Proteins
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Proteins:
Multipurpose molecules
Regents Biology
2006-2007
Functions of proteins/amino acids:
structural– claws, nails, hair, hooves (keratin),
outer layer of skin (collagen)
 transport - hemoglobin, cell membrane transport
proteins
 movement contractile proteins actin & myosin
 regulatory - hormones
 catalytic – enzymes that speed up reactions
allowing them to occur
 immunological – antibodies, antigens on the
hemoglobin
exterior of a cell
 storage of amino acids
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collagen (skin)
Proteins
 Building block = amino acids
amino amino amino amino amino
acid – acid – acid – acid – acid

20 different amino acids
H O
H
| ||
—N—
—C—C—OH
|
H variable
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group
General structure of an amino acid
R group
R
H
N
H
C
H
O
C
OH
amino group
carboxyl group
(basic)
(acidic)
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There are 20 amino acids naturally incorporated into
proteins
Alanine
Arginine
Asparagine
Aspartic acid
Cysteine
Glutamic acid
Glutamine
Glycine Histidine
Isoleucine
Leucine
Lysine
Methionine
Phenylalanine
Proline
Serine
Threonine
Tryptophan
Tyrosine
Valine
You do NOT need to know their names!
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I
Other amino acids do exist…
I
Thyroxine:
used in the human
body as a hormone I
to regulate
metabolic rate
…but are not normally found in
proteins
I
CH2
H
N
H
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O
C
H
O
C
OH
Humans can synthesis some amino acids by altering other
amino acids, however…
…some amino acids cannot be synthesised and are
therefore needed in the diet.
These are the essential amino acids
Arginine
Histidine
Isoleucine
Leucine
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Lysine
Methionine
Phenylalanine
Threonine
Tryptophan
Valine
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Phenylketonuria or
Maple Syrup Urine Disease
Patients lack the enzyme
phenylalanine hydroxylase – needed
to dispose of the amino acid phenylalanine properly
Penylalanine rapidly builds up in the blood stream
- it converted to unusual metabolites which give
the patient’s urine a characteristic smell
- it also rapidly causes brain damage!
Treatment: A diet low in phelylalanine
No meat, fish, poultry, eggs, cheese, milk, beans, or peas
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Water-fearing amino acids
 Hydrophobic
“water fearing” amino acids
 try to get away from water in cell

 the protein folds
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Different amino acids have different R groups
Their different properties depend on their R groups
Hydrophobic
(‘Water-hating’) R groups
CH3
H
N
H
alanine
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C
H
O
C
CH2
H
N
OH
C
O
C
H
OH
H
phenylalanine (aromatic)
Water-loving amino acids
 Hydrophillic
“water loving” amino acids
 try to stay in water in cell

 the protein folds
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Hydrophillic
(‘Water-loving’) R groups
SH
OH
CH2
H
N
C
H
H
cysteine
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O
CH2
H
C
N
OH
H
C
H
serine
O
C
OH
Amino acid chains
 Proteins

amino acids chained into a polymer
amino acid
amino acid
amino acid
amino acid
amino acid
 Each amino acid is different

some “like” water & dissolve in it

some “fear” water & separate from it
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Formation of a dipeptide: carboxyl group of one amino
acid reacts with amino group of second amino acid
R1
H
N
H
C
O
R2
H
C
N
OH
H
C
H
C
OH
H
H2O
H
N
H
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R1
O
H
R2
C
C
N
C
H
H
peptide linkage
O
C
O
water
molecule
formed
a dipeptide
OH
Formation of a
dipeptide produces
a molecule of
water, therefore…
R1
H
N
H
C
O
C
N
OH
H
R2
H
H
C
O
C
OH
H
H 2O
…this is a
condensation
reaction
H
N
H
R1
O
H
R2
C
C
N
C
H
H
2 amino acids  dipeptide + water
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O
C
OH
Splitting a dipeptide
to form two amino
acids consumes
one molecule of
water, therefore…
H
N
H
R1
O
H
R2
C
C
N
C
H
O
C
OH
H
H 2O
R1
H
…this is a
hydrolysis reaction
N
H
C
H
O
R2
H
C
N
OH
H
dipeptide + water  2 amino acids
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C
H
O
C
OH
3-D protein structure
 Proteins fold & twist into 3-D shape

that’s what happens in the cell!
hemoglobin
growth
hormone
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pepsin
collagen
Its shape that matters!
 Proteins do their jobs, because
of their shape
 Unfolding a protein destroys its shape
wrong shape = can’t do its job
 unfolding proteins = “denature”

 temperature
 pH (acidity) folded
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unfolded
“denatured”
Let’s eat some
Proteins!
Regents Biology
2006-2007