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NUTRITION FOR HEALTH
SCIENCES
PROTEIN
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PROTEIN
When mighty roast beef was the Englishman’s food,
It ennobled our hearts and enriched our blood,
Our soldiers were brave and our courtiers were good.
Oh! the roast beef of old England!
Richard Leveridge
(1670-1758)
English singer and composer
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PROTEIN
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PROTEIN
DEFINITION
Proteins are compounds
composed of carbon,
hydrogen, oxygen, and
nitrogen atoms
arranged into amino
acids linked in a chain.
Some amino acids also
contain sulfur atoms
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PROTEIN
AMINO ACIDS
Amino Acids are compounds that serve as the
building blocks of proteins; each contains
an amino group, an acid group, a hydrogen
atom, and a distinctive side group attached
to a central carbon atom
– Nine essential amino acids
– Thirteen non-essential amino acids
– Some are able to be manufactured by chemists
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PROTEIN
AMINO ACIDS
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PROTEIN
AMINO ACIDS
Essential Amino Acids -- Amino Acids that
the body cannot synthesize in amounts
sufficient to meet physiological need
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PROTEIN
AMINO ACIDS
Essential Amino Acids
Valine
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PROTEIN
AMINO ACIDS
Essential Amino Acids
Leucine
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PROTEIN
AMINO ACIDS
Essential Amino Acids
Isoleucine
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PROTEIN
AMINO ACIDS
Essential Amino Acids
Threonine
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PROTEIN
AMINO ACIDS
Essential Amino Acids
Lysine
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PROTEIN
AMINO ACIDS
Essential Amino Acids
Sulfur Containing Amino Acids
(Grouped together because if the body has enough
Methionine, it can change it into Cysteine)
Methionine
Cysteine (non-essential)
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PROTEIN
AMINO ACIDS
Essential Amino Acids
Aromatic Amino Acids (contain benzene ring)
(Grouped together because if the body has enough
Phenylalanine, it can change it into Tyrosine)
Phenylalanine Tyrosine (non-essential)
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PROTEIN
AMINO ACIDS
Essential Amino Acids
Tryptophan
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PROTEIN
AMINO ACIDS
Essential Amino Acids
Histidine
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PROTEIN
AMINO ACIDS
Essential Amino Acids
• Need to be obtained from foods
• Sometimes a non essential amino acid
can be come essential -- Examples
– Illness can demand requirements beyond the
body’s ability to produce the amino acid
– In Phenylketonuria (PKU) the body is unable to
convert phenylalanine to tyrosine, therefore
tyrosine becomes essential
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PROTEIN
AMINO ACIDS
Non-essential Amino Acids -- Amino Acids
that the body is able to manufacture
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PROTEIN
AMINO ACIDS
Non-essential Amino Acids
• Alanine
• Arginine
• Asparagine
• Aspartic Acid
• Cystine
• Glutamic Acid
• Glutamine
• Glycine
• Proline
• Serine
• Tyrosine
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PROTEIN
SURFACE STRUCTURE
• Have a great variety of surface structures
(shapes) to perform distinct, individual, and
specialized functions
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PROTEIN
SURFACE STRUCTURE
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PROTEIN
SURFACE STRUCTURE
Ala
Human insulin is identical to pig insulin, except that the last amino acid of
the B-chain for the pig is alanine (Ala) instead of threonine (Thr)22
PROTEIN
• The average amino acid weighs 6.25 times
as much as the nitrogen it contains,
therefore
• Nitrogen represents 16% of the weight of
the protein
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PROTEIN
DIGESTION AND ABSORPTION
• Role of protein is not to provide the body
with proteins, but to supply amino acids
from which the body can make protein
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PROTEIN
HCl
DIGESTION AND
ABSORPTION
• Hydrolysis of proteins
begins in the stomach
– HCl uncoils
(denatures) the
protein’s tangled
strand so that digestive
enzymes can attack
the peptide bonds
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PROTEIN
DIGESTION AND
ABSORPTION
Pepsin
Proteases
– Pepsin (a gastric protease)
cleaves proteins -- large
polypeptides are broken down
into smaller polypeptides
– When these polypeptides enter
the small intestine pancreatic
and intestinal proteases
hydrolyze them further into
short peptide chains
(oligopeptides) tripeptides,
dipeptides, and amino acids
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PROTEIN
DIGESTION AND
ABSORPTION
– Peptidase enzymes on the
surface of the intestinal cells
break more of the peptide
bonds
– A mixture of free amino
acids, dipeptides, and
tripeptides is left
– Distinct carriers then
transport these pieces across
the intestinal cells for
passage into the blood
Absorption
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PROTEIN
PROTEINS IN THE BODY
Functions
Enzymes
• Enzymes are proteins that facilitate
chemical reactions without being changed
in the process
• Are essential to all life processes
• Are protein catalysts
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PROTEIN
PROTEINS IN THE BODY
Functions
Enzymes (continued)
• Act upon other proteins
– You eat protein
– Digestive enzymes (proteins) break down protein into
amino acids
– Amino acids enter the cells where proteins (enzymes)
put them together into long chains whose sequence is
specified by genes
– Chains fold and twist themselves to form proteins;
some of these proteins become enzymes themselves
– These enzymes may then be used to break apart or put
together other compounds
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PROTEIN
PROTEINS IN THE
BODY
Functions
Fluid Balance
• Fluids are present in
several body
compartments
– Spaces inside blood
vessels
– Spaces within the cells
(outside the blood
vessels)
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PROTEIN
PROTEINS IN THE BODY
Functions
Fluid Balance (continued)
• Fluids go back and forth in these spaces
and proteins (together with minerals) help
to maintain the needed distribution of
these fluids
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PROTEIN
PROTEINS IN THE BODY
Functions
Fluid Balance (continued)
– Proteins are large
– Proteins are attracted to water (hydrophilic)
– Being large, proteins cannot pass freely across cell
membranes that separate body compartments
– Attracting water makes proteins even larger
– A cell wants to keep a certain amount of water in its
interior space but can’t manufacture the water directly
– The cell can manufacture protein and these proteins
will hold water
– Therefore, the cell uses proteins to regulate the
distribution indirectly
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PROTEIN
PROTEINS IN THE BODY
Functions
Acid-Base Balance
• Acids are compounds that release hydrogen
ions in solution
• Bases are compounds that accept hydrogen
ions in a solution
• Acid-Base Balance is the equilibrium in the
body between acid and base concentrations
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PROTEIN
PROTEINS IN THE BODY
Functions
Acid-Base Balance (continued)
• Normal body processes continually produce
acids and bases, which must be carried by
the blood to the organs of excretion
• Blood must do this without allowing its own
acid-base balance to be affected
• Proteins act as buffers, picking up
hydrogens (acid) when there are too many
and releasing them when there are too few
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PROTEIN
PROTEINS IN THE BODY
Functions
Acid-Base Balance (continued)
• Acidosis
– Results when the blood pH limit falls below
7.35 and causes proteins to undergo
denaturation -- they loose their shape and
ability to function
– Disturbing a protein’s shape renders it useless
e.g. hemoglobin looses its capacity to carry
oxygen (if unchecked, can be fatal)
• Alkalosis
– Results when the blood pH limit rises above
7.45
– Can cause coma or death
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PROTEIN
PROTEINS IN THE BODY
Functions
Acid-Base Balance (continued)
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PROTEIN
PROTEINS IN THE BODY
Functions
Acid-Base Balance (continued)
• By accepting and releasing hydrogen ions,
proteins act as buffers maintaining acidbase balance of the blood and body fluids
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PROTEIN
PROTEINS IN THE
BODY
Functions
Antibodies
• Antibodies are large
proteins of the blood and
body fluids, produced by
the immune system in
response to the invasion
of the body by foreign
molecules (usually
proteins called antigens)
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PROTEIN
PROTEINS IN THE BODY
Functions
Antibodies (continued)
• Combine with and inactivate the foreign
invaders, thus protecting the body
• Act against viruses, bacteria, and other
disease agents
• Without adequate protein, the body cannot
maintain its resistance to disease
(immunity)
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PROTEIN
PROTEINS IN THE BODY
Functions
Hormones
• Hormones are messenger
molecules
• Are secreted by a variety of
endocrine glands in response
to altered conditions in the
body
• Each travels to one or more
specific target tissues or
organs where is elicits a
specific response
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PROTEIN
PROTEINS IN THE BODY
Functions
Hormones (continued)
• Some are made up of amino acids (others
are sterols such as testosterone)
• Examples
– Insulin and glucagon help regulate the blood
glucose
– The thyroid hormone helps regulate the body’s
basal metabolic rate
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PROTEIN
PROTEINS IN THE BODY
Functions
Transport Proteins
• Some act as pumps picking up compounds
on one side of cell membranes and
depositing them on the other side
• Others move about in body fluids carrying
nutrients and other molecules from one
organ to another
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PROTEIN
PROTEINS IN THE
BODY
Functions
Transport Proteins
(continued)
• Examples
– Hemoglobin -- carries
oxygen from the lungs
to the body’s cells
– Lipoproteins transport
lipids around the body
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PROTEIN
PROTEINS IN THE BODY
Functions
Blood Clotting
• Fibrin, a stringy insoluble mass of protein
fibers, facilitates blood clotting
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PROTEIN
PROTEINS IN THE BODY
Functions
Visual Pigments
• Opsin, the protein portion of
the visual pigment molecule
in the cells of the retina,
responds to light by
changing its shape thus
initiating the nerve impulses
that convey the sense of
light to higher brain centers
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PROTEIN
PROTEINS IN THE BODY
Functions
Structural Proteins
• Collagen
– Is the main fibrous protein
(others are elastin and
keratin)
– Helps make scar tissue,
forms the matrix of bones
and teeth
– Forms the material of
ligaments and tendons
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PROTEIN
PROTEINS IN THE BODY
Pressure Sores
• Also known as decubitus ulcers, bed sores
• Caused by
– Unrelieved pressure on the skin and underlying
tissues
– Friction (being pulled across bed sheets)
– Shear (sliding down in a bed or chair causing the skin
to fold over itself and cutting off blood supply)
– Poor nutrition, especially protein, may lead to skin
breakdown
• Four stages
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PROTEIN
PROTEINS IN THE BODY
Pressure Sores
• Stage 1
– Redness and heat over a pressure point
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PROTEIN
PROTEINS IN THE BODY
Pressure Sores
• Stage 2
– Destruction of the epidermis and partial
destruction of the dermis
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PROTEIN
PROTEINS IN THE BODY
Pressure Sores
• Stage 3
– All the layers of the skin are destroyed and a deep
crater forms
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PROTEIN
PROTEINS IN THE BODY
Pressure Sores
• Stage 4
– Ulcer extends through the skin and subcutaneous
tissues and may involve bone, muscle, and other
structures.
– Patient experiences fluid loss, pain, and is at great
risk for infection.
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PROTEIN
PROTEINS IN FOODS
• Role is not to supply the body protein
directly but to supply amino acids from
which the body can make its own protein
• Protein Quality
– Complete Protein is a protein that contains all
the amino acids essential in human nutrition in
amounts adequate for human use
• Must contain the nine essential amino acids and
enough nitrogen and energy for the synthesis of the
other thirteen
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PROTEIN
PROTEINS IN FOODS
• Protein Quality (continued)
• Body makes only complete proteins
– Body uses amino acids in a specific ratio to one another
– If one amino acid is supplied in an amount smaller than
needed, synthesis will be limited
» Concept of the limiting amino acid
» A chain is only as strong as its’ weakest link
» The limiting amino acids are the sulfur containing
ones (methionine and cysteine), tryptophan, and
lysine-- these are a little harder to get than the others
• Dietary protein will not be used efficiently when
energy from carbohydrate and fat is lacking (protein
sparing effect of carbohydrate and fat)
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PROTEIN
PROTEINS IN FOODS
• Protein Quality (continued)
• Generally, proteins from animals is
complete protein (exception is gelatin)
• Plant protein is variable
– Corn protein is incomplete
– Soy protein is complete
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PROTEIN
PROTEINS IN FOODS
• Protein Quality (continued)
• Complementary Protein -- two or more
proteins whose amino acid assortments
complement each other in such a way such
that the essential amino acids missing from
one are supplied by the other
– The educated vegetarian can choose a diet that is
adequate in protein by choosing a variety of
legumes, grains, and vegetables
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PROTEIN
PROTEINS IN FOODS
• Protein Quality (continued)
– Digestibility
• Digestibility is a measure of the amount of amino
acids absorbed from a given protein intake
• High quality protein is an easily digestible complete
protein
– Reference Protein
• Egg protein
• Used by the Food and Agriculture Organization
(FAO) and World Health Organization (WHO) as a
standard against which to measure the quality of
other proteins
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PROTEIN
PROTEINS IN FOODS
SOURCES
• Milk -- 8 grams per cup
• Meat -- 7 grams per ounce
• Vegetables -- 2 grams per 1/2 cup
• Starch/bread -- 3 grams per serving
• Fruits -- negligible
• Fats -- negligible
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PROTEIN
PROTEINS IN FOODS
SOURCES
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PROTEIN
HEALTH EFFECTS OF PROTEIN
• Protein Energy Malnutrition (PEM)
– Protein Energy Malnutrition is a deficiency of
both protein and energy
– Kwashiorkor -- a form of PEM that results
either from inadequate protein intake or, more
commonly, from infections
• Is the Ghanaian name for “the evil sprit that infects
the first child when the second child is born”
• Theory -- May be a form of food poisoning
superimposed on malnutrition
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PROTEIN
HEALTH EFFECTS OF PROTEIN
• Protein Energy Malnutrition (PEM)
– Kwashiorkor (continued)
• Symptoms
– Growth slows
– Hair looses color
– Skin becomes patchy and scaly (sometimes with ulcers
and sores that fail to heal)
– Limbs and face become swollen with edema (protein in
the blood becomes depleted and water cannot be held
there, instead it seeps into interstitial space and
accumulates)
– Belly bulges with fatty liver
– Sickens easily, becomes weak, fretful, and apathetic
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PROTEIN
HEALTH EFFECTS OF PROTEIN
• Protein Energy Malnutrition (PEM)
– Kwashiorkor (continued)
• Occurs on every continent
• Typically sets in at the age of two
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PROTEIN
HEALTH EFFECTS OF PROTEIN
• Protein Energy Malnutrition (PEM)
– Kwashiorkor (continued)
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PROTEIN
HEALTH EFFECTS OF PROTEIN
• Protein Energy Malnutrition (PEM)
– Kwashiorkor (continued)
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PROTEIN
HEALTH EFFECTS OF PROTEIN
• Protein Energy Malnutrition (PEM)
– Marasmus -- the disease of starvation
•
•
•
•
•
•
•
Occurs in persons who receive little of no food
Marasmic child looks like “skin and “bones”
Often sick because resistance to disease is low
Muscles are wasted, including the heart
Little or no fat to insulate against the cold
Occurs most commonly in children 6-18 months old
Impairs brain development
– Brain normally grows to adult size by 2 years of life
– May have permanent effect on learning ability
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PROTEIN
HEALTH EFFECTS OF PROTEIN
• Protein Energy Malnutrition (PEM)
– Marasmus
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PROTEIN
HEALTH EFFECTS OF PROTEIN
• Protein Energy Malnutrition (PEM)
– Marasmus
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PROTEIN
HEALTH EFFECTS OF PROTEIN
Body’s Priority System (Protein Priority System)
1. Abandons less vital systems first (hair and
pigments which are made of amino acids)
are the first to go
2. Antibodies are degraded so their amino
acids can be used as building blocks for the
heart, lungs, and brain tissues
3. Resistance to infection is therefore lowered
4. Malnutrition and infection are a deadly
combination
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PROTEIN
HEALTH EFFECTS OF PROTEIN
• Protein Excess
– No Benefits
• Excess NH2 must be excreted causing kidneys to
work harder
• Excess amino acids are stored as fat
– Risks
• Obesity -- protein-rich foods are often high fat foods
• The more protein consumed, the more likely fruits
and vegetables will be crowded out of the diet,
making in inadequate in other nutrients
• Studies suggest diets high in protein promote
calcium excretion
*****
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PROTEIN
RECOMMENDED PROTEIN INTAKES
• Body Losses
– Skin cells flake off or are rubbed off every day
– Hair and nails grow longer and are shed or cut
away
– People need to replace losses
• If the body is growing, the needs are greater
than just for maintenance
****
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PROTEIN
RECOMMENDED PROTEIN
INTAKES
• Nitrogen Balance -- the amount of
nitrogen consumed (N in) as
compared with the amount of
nitrogen excreted (N out)
– If the body maintains in its tissues the
same amount of protein from day to
day it is in nitrogen balance
– If the body looses protein it is in
negative nitrogen balance
•
•
•
•
Fasting
Starvation
Illness
Burn victims (forced to use protein for
energy)
***
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PROTEIN
RECOMMENDED PROTEIN INTAKES
• If the body gains protein it is in positive
nitrogen balance
• Growing children
• Pregnant women
**
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PROTEIN
RECOMMENDED PROTEIN INTAKES
DIETARY REFERENCE INTAKE VALUE
• AI
– Males over 18 -- 56 grams
– Females over 18 -- 46 grams
• RDA
– Healthy adults over 18 need 0.8 grams of high
quality protein per kilogram of appropriate or
average body weight for height
2002 Data
*
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PROTEIN
RECOMMENDED PROTEIN INTAKES
• Assumptions
• Protein eaten will be of high quality
• It will be consumed with adequate energy from
carbohydrate and fat
• Other nutrients in the diet will be adequate
• Individual is healthy and there is no unusual
metabolic need for protein
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