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Proteins and Amino Acids

© 2010 Pearson Education, Inc
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Structure of Proteins
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Made up of chains of amino acids; classified by number of
amino acids in a chain
• Peptides: fewer than 50 amino acids
- Dipeptides: 3 amino acids
- Tripeptides: 4 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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The Anatomy of an Amino Acid

Figure 6
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Denaturing
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Alteration of the protein’s shape and thus functions
through the use of
• Heat
• Acids
• Bases
• Salts
• Mechanical agitation
Primary structure is unchanged by denaturing

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Protein Digestion: Part 4

Figure 6
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Amino Acid Metabolism
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Liver metabolizes amino acids, depending on bodily needs
Most amino acids are sent into the blood to be picked up
and 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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How Does the Body Use Protein?
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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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Protein Needs
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Protein intake recommendations
• 10–35% of total daily kilocalories
• Adults over 18
- 0
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Best Sources of Protein
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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 21–25 grams of protein
• About 7 g/oz
• About the size of a deck of cards
• Adequate amount for one meal

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Eating Too Much Protein
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Risk of heart disease
Risk of kidney stones
Risk of calcium loss from bones
Risk of colon cancer
Displacement of other nutrient-rich, disease preventing foods

Eating Too Little Protein
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Protein-energy malnutrition (PEM)
• Protein is used for energy rather than its other functions in the
body
• Other important nutrients are in short supply
• More prevalent in infants and children
- 17,000 children die each day as a result

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Types of PEM: Kwashiorkor
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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 heart
rate, excess fluid in lungs,
pneumonia, septicemia, and
water and electrolyte imbalances
(Image from http://www
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org/pediatrics
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Types of PEM: Marasmus
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Results from a severe deficiency
in kilocalories
• Frail, emaciated appearance
• Weakened and appear apathetic
• Many cannot stand without
support
• Look old
• Hair is thin, dry, and lacks
sheen
• Body temperature and blood
pressure are low
• Prone to dehydration,
infections, and unnecessary
blood clotting
Figure 6
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Treatment for PEM
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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 and
high-quality protein
• Step 3 – Transition to foods and introduce physical
activity

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Potential Benefits, Risks of a Vegetarian Diet
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Benefits of a healthy vegetarian diet
• Reduced risk of
- Cancer
- Heart disease
- Stroke
- High blood pressure
- Obesity
- Diabetes

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Potential risks of a vegetarian diet
• Underconsumption of certain nutrients
- Protein
- Vitamin B12

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Soy
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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

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Putting It All Together
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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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