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Chapter 6: Proteins and
Amino Acids
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What Are Proteins?
Large molecules
Made up of chains of amino acids
Are found in every cell in the body
Are involved in most of the bodys functions and lifeprocesses
The sequence of amino acids is determined by DNA
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Structure of Proteins
Made up of chains of amino acids; classified by number of
amino acids in a chain Peptides: fewer than 50 amino acids
- Dipeptides: 2 amino acids
- Tripeptides: 3 amino acids
- Polypeptides: more than 10 amino acids
Proteins: more than 50 amino acids
- Typically 100 to 10,000 amino acids linked together
Chains are synthesizes based on specific bodily DNA Amino acids are composed of carbon, hydrogen, oxygen,
and nitrogen
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Structural Differences Between Carbohydrates,Lipids, and Proteins
Figure 6.1
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The Anatomy of an Amino Acid
Figure 6.2b
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Peptide Bonds Link Amino Acids
Form when the acid group (COOH) of one amino acid joins
with the amine group (NH2) of a second amino acid Formed through condensation
Broken through hydrolysis
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Condensation and Hydrolytic Reactions
Figure 6.3
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Structure of the Protein
Four levels of structure
Primary structure Secondary structure
Tertiary structure
Quaternary structure
Any alteration in the structure or sequencing changes
the shape and function of the protein
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Denaturing
Alteration of the proteins shape and thus functions
through the use of Heat
Acids
Bases
Salts
Mechanical agitation
Primary structure is unchanged by denaturing
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Denaturing a Protein
Figure 6.5
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Quick Review
Proteins are chains of combination of amino acids
Amino acids contain carbon, hydrogen, oxygen, nitrogen,and sometimes sulfur
Unique amino acids consist of a central carbon with acarboxyl group, a hydrogen, a nitrogen-containing amine
group, and a unique side chain There are 20 side chains and 20 unique amino acids
9 essential amino acids
11 nonessential amino acids- At time these become conditionally essential
Amino acids link together with peptide bonds bycondensation and break apart by hydrolysis
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Quick Review
Attractions and interactions between the side chains cause
the proteins to fold into precise three-dimensional shapes Protein shape determines its function
Proteins are denatured and their shapes changed by
Heat
Acids
Bases
Salts
Mechanical agitation
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Protein Digestion: Part 1
Figure 6.6
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Protein Digestion: Part 2
Figure 6.6
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Protein Digestion: Part 3
Figure 6.6
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Protein Digestion: Part 4
Figure 6.6
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Amino Acid Absorption
Amino acids are absorbed in the small intestine
Amino acids are transported to the liver from the intestinesvia the portal vein
In the liver, amino acids are
Used to synthesize new proteins
Converted to energy, glucose, or fat
Released to the bloodstream and transported to cellsthroughout the body
Occasionally proteins are absorbed intact
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Amino Acid Metabolism
Liver metabolizes amino acids, depending on bodily needs
Most amino acids are sent into the blood to be picked upand used by the cells
Amino acid pool is limited but has many uses
Protein turnover the continual degradation and
synthesizing of protein
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Deamination
When the amino acid pool reaches capacity the amino acids
are broken down to their component parts for other uses First deamination must occur
Carbon-containing remnants are
Converted to glucose, if they are glucogenic amino acids,
through gluconeogensis
Converted to fatty acids and stored as triglycerides inadipose tissue
M b li F f A i A id
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Metabolic Fate of Amino Acids
Figure 6.7
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Quick Review
During digestion
Proteins are broken down to amino acids with the help of- Gastric juices
- Enzymes in the stomach and small intestine
- Enzymes from the pancreas and small intestine lining
Limited supply of amino acids exist in the amino acid pool The amino acid pool acts as a reservoir for protein
synthesis
Surplus amino acids are
Deaminated- Used for glucose or energy
- Stored as fat
- Nitrogen is converted to urea and excreted in urine
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How Does the Body Use Protein?
Functions of protein
Provide structural and mechanical support Maintain body tissues
Functions as enzymes and hormones
Help maintain acid base balance
Transport nutrients
Assist the immune system
Serve as a source of energy when necessary
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Quick Review
Protein plays many important roles in the body, including:
Helping facilitate muscular contraction Promoting satiety and appetite control
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How Much Protein Do You Need?
Healthy, nonpregnant adults
Should consume enough to replace what is used everyday
The goal is nitrogen balance
Pregnant woman, people recovering from surgery or injury,
and growing children
Should consume enough to build new tissue
Nit B l d I b l
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Nitrogen Balance and Imbalance
Figure 6.12
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Not All Protein Is Created Equal
High quality protein
Is digestible Contains all essential amino acids
Provides sufficient protein to synthesize nonessentialamino acids
It helps to be aware of:
Amino acid score
Limiting protein
Protein digestibility corrected amino acid score(PDCAAS)
Biological value of protein rates absorption and retentionof protein for use
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Protein Quality
Complete proteins
Contain all nine essential amino acids Usually animal source are complete proteins
Are considered higher quality
Incomplete proteins
Low in one or more essential amino acid
Usually plant sources are incomplete
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Protein Needs
Protein intake recommendations
1035% of total daily kilocalories Adults over 18
- 0.8 g/kg daily
American College of Sports Medicine, the AmericanDietetic Association, and other experts advocate
50100% more protein for competitive athletesparticipating in endurance exercise or resistance exercise
Typically this population eats more and therefore getsadditional protein
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Quick Review
Protein quality is determined by digestibility and types and
amounts of amino acids Animal protein is more easily digested and complete
Plant proteins are typically incomplete, except soy
Plant proteins can be complemented with proteins from
other plant sources or animal source to improve theirquality
Adults should consume 0.8 g/kg/d of protein
Men and women in the United States tend to over consume
protein
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Best Sources of Protein
Proteins are abundant in
Dairy foods Meats
Poultry
Meat alternatives such as dried beans, peanut butter,nuts, and soy
3 oz serving of cooked meat, poultry, or fish
Provides 2125 grams of protein
About 7 g/oz About the size of a deck of cards
Adequate amount for one meal
Best Sources of Protein
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Best Sources of Protein
Figure 6.14
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Quick Review
A well-balanced diet can meet daily protein needs
Best source of protein are animal products Eggs
Lean meats
Low-fat or fat-free dairy products
Plant proteins such as soy, grains, and vegetables supplysubstantial proteins
Most people consume adequate protein from their diet anddo not need protein supplements
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Protein Bars
Are marketed as convenient and portable
Can be High in saturated fat and/or sugar
Low in fiber
Expensive
A peanut butter sandwich is portable and lower in saturatedfat and sugar and higher in fiber than some protein bars
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Eating Too Much Protein
Risk of heart disease
Risk of kidney stones Risk of calcium loss from bones
Risk of colon cancer
Displacement of other nutrient-rich, disease preventingfoods
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Types of PEM: Kwashiorkor
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Types of PEM: Kwashiorkor
Severe protein deficiency
Generally result of a diet high in
grains and deficient in protein Symptoms range from
Edema in legs, feet, and stomach
Muscle tone and strength
diminish Hair is brittle and easy to pull out
Appear pale, sad, and apathetic
Prone to infection, rapid heartrate, excess fluid in lungs,
pneumonia, septicemia, andwater and electrolyte imbalances(Image from http://www.thachers.org/pediatrics.htm)
Figure 6.16
Types of PEM: Marasmus
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Types of PEM: Marasmus
Results from a severe deficiencyin kilocalories
Frail, emaciated appearance Weakened and appear apathetic
Many cannot stand withoutsupport
Look old
Hair is thin, dry, andlackssheen
Body temperature and blood
pressure are low
Prone to dehydration,infections, and unnecessary
blood clotting
Figure 6.17
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Treatment for PEM
Medical and nutritional treatment can dramatically reduce
mortality rate Should be carefully and slowly implemented
Step 1 Address life-threatening factors
- Severe dehydration
- Fluid and nutrient imbalances
Step 2 Restore depleted tissue
- Gradually provide nutritionally dense kilocalories andhigh-quality protein
Step 3 Transition to foods and introduce physicalactivity
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Vegetarian Diet
People choose vegetarian diets for a variety of reasons
Ethical Religious
Environmental
Health
Vegetarians must consume adequate amounts of a varietyof food and should plan meals well
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P i l B fi Ri k f V i Di
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- Cancer
- Stroke
- Obesity
Potential Benefits, Risks of a Vegetarian Diet
Benefits of a healthy vegetarian diet
Reduced risk of- Heart disease
- High blood pressure
- Diabetes
Potential risks of a vegetarian diet
Underconsumption of certain nutrients
- Protein- Vitamin B12
Vegetarian Food Guide Pyramid
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Vegetarian Food Guide Pyramid
Figure 6.18
S
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Soy
Soy is increasing in popularity in the United States
High-quality protein source Low in saturated fat
Contains isoflavones
Phytoestrogens
May reduce risk of heart disease
Some research suggests it may reduce the risk of cancer
Some concern it may promote breast cancer
Q i k R i
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Riboflavin
Vitamin B12
Vitamin A
Omega-3 fatty acids
Quick Review
Vegetarian diets can be a healthy eating style that may help
reduce the risk of some chronic disease Some vegetarians abstain from all animal products
Some vegetarians eat eggs and dairy in limited amounts
Vegetarians must plan their diets carefully to meet their
nutrient needs, especially Protein
Iron
Zinc
Calcium
Vitamin D
P tti It All T th
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Putting It All Together
Majority of daily kilocalories should come from
carbohydrate-rich foods Fat intake should be no more than about one-third of daily
kilocalories
Protein should provide the rest of the daily kilocalories
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Putting It All Together
Best plan for a healthful diet
Eat an abundance of- Grains (at least whole grains)
- Vegetables
- Fruits
Eat modest amounts of- Commercially made bakery and snack items
- Vegetables with creamy sauces or added butter
- Sweets
Choose low-fat dairy products, lean meat, poultry, andfish to minimize the intake of heart-unhealthy saturatedfats