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The Proteins and Amino
Acids
Chapter 6
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
Learning Objectives
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Describe why some amino acids are
essential, non-essential, or conditionally
essential to the human body, and state
the outcome should any one of them be
lacking from the diet.
Describe the digestion of protein and the
absorption and transport of amino acids in
the body.
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
Learning Objectives
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List the roles that various proteins and
amino acids can play in the body, and
describe the influence of carbohydrate on
amino acid metabolism.
Discuss the concept of nitrogen balance,
and compute the amount of protein
needed for a healthy college student.
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
Learning Objectives
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Discuss potential physical problems from
an eating plan that is too low or too high in
protein.
Identify protein-rich foods, and list some
extra advantages associated with
legumes.
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
Learning Objectives

Summarize the health advantages and
nutrition red flags of vegetarian diets, and
develop a lacto-ovo vegetarian eating
pattern that meets all nutrient
requirements for a given individual.
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
The Structure of Proteins
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Difference from carbohydrates and fats
Amino acids
Carbon atom with amine group and acid
group
 Side chain
 Essential amino acids
 Conditionally essential
 Recycling
 Priority system
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Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
Amino Acids Important in
Nutrition
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
How Do Amino Acids Build
Proteins?
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Peptide bonds
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Link amino acids
Strands of amino acids do not remain
straight
Coils
 Folds
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Side chain electrical charge
Activation
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
Different Amino Acids Join
Together
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
The Coiling and Folding of a
Protein Molecule
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
The Structure of Hemoglobin
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
The Variety of Proteins
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Protein shapes enable performance of
different tasks
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Protein strands – alone or in association
Inherited amino acid sequences
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Examples
Alterations to sequence
 Sickle-cell disease
Nutrients and gene expression
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
Normal Red Blood Cells and
Sickle Cells
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
Protein Synthesis
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
Denaturation of Proteins
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Denaturing agents
Digestion
 Stomach acid
 Cooking
 Salts of heavy
metals
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Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
Protein Digestion
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Stomach
Denatures protein in food
 Uncoil protein’s strands
 Enzymes attack peptide bonds
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Small intestine
Polypeptides
 Further break down
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Common misconceptions
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
A Dipeptide and Tripeptide
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
How Protein
in Food
Becomes
Amino
Acids in the
Body
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
Amino Acid Absorption
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Absorbed by cells of small intestine
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Separate sites for absorption
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Larger molecules
 Hormones or allergens
Types of amino acids
Released into the bloodstream
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Carried to the liver
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
The Importance of Protein
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Amino acids must
be continually
available
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Building of new
proteins
Amino acids are
needed each day
Protein turnover
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
The Roles of Body Proteins
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Regulation of gene expression
Providing structure and movement
Muscle tissue
 Other structural proteins
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Building enzymes
Building hormones
Other compounds
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Neurotransmitters
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
Enzyme Action
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
Amino Acid Sequence of Human
Insulin
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
The Roles of Body Proteins
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Building antibodies
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Transporting substances
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Destroy one specific invader
Hemoglobin and lipoproteins
Maintaining fluid and electrolyte balance
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
Proteins Transport Substances
Into and Out of Cells
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
The Roles of Body Proteins
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Maintaining acid-base balance
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Buffers
 Acidosis
 Alkalosis
Blood clotting
Providing energy
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
Providing Energy and Glucose
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Inadequate carbohydrate or energy
Amino acids to glucose
Can help maintain blood glucose level
 Urea
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No storage compound for protein
Oversupply of amino acids
Remove amine group
 Use of residues
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Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
Three Different Energy Sources
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
The Fate of an Amino Acid
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Cellular use
Build protein
 Make a needed compound
 Dismantle amino acid for component parts
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Wasting of amino acids
Four conditions
 Preventing waste
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Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
Evaluating Protein and Amino
Acid Supplements
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Protein supplements
Do not improve performance
 Not effective for weight loss
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Amino acid supplements
Body designed to work with whole proteins
 No safe level of amino acid
supplementation
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Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
People Most Likely to Be Harmed
by Amino Acid Supplements
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
Food Protein: Need and Quality
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DRI
 Depends on body size
 Infants
and growing children
 Recommended intake
 Athletes
 Minimum amount
 Upper limit
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Body’s health
Quality
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
Nitrogen Balance
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Nitrogen excreted as compared to
nitrogen eaten
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Levels in healthy adults
Variation in nitrogen balance
Positive balance
 Examples
 Negative balance
 Examples
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Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
Nitrogen Balance
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
Protein Quality
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High-quality proteins
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Limiting amino acids
Complementary proteins
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Enough of all essential amino acids
Mutual supplementation
Protein digestibility
Protein quality
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Fufu
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
Complementary Protein
Combinations
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
Protein Deficiency and Excess
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Consuming too little
protein
Limiting amino acids
 Slows protein
synthesis
 Breakdown of body
tissues
 Consequences
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Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
Protein Deficiency and Excess
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Consuming too much protein
American intake
 Weight loss
 Not the proportion of energy nutrients
 Heart disease
 Animal-derived protein-rich foods
 Adult bone loss
 Cancer
 Low-gluten diet
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Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
Getting Enough but Not Too
Much Protein
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Protein-rich foods
Protein is critical to nutrition
 Displacement of other necessary foods
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Advantages of legumes
Protein
 Vitamin and mineral source
 Soybeans
 Tofu
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Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
Top Contributors of Protein to the
U.S. Diet
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
A Legume
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
Vegetarian and MeatContaining Diets: What Are
the Benefits and Pitfalls?
Controversy 6
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
Introduction
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Affluent countries
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Disease risk
 Benefits of vegetarian diets
Vegetarian lifestyle
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Categorizes by foods they choose to eat
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
Terms Used to Describe
Vegetarian Diets
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
Positive Health Aspects of
Vegetarian Diets
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Other health behaviors associated with
being vegetarian
Obesity
Heart disease
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Blood lipids
High blood pressure
Cancer
Other health benefits
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
Positive Health Aspects of the
Meat Eater’s Diet
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Critical times in life
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Examples
Pregnancy and infancy
Childhood
Adolescence
Aging and illness
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
Planning a Vegetarian Diet

Choosing within the food groups
Protein foods group
 Oils group
 Milk products
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Convenience foods
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
Filling the Vegetarian MyPlate
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney
Planning a Vegetarian Diet
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Vegetarian food patterns
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Ensure adequate intakes
 Protein
 Iron
 Zinc
 Calcium
 Vitamin B12
 Vitamin D
 Omega-3 fatty acids
Nutrition: Concepts & Controversies, 13th edition, Sizer & Whitney