Download notes- 3. protein

3. Proteins
types are:
– structural proteins
(collagen in bones
and keratin in hair)
– contractile proteins (in muscles)
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– transport proteins
(hemoglobin)
– immunity proteins
(antibodies)
– Communication
(hormones)
–  enzymes
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
a) structure
a protein is a polymer constructed of amino acid
monomers
- a polypeptide is a chain of amino acids. Once
this chain folds into a unique 3-D shape, it
becomes a protein.
-contain C, H, O, N
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Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
•  There are 20 types of amino acids, 9 are
essential, that is animals cannot synthesize
them
ESSENTIAL
AMINO ACIDS
– these 9 are easily
obtained from
animal protein
Methionine
Valine
(Histidine)
– They can also be
obtained from the
proper combination
of plant foods
Threonine
Phenylalanine
Corn
Leucine
Isoleucine
Tryptophan
Beans and
other
legumes
Lysine
Figure 21.16
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b) protein digestion
Enzymes break proteins down to amino acids
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c) Deamination: breakdown of amino acids
•  occurs in the liver
•  deamination removes the nitrogen group from
the amino acid and creates two products:
– urea ---> excreted as waste (urine)
– glucose ---> cellular respiration
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
d) Denaturation: polypeptide chains unravel,
protein loses its specific shape and as a result,
its function
•  caused by heat, changes in salt concentration
and pH
•  eg: frying an egg
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e) Diagnostic Tests for the Presence of Proteins in
Food
•  Biuret Reagent: CuSO4 and NaOH
•  when proteins are present, the reagent turns
from blue to purple or pink
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