan
Trp
W
Leucine
Leu
L
Isoleucine
Ile
I
Methionine
Met
M
Proline
Pro
P
Glycine
Gly
G
DISCLAIMER: This document is a draft and the information contained herein is subject to change as this document is currently undergoing review. The final
version of this teacher’s resource manual will be published as soon as the review has been completed.
Uncharged Polar Amino Acids
Cysteine
Cys
C
Threonine
Thr
T
Tyrosine
Tyr
Y
Asparagine
Asn
N
Glutamine
Gln
Q
Serine
Ser
S
DISCLAIMER: This document is a draft and the information contained herein is subject to change as this document is currently undergoing review. The final
version of this teacher’s resource manual will be published as soon as the review has been completed.
Charged Amino Acids
Aspartic acid
Asp D
Glutamic acid
Glu E
Charged Amino Acids
Lysine Lys
K
Arginine Arg
R
Histidine His
H
Four Levels of Protein Structure
 Primary structure is the unique sequence
of amino acids forming a
polypeptideChanging even a single amino
acid alters secondary, tertiary, and
quaternary structures – which can alter or
destroy the biological function of a protein
DISCLAIMER: This document is a draft and the information contained herein is subject to change as this document is currently undergoing review. The final
version of this teacher’s resource manual will be published as soon as the review has been completed.
Example: Substitution of a single amino acid
in hemoglobin produces an altered form
responsible for sickle-cell disease
 Secondary structure is produced by
the twists and turns of the amino acid
chain
 Tertiary structure is the folding of the
amino acid chain, with its secondary
structures, into the overall 3Dshape of
a protein
 Quaternary structure, when present,
is formed from more than one
polypeptide chain
A. Primary structure:
the sequence of amino
acids in a protein
B. Secondary structure:
regions of alpha helix,
beta strand, or random
coil in a polypeptide chain
C. Tertiary structure:
Heme overall three-dimensional
group folding of a polypeptide
chain
β-Globin
β-Globin
polypeptide polypeptide
D. Quaternary
structure:
the arrangement of
polypeptide chains
in a
protein that contains
more than one chain
α-Globin
polypeptide
α-Globin polypeptide
What Determines Protein Conformation
Unfolding a protein from its active
conformation so that it loses its
structure and function (caused by
chemicals, changes in pH, or high
temperatures) is called
denaturation
For some proteins, denaturation is
permanent – for others,
denaturation is reversible
(renaturation)
ENZYMES
 Are biological catalysts
 They speeds up the rate of chemical
reactions by lowering its activation
energy
MODELS OF ENZYME ACTION
Lock And Key Model
 Enzymes are specific. This high specificity
of enzymes can be explained by this lock
and key model.
 According to the lock and key model,
enzymes will only act upon a specific
substrate.
Enzyme molecules contain a special pocket or cleft called the
active sites.
In enzymatic reactions, the substance at the beginning of the
process, on which an enzyme begins it’s action is called
substrate.
Induced Fit Model
 When the active site on the enzyme
makes contact with the proper substrate,
the enzyme molds itself to the shape of
the molecule.
ENZYME STRUCTURE
 Apoenzyme – an inactive enzyme
 Co-factor – a mineral that activates the
enzyme
 Active site – the site where the substrate
will bind
 Coenzyme – a vitamin subsituent that acts
as a cofactor that activates an enzyme