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General Info about Proteins
 Most diverse and most
important
macromolecules.
 Our entire DNA codes
for proteins only, and
nothing else. Therefore
they are involved in
everything cells do.
Protein Structure
 Proteins are polymers of
amino acids folded into a
specific 3D shape that
belays its function.
 Amino acids are made up
of a central carbon atom
connected to an amino
group, carboxyl group, a
hydrogen atom and an R
group (side chain).
Amino Acids
 Amino acids are considered to
be amphiprotic because they
possess both an acidic terminus
(carboxyl group) and a basic
terminus (amino group).
 Humans use 20 different amino
acids, so there are twenty
different R-groups (shown on
pages 42-43).
 8 of these amino acids are
known as essential amino acids
because our body cannot make
them from simpler substances,
so we must get these amino
acids from our diet.
Amino Acids
 Amino acids can be
classified based on their
R group in two main
ways:
By polarity: polar
(water-soluble) versus
non-polar (lipid
soluble)
ii) By electric charge:
acidic (negatively
charged) versus basic
(positively charged)
i)
Linking Amino Acids to make a
Protein
 All proteins have a specific
shape, unique to that protein.
This final shape is known as
the conformation of the
protein and it depends
entirely upon the amino acid
sequence the protein
contains.
 In protein synthesis (the
making of proteins), DNA
directs the ribosomes, RNA
and enzymes to start linking
amino acids together in a
specific sequence (Unit 3).
Linking Amino Acids to make a
Protein
 The joining of amino acids
together is another example of a
dehydration synthesis reaction.
The linkage between two amino
acids is known as a peptide
bond.
 The growing polypeptide chain
will always have an amino
terminus (A-terminus) and a
carboxyl terminus (C-terminus).
 All specific proteins have the
same exact polypeptide
sequence (i.e. all insulin
proteins contain the exact same
polypeptide sequence), which is
determined by DNA.
Globular Proteins
 Globular proteins are
composed of one or
more polypeptide chains
that have a rounded,
spherical conformation.
 Globular proteins have
four levels of structure:
(p. 44 and/or handouts
for diagrams)
Space filling and ribbon models of lysozyme, a protein
assembled from 129 amino acids.
• The primary structure of a protein is the
sequence of amino acids dictated by DNA.
met-enkephalin
tyr-gly-gly-phe-met
leu-enkephalin
tyr-gly-gly-phe-leu
oxytocin
gly-leu-pro-cys-asn-gln-Ile-tyr-cys
vasopressin
gly-arg-pro-cys-asn-gln-phe-tyr-cys
Sickle cell anemia is due to a single amino acid
substitution in the primary structure of hemoglobin
Lysozyme
Coiling and folding of the
amino acid chain defines a
protein’s secondary structure.
This secondary structure is due
to hydrogen bonds between
adjacent portions of the
polypeptide chain.
Stereo image of α-helix
The tertiary structure of the protein is based upon the
interactions between the R groups of amino acids. As shown
in the diagram below, there are four main interactions between
R groups of different amino acids.
Stereo image of insulin
Stereo image of cytochrome c
Cytochrome c. Hydrophilic side chains are shown in green and are located mainly
on the surface of the protein where they come in contact with the aqueous
cytoplasm. Hydrophobic side chains are shown in red are primarily located within
the interior of the protein.
The association of two or more polypeptide chains to
form a functional protein constitutes the quaternary
structure of a protein.
Collagen
Hemoglobin