Download Biochemistry Chapter 17

Biochemistry Chapter 17
Protein
Protein

What does protein do in the body?
Protein
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Most people think of building
muscle but protein has many
functions in the body.
The human body contains
between 10,000 to 50,000
different proteins.
Only 1,000 have been
studied in detail.
Macromolecules

Protein molecules are
very big and contain
LOTS of atoms so
they are called
macromolecules.
Elements of Proteins
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Protein molecules consist
of carbon, hydrogen,
oxygen, nitrogen, and
sometimes other
elements.
The nitrogen atoms make
proteins so variable and
different from lipids and
carbohydrates.
Structure of a protein
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Protein is made of
chains of substances
called amino acids.
Amino acids are
organic compounds
that contain a
carboxyl group and
an amine group.
Amine Group
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The amine group
consists of one
nitrogen atom and
two hydrogen atoms.
It is written –NH2
Peptide Bonds
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Amino acids combine in long chains to form
proteins.
Amino acids attach together through peptide
bonds.
Peptide bonds occur between the amine group
on one AA and the carboxyl group on another
AA.
Water is removed and the carbon bonds to the
nitrogen.
Polypeptide
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When ten or more
amino acids are
chained together in a
single molecule, we
call that a
polypeptide.
Most proteins contain
hundreds of AA and
many contain
thousands.
Structure of Proteins
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Peptide bonds cause
AA to combine in long
chains.
Protein molecules
tend to coil, fold, and
tangle in complex
shapes
Hydrogen Bonds
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Hydrogen bonds
between parts of the
peptide chain cause
the molecule to fold
and coil in a particular
way.
Some proteins form
spirals or rope-like
structures.
Structure and Function
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A protein’s shape
helps determine its
function.
Rope-like, “fibrous”
proteins serve as
connective tissue in
the body.
Collagen and elastin
are two fibrous
proteins.
Structure and Function
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More compact,
“globular” proteins act
as carrier molecules.
Hemoglobin carries
oxygen in the blood.
Denaturation
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The tightly coiled shape of proteins
prevents them from dissolving in water.
Denaturation is a chemical process that
changes the shape of a protein without
breaking the peptide bonds.
Denaturation breaks the hydrogen bonds
and causes the protein to uncurl.
Denaturation
Methods of Denaturation
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Heat- think of how eggs and meat change
as they cook
Mixing or kneading
pH
Freezing
Pressure
Chemical compounds like metal ions
Coagulation

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Coagulation changes
a liquid into a soft,
semisolid clot or solid
mass.
Coagulation occurs
when a denaturated
protein reforms some
hydrogen bonds.
Scrambled eggs are a
good example.
Protein in Food
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What types of food contain protein?
Eggs
Meat
Fish
Poultry
Legumes (beans)
Nuts and seeds
Eggs
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Eggs are complex biological systems that
contain almost every vitamin and mineral
you need.
The egg white or albumen contains lots of
protein (ovalbumin) and not much else.
The egg yolk contains all of the fat and
most of the other nutrients found in eggs.
It is also high in protein (livetin).
Meat and Fish
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Animal muscle fiber is about 20% protein.
Meat contains a large amount of
connective tissue and can be very tough if
not cooked properly.
Fish has much less connective tissue and
cooks very quickly.
Protein from Plants
Nuts and seeds are
high in protein but
also high in fat.
 Soybeans are 40%
protein and contain
polyunsaturated fats.

Protein in Cooking
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Many amino acids can
combine with both
fats and water and
are called emulsifiers.
Egg yolks are the
most common
emulsifiers used in
cooking.
Gelatin
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Gelatin is made from the collagen in
animal connective tissue.
Gelatin is used to thicken everything from
meat sauces to desserts.
The long proteins in gelatin form a
network that locks in water to form gels.
Gluten
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Gluten is an elastic
substance formed by
mixing water with the
proteins found wheat.
Kneading dough helps
to develop gluten and
makes the dough
springy and stretchy.
Protein in the Body
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Proteins are denatured by hydrochloric
acid in the stomach and then broken down
by enzymes in the small intestine.
Individual amino acids are carried through
the blood stream to the cells where they
are reassembled into needed proteins.
Functions of body Proteins
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Providing structure
New Growth
Enzymes and
hormones
Transporting nutrients
Functions of body Proteins
Antibodies to ward off
disease
 Stabilizing pH levels
 Can provide energy in
an emergency
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Essential Amino Acids

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There are 20 amino
acids used by the
body.
Our bodies are
capable of making 11
of those.
The other 9 must be
eaten and are called
essential amino acids.
Complete Protein
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A complete protein contains all 9 essential
amino acids.
An incomplete protein does not.
A high-quality protein like egg protein
contains all the essential amino acids in
the correct amounts.
Dietary Allowances
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Protein is an essential part of the diet but
we only need relatively small amounts.
An adult needs to eat only about 50g of
protein in one day.
Most Americans eat more than that in one
meal.