Transcript Proteins - Biol1322

Chapter 5
The
Proteins
and Amino
Acids
© 2007 Thomson - Wadsworth
Ask Yourself
1. Protein eaten in excess of need is stored
intact in the body, as is fat, so that it can be
used when a person’s diet falls short of
supplying the day’s need for essential
proteins.
2. No new living tissue can be built without
protein.
3. Whenever cells are lost, protein is lost.
4. All enzymes and hormones are made of
protein.
5. When antibodies enter the body, they produce
illness.
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Ask Yourself
6. When a person doesn’t eat enough food to
meet the body’s energy needs, the body
devours its own protein tissue.
7. Once the body has assembled its proteins into
body structures, it never lets go of them.
8. Milk protein is the standard against which the
quality of other proteins is usually measured.
9. It is impossible to consume too much protein.
10. People who eat no meat have to eat a lot of
special foods to get enough protein.
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What Proteins Are Made Of
• Proteins: compounds—
composed of atoms of
carbon, hydrogen, oxygen,
and nitrogen—arranged as
strands of amino acids.
Some amino acids also
contain atoms of sulfur.
 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.
 Amine (a-MEEN): group the
nitrogen-containing portion of
an amino acid.
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What Proteins Are Made Of
• Nine essential amino
acids:









Histidine
Isoleucine
Leucine
Lysine
Methionine
Phenylalanine
Threonine
Tryptophan
Valine
• 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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What Proteins Are Made Of
• Protein synthesis:
the process by which cells
assemble amino acids
into proteins.
 Each individual is unique
because of minute
differences in the ways his
or her body proteins are
made.
 The instructions for making
every protein in a person’s
body are transmitted in the
genetic information the
person receives at
conception.
• Peptide bond: a bond
that connects one amino
acid with another.
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What Proteins Are Made Of
• Proteins are made of many different
amino acid units hooked to each other.
 Strands of proteins are tangled chains,
globular in structure.
• The differing shapes of proteins enable
them to perform different tasks in the
body.
 Proteins may repel or attract water.
 Some proteins contain minerals or vitamins.
 Several proteins may gather to form a
functional group.
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What Proteins Are Made Of
• Denaturation: the
change in shape of a
protein brought about 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 cleave
peptide bonds.
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Cooking an egg
denatures its
proteins.
Functions of Body Proteins
• No living tissue can be built
without protein.
• Protein is part of every living cell.
• Proteins account for about 20% of
our body weight.
• Proteins come in many forms and
perform many vital functions.
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© 2007 Thomson - Wadsworth
Functions of Body Proteins
• Amino acids are constantly needed for the
body to build the proteins of new tissue
during growth and maintenance.
 Examples of growth: a developing embryo; a
growing child.
 Examples of maintenance: replacing blood lost
to burns, hemorrhage, or surgery; developing
scar tissue that heals wounds; replacing hair
or nails; replacing cells that are worn out.
• Amino acids must constantly be resupplied
by food for new growth to occur.
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Functions of Body Proteins
• Proteins form vital parts of most of
our body structures.
Examples of body structures include
skin, hair, nails, membranes,
muscles, teeth, bones, organs,
ligaments and tendons.
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Functions of Body Proteins
• Enzyme Action
Each enzyme
facilitates a specific
chemical reaction.
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Functions of Body Proteins
• Hormones: chemical messengers.
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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Functions of Body Proteins
• 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).
 Antibodies inactivate the foreign substances and so
protect the body.
• The foreign substances are called antigens.
• Immunity: specific disease resistance
derived from the immune system’s memory of
prior exposure to specific disease agents and
its ability to mount a swift response against
them.
 Malnutrition injures the immune system.
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An optimal diet
helps to provide
strength and
support to the
body’s immune
system.
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Functions of Body Proteins
• Fluid balance:
distribution of
fluid among body
compartments.
• Shown here are
the fluids within
and surrounding a
cell. Body
proteins help hold
fluid within cells,
tissues, and blood
vessels.
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Functions of Body Proteins
• Acid-Base Balance: equilibrium between
acid and base concentrations in the body
fluids.
 Acid-base balance of blood is carefully
controlled.
• Normal body processes continually
produce acids and bases.
Acids: compounds that release hydrogens in
a watery solution; acids have a low pH.
Bases: compounds that accept hydrogens
from solutions; bases have a high pH.
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pH Values of Selected Fluids
A fluid’s acidity or alkalinity is
measured in pH units.
pH: the concentration of
hydrogen ions. The lower the
pH, the stronger the acid
•pH 2 is a strong acid,
•pH 7 is neutral, and
•pH above 7 is alkaline.
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Functions of Body Proteins
Acid-Base Balance
• Acidosis (a-sih-DOSE-sis): blood acidity
above normal, indicating excess acid.
• Alkalosis (al-kah-LOH-sis): blood
alkalinity above normal.
• Buffers: compounds that help keep a
solution’s acidity (amount of acid) or
alkalinity (amount of base) constant.
 Some proteins act as buffers to maintain
normal blood pH.
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Functions of Body Proteins
Transport Proteins specialize in
moving nutrients and molecules
into and out of cells.
The “sodium-potassium pump” is
switched on and off by hormones.
Special proteins carry vitamins,
minerals.
Lipoproteins carry lipids.
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Functions of Body Proteins
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.
Urea (yoo-REE-uh): the principal nitrogen
excretion product of metabolism, generated
mostly by the removal of amine groups from
unneeded amino acids or from those amino
acids being sacrificed to a need for energy.
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Functions of Body Proteins
Protein As Energy:
• After the amine group is removed, the
remaining carbon, hydrogen and oxygen
will be used for immediate energy.
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.
• Excess amino acids are not stored by the
body.
 After removing the amine group, the excess is
converted to glycogen or fat for energy storage.
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© 2007 Thomson - Wadsworth
How the Body Handles Protein
• By the time proteins slip
into the small intestine,
they are already broken
into different-sized
pieces.
 Some single amino acids
and many strands of two,
three, or more amino
acids.
 There are dipeptides,
tripeptides, and longer
chains.
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How the Body Handles Protein
• Amino acids pass from the absorptive
cells in the small intestine into the
bloodstream, where they can be taken
up by cells and used to make proteins.
• Amino acid strands are assembled to
make proteins.
 Nonessential amino acids can be
manufactured by the body from fragments
of other amino acids.
 If essential amino acids are missing,
protein building will halt.
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Protein Quality of Foods
• Important characteristics of dietary
protein:
 Should supply at least the essential amino
acids.
 Should supply enough other amino acids to
make nitrogen available for synthesizing
other nonessential amino acids.
 Should provide adequate food energy to
prevent sacrifice of amino acids for energy.
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Protein Quality of Foods
• Complete proteins: proteins containing all
the essential amino acids in the right proportion
relative to need. The quality of a food protein is
judged by the proportions of essential amino
acids that it contains relative to our needs.
Animal proteins are the highest in quality.
• Incomplete protein: a protein lacking or
low in one or more of the essential amino acids.
• Limiting amino acid: a term given to the
essential amino acid in shortest supply (relative
to the body’s need) in a food protein; it
therefore limits the body’s ability to make its
own proteins.
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Protein Quality of Foods
• Protein quality: a measure of the
essential amino acid content of a protein
relative to the essential amino acid needs of
the body.
• Biological value (BV): a measure of
protein quality, assessed by determining how
well a given food or food mixture supports
nitrogen retention.
• Reference protein: egg white protein, the
standard with which other proteins are
compared to determine protein quality.
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Protein Quality of Foods
• Complementary
proteins: two or
more food proteins
whose amino acid
assortments
complement each
other in such a way
that the essential
amino acids limited
in or missing from
each are supplied by
the others.
Both meals shown supply an
adequate assortment of
amino acids
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Protein Quality of Foods
HOW TWO PLANT PROTEINS
COMBINE TO YIELD A COMPLETE
PROTEIN:
• Two incomplete proteins (for
example, legumes plus grains)
can be combined to equal a
complete protein (peanut
butter sandwich). In this
example,
 the peanut butter provides adequate
amounts of the amino acid lysine, but
is lacking in methionine.
 The bread “complements” the peanut
butter because it contains adequate
methionine, but is lacking in lysine.
• When combined as a sandwich,
all essential amino acids are
present.
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Recommended Protein
Intakes
• Recommended protein intakes can
be stated by two methods.
As a percentage of total calories:
• Protein should provide 10-35% of total
calories.
As an absolute number (grams per
day).
• A healthy adult should consume 0.8 gram
per kilogram of desirable body weight per
day.
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Recommended Protein
Intakes
To calculate the percentage of calories you
derive from protein:
1. Use your total calories as the denominator
(example: 1,900 cal).
2. Multiply your total protein intake in grams by
4 cal/g to obtain calories from protein as the
numerator (example: 70 g protein X 4 cal/g
= 280 cal).
3. Divide to obtain a decimal, multiply by 100,
and round off (example: 280/1,900 X 100 =
15% cal from protein).
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Recommended Protein
Intakes
To figure your recommended protein intake
(RDA):
1.
2.
3.
Find the desirable weight for a person your height
(see Appendix B). Assume this weight is appropriate
for you.
Change pounds to kilograms (divide pounds by 2.2;
one kilogram = 2.2 pounds).
Multiply kilograms by 0.8 g/kg.

Example (for a 5’8” male):
1. Desirable weight: about 150 lb.
2. 150 lb. divide by 2.2 lb. = 68 kg (rounded off).
3. 68 kg X 0.8 g/kg = 54 g protein (rounded off).
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Protein and Health
• Protein deficiency and energy deficiency
go hand in hand so often that public
health officials have given a nickname
to the pair.
Protein-energy malnutrition
(PEM), also called protein-calorie
malnutrition (PCM): the world’s
most widespread malnutrition
problem, including both kwashiorkor
and marasmus.
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Protein and Health
• Kwashiorkor (kwashee-OR-core): a
deficiency disease caused
by inadequate protein in
the presence of adequate
food energy.
• Edema (eh-DEEM-uh):
swelling of body tissue
caused by leakage of fluid
from the blood vessels,
seen in (among other
conditions) protein
deficiency.
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Protein and Health
• Marasmus (ma-RAZ-
mus): an energy deficiency
disease; starvation.
• Dysentery (DISS-enterry): an infection of the
digestive tract that causes
diarrhea.
• Acquired immune
deficiency syndrome
(AIDS): an immune system
disorder caused by the
human immunodeficiency
virus (HIV).
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Protein and Health
Too Much Protein
• 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.
 No apparent benefit to consuming too much
protein when caloric intake is adequate.
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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
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Protein and Health
• The average protein consumption in the
United States is 67.5 grams of protein per day
or about 15% of total caloric intake, of which:
 37 grams (55%) come from the Meat &
Beans Group.
 The Milk and Grains Groups are the next
two largest contributors, providing 36% of
the total daily protein.
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1. Enjoy adding
more legumes to
your weekly
meals.
2. Enjoy a variety
of dried, beans,
peas, and lentils
when dining out.
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Protein and Health
• Legumes (leg-GYOOMS):
plants of the bean and pea family
having roots with nodules that
contain bacteria that can trap
nitrogen from the air in the soil
and make it into compounds that
become part of the seed.
The seeds are rich in high-quality
protein compared with those of most
other plant foods.
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The New American Plate:
• In the Kitchen:
 Small meat portions tend to
work best mixed into dishes
with lots of vegetables and
grains…
• In the Lunch Box:
 Take a thermos filled with
chili, vegetable soup, or a
milk-based soup, such as
cream of tomato, prepared
with nonfat milk instead of
a sandwich…
• At the Table:
 Make whole grains,
vegetables, and legumes
the main event of your
meals…
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The Vegetarian Diet
• Well-planned, plantbased meals consisting
of:
 A variety of whole
grains
 Legumes and nuts
 Vegetables and fruits
 Eggs and dairy
products (for some
vegetarians)
• Can offer sound nutrition
and health benefits to
vegetarians and nonvegetarians alike
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© 2007 Thomson - Wadsworth
The Vegetarian Diet
• Nutritional yeast: a fortified food
supplement containing B vitamins, iron,
and protein that can be used to improve
the quality of a vegetarian diet.
• Meat replacements: textured
vegetable protein products formulated
to look and taste like meat, fish, or
poultry.
Many of these are designed to match
the known nutrient contents of
animal protein foods.
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© 2007 Thomson - Wadsworth
Food Allergy—Nothing to Sneeze At
• Food aversion: a strong desire to avoid a particular
food.
• Food allergy: an adverse reaction to an otherwise
harmless substance that involves the body’s immune
system.
• Food intolerance: a general term for any adverse
reaction to a food or food component that does not
involve the body’s immune system.
• Adverse reaction: an unusual response to food,
including food allergies and food intolerances.
• Food allergen: a substance in food— usually a
protein—that is seen by the body as harmful and causes
the immune system to mount an allergic reaction.
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Food Allergy—Nothing to
Sneeze At
• Histamine: a substance released by cells of the
immune system during an allergic reaction to an antigen,
causing inflammation, itching, hives, dilation of blood
vessels, and a drop in blood pressure.
• Anaphylaxis (an-ah-fa-LAX-is): a potentially fatal
reaction to a food allergen causing reduced oxygen supply to
the heart and other tissues.
 Symptoms include:
• difficulty breathing
• low blood pressure
• pale skin
• a weak, rapid pulse
• loss of consciousness
• Cross-reaction: the reaction of one antigen with
antibodies developed against another antigen.
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Common sites of
allergic reactions
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The top eight foods causing adverse reactions
in some individuals: milk, eggs, peanuts, nuts,
fish, shellfish, soy, and wheat (pictured above)
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© 2007 Thomson - Wadsworth
© 2007 Thomson - Wadsworth
© 2007 Thomson - Wadsworth
Wonder Bean: The Benefits of Soy
• The new information
about soy seems
promising.
• Science has not yet
established a
recommended daily
amount of soy to be
consumed.
 In many cases, just one
serving of soy per day
may help improve your
health.
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