Transcript Proteins - HCC Learning Web

Chapter 6
Protein and Amino
Acids
Sources of Protein in the Diet
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Protein deficiency is rare in the United
States.
In the US, about two-thirds of dietary protein
comes from meat, poultry, seafood, eggs
and dairy products.
Most of the world relies on plant proteins
from grains and vegetables.
As a country’s economy improves, the
proportion of animal foods in the diet tends
to increase.
Copyright 2010, John Wiley & Sons, Inc.
Sources of Protein in the Diet
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Sources of Protein in the Diet
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Animal versus Plant Protein
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Animal products provide sources of protein,
B vitamins and minerals such as iron, zinc
and calcium.
However, animal products are low in fiber
and can be high in fat.
Plant sources of protein are also a good
source of B vitamins, iron, zinc, fiber and
calcium, but in less absorbable forms.
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Amino Acids
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Amino acids are the building blocks of
protein.
Each amino acid contains a central carbon
atom bound to a hydrogen atom, an amino
group, an acid group and a side chain.
Essential amino acids cannot be
synthesized by the human body in sufficient
amounts to meet needs.
Essential amino acids must be included in
the diet.
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Amino Acids and Protein Structure
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Proteins: atoms of carbon, hydrogen, oxygen,
and nitrogen—arranged as strands of amino
acids.
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Amino (a-MEEN-o) acids: building blocks of
protein; each is a compound with an amine
group at one end, an acid group at the other,
and a distinctive side chain.
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Amine (a-MEEN): group the nitrogencontaining portion of an amino acid.
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Amino Acids and Protein Structure
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Amino Acids and Protein Structure
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Nine essential amino
acids:
 Histidine
 Isoleucine
 Leucine
 Lysine
 Methionine
 Phenylalanine
 Threonine
 Tryptophan
 Valine
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Essential amino
acids: amino acids that
cannot be synthesized by
the body or that cannot
be synthesized in
amounts sufficient to
meet physiological need.
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Amino Acids and Protein Structure
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Proteins are made of many different amino
acid units hooked to each other.
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A strand of protein is not straight; it is
more like a tangled chain. The amino
acids at different places along the stand
are attracted to one another, and this
attraction causes the strand to coil into a
shape similar to that of a metal spring.
This coil tangle has a globular structure.
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Amino Acids and Protein Structure
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The differing shapes of proteins enable them to
perform different tasks in the body.
 Proteins may repel or attract water. (Charged
amino acids are attracted to water, the neutral
amino acids are repelled by water)
 Some proteins contain minerals or vitamins.
 Several proteins may gather to form a
functional group.
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Amino Acids and Protein Structure
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Phenylketonuria
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Amino Acids and Protein Structure
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Denaturation: the change in shape of
a protein by heat, alcohol, acids,
bases, salts of heavy metals, or other
agents.
 First step in the protein’s breakdown.
 Useful to the body in digestion.
 Stomach acid opens up the protein’s
structure, allowing digestive
enzymes to spilt peptide bonds.
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Amino Acids and Protein Structure
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Cooking an egg
denatures its proteins.
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Cooking eggs liberates
biotin and iron and helps
in protein digestion
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Protein Digestion and Absorption
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When a food protein is eaten, the digestive system
breaks the protein down and delivers the separated
amino acids to the body cells that put the amino acids
together in the order necessary to produce needed
proteins.
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Protein digestion
 Initiated in the stomach
 Moves into the small intestine as single amino acids,
or strands of two, three, or more amino acids.
 Digestion continues until almost all pieces of protein
are broken into dipeptides, tripeptides, and more free
amino acids.
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Protein Digestion and Absorption
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By the time proteins slip into the
small intestine, they are already
broken into different-sized pieces.
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Some single amino acids and
many strands of two, three, or
more amino acids.
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There are dipeptides,
tripeptides, and longer chains.
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Protein Digestion and Absorption
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Protein absorption
 Absorption of amino acids takes place all along the
small intestine.
 The cells that line the small intestine capture
dipeptides and tripeptides on their surface, split
them into amino acids on the cell surfaces,
absorb them, and then release them into the
blood stream.
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Amino acids are available to be taken up by any
cell when they are circulating in the bloodstream.
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The cells can then make proteins for their own use.
© 2007 Thomson - Wadsworth
Protein Digestion and Absorption
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Nonessential amino acids can be
manufactured by the body from
fragments of other amino acids.
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If essential amino acids are missing,
protein building will halt.
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Protein Digestion and Absorption
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Nonessential versus essential amino acids
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Cells make protein strands from nonessential amino
acids.
If essential amino acids are missing in the cell, the
cells cannot complete the protein strand, and so
protein building stops.
The cell cannot hold these partially completed
proteins; therefore, they are dismantled and return into
circulation, making them available to other cells.
If other cells do not soon pick up these amino acids
and insert them into proteins, the liver will remove their
amine groups for the kidney to excrete.
© 2007 Thomson - Wadsworth
Protein
Digestion
and
Absorption
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Synthesizing Protein
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Synthesizing Protein
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Synthesizing Protein
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Synthesizing Protein
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Function of Protein in the Body
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Protein is part of every living cell.
No living tissue can be built without protein.
Proteins account for about 20% of our body
weight.
Proteins come in many forms and perform
many vital functions (enzymes, antibodies, hormones,
transport vehicles, oxygen carriers, tendons and ligaments, scars,
the cores of bones and teeth, the filaments of hair, materials of
nails).
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Function of Protein in the Body
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Growth and maintenance
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Regulatory rules
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Building materials for growth and maintenance
Body structure
Enzyme
Hormones
Antibodies
Fluid balance
Acid-base balance
Transportation
Energy Production
Function of Protein in the Body
•All enzymes are proteins,
and are among the most
important proteins
because they are
catalysts that help
chemical reactions take
place (Biological spark
plug).
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Enzyme Action
Each enzyme facilitates
a specific chemical
reaction.
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Function of Protein in the Body
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Hormones:
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Hormones are similar to enzymes in the importance
of their function,
they differ
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Not all are made of protein,
They do not catalyze chemical reactions directly
Instead act as messengers that maintain a normal
environment within the body.
chemical messengers.
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Hormones are secreted by a variety of glands in the
body in response to altered conditions.
Each affects one or more target tissues or organs and
elicits specific responses to restore normal conditions.
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Function of Protein in the Body
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Antibodies: large proteins of the blood and body
fluids, produced by one type of immune cell in
response to invasion of the body by unfamiliar
molecules (mostly foreign proteins).
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Antibodies inactivate the foreign substances and so protect
the body.
Each antibody is uniquely designed to destroy a specific
foreign antigen.
 The foreign substances are called antigens.
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One the body learn to make a particular antibody it
never forgets and next time even it destroy the
antigen even more rapidly (Immunity).
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Malnutrition injures the immune system.
Often protein deficiency and immune incompetence appear
together.
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Function of Protein in the Body
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Fluid balance
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Proteins help regulate the quantity of fluids in cell
compartments to maintain fluid balance – necessary
for life.
Too much, it ruptures.
Too little, it is unable to function.
Proteins attract water
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Proteins cannot diffuse freely in and out of cells
The water-attracting protein stores inside the cells help the
cells meet their fluid needs.
Proteins released into the blood (blood vessels)
act in the same way in maintaining blood volume.
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Function of Protein in the Body
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Function of Protein in the Body
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Protein as a Source of Energy
Protein As Energy:
 In the absence of adequate energy,
the body will sacrifice protein to
provide energy.
 The amine group will be degraded,
incorporated by the liver into urea,
and sent to the kidneys for excretion
in urine.
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Protein as a Source of Energy
Protein As Energy:
 After the amine group is removed, the remaining
carbon, hydrogen and oxygen will be used for
immediate energy.
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Protein sparing: a description of the effect of
carbohydrate and fat, which, by being available to yield
energy, allow amino acids to be used to build body
proteins.
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Excess amino acids are not stored by the body.
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After removing the amine group, the excess is
converted to glycogen or fat for energy storage.
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Protein as a Source of Energy
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Protein Deficiency
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Protein-energy malnutrition (PEM) is a term
that covers a range of protein deficiency
conditions that may include only protein
deficiency or protein deficiency plus energy
deficiency.
Kwashiorkor is a pure protein deficiency.
Marasmus is an energy deficiency.
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Protein Deficiency
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Kwashiorkor (the evil spirit that
infects the first child when the second
child is born ): a deficiency disease
caused by inadequate protein in the
presence of adequate food energy.
Symptoms
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Edema : swelling of body tissue caused
by leakage of fluid from the blood
vessels, seen in (among other
conditions) protein deficiency.
Apathy: no cry even for foods.
Skin and hair: Changes in skin pigment
and hair color and texture (no protein
pigment)
Fatty liver: (Lack of lipoproteins)
Failure to gain weight and grow
Loss of muscle mass
Anemia (Blood protein is not
synthesis including hemoglobin)
Protein Deficiency
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Marasmus (ma-RAZ-mus): an energy
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deficiency disease; starvation.
Symptoms: Same as kwashiorkor
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Differences: Wizened little old person, just
bone and skin
Dysentery (DISS-en-terry): an
infection of the digestive tract that
causes diarrhea..
Metabolism is slow so the temperature
is subnormal.
Acquired immune deficiency
syndrome (AIDS): an immune
system disorder caused by the human
immunodeficiency virus (HIV).
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Protein Deficiency
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Treatment:
 Getting more calories and protein will
correct kwashiorkor, if treatment is started
early enough. However, children who have
had this condition will never reach their full
height and growth.
Prevention
 To prevent kwashiorkor, diet must have
enough carbohydrates, fat, and protein.
© 2007 Thomson - Wadsworth
Protein Deficiency
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In general PEM cases:
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Epidemiology: prevalent in Africa, Central
America, South America, and Asia.
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Cases are targeted easily by any infections
(antibodies degraded to provide amino acids for other
uses)
Muscles are wasted, including heart muscles
Cases are reported in Indian reservations and in the
inner cities and impoverished rural areas of the
United States.
PEM is prevalent in unnourished patients
including:
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Those with anorexia nervosa, AIDS, cancer.
Protein Excess
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Elevated protein intakes over long periods
of time can results in:
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Hydration and kidney function issues
Bone health issues
Increased risk of heart disease and cancer
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Protein Excess
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The problems of protein excess can be found in developed
countries.
 Possible to overload the liver and kidneys.
 Can promote calcium excretion.
 Excess protein can be converted to energy and stored as
body fat.
 Excess protein may also create an increased demand for
vitamin B6 in the diet, so that the body can utilize the
protein.
 Since protein-rich foods are often high in saturated fat,
cholesterol, and calories, so can increase the risk of
obesity.
 The higher a person's intake of animal-protein sources, the
more likely to consume less fruits, vegetables, and grains,
so might other nutrient deficiency happen.
 No apparent benefit to consuming too much protein when
caloric intake is adequate.
© 2007 Thomson - Wadsworth
Protein and Health
Foods that supply protein in abundance are shown here in the
Milk Group and the Meat & Beans Group of the MyPyramid
Food Guide (top two photos).
Servings of foods from the Vegetable Group and the Grains
Group can also contribute protein to the diet (bottom two
photos).
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Protein
contributed by
food groups in the
average U.S. diet
© 2007 Thomson - Wadsworth
Protein Allergies
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Food allergies are triggered when a protein
from the diet is absorbed without being
completely digested.
Protein from milk, eggs, nuts, wheat, soy, fish
and shellfish and peanuts are common sources
of food allergies.
A rapid, severe allergic reaction is called
anaphylaxis.
People with GI disease are prone to allergies
because their damaged intestine allows for the
absorption of whole proteins.
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Food Allergy Labeling
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Meeting Protein Needs:
Nitrogen Balance
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General Protein Requirements
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Varying Protein Needs of Athletes
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Protein and Amino Acid Supplements
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Choosing
Protein
Wisely
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Types of Vegetarian Diets
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Nutrient Needs with a Vegan Diet
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Soy Protein
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What Should I Eat? Protein Sources
Get protein without too much saturated fat
• Plan on poultry or fish.
• Choose lean cuts of red meat.
• Grill, roast, or broil so that the fat will end up in the pan or the fire.
• Choose low-fat or reduced-fat milk.
Eat both animal and plant proteins
• Have your beef or chicken in a stir-fry with lots of vegetables.
• Serve a small portion of meat over noodles.
• Add nuts and seeds to snacks and salads.
• Have a meatless meal at least once a week.
Go with beans
• Try hummus—made from ground chickpeas and sesame seeds.
• Add kidney beans or chickpeas to soups.
• Snack on soy beans.
• Enjoy tacos or burritos stuffed with pinto beans or black beans.
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End of Chapter 6
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