Chapter 6 The Proteins and Amino Acids

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Chapter 6The Proteins and Amino Acids

• Nutrition Concepts Controversies, 12e
  Sizer/Whitney

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Learning Objectives

• Describe why some amino acids are essential,
  nonessential, or conditionally essential to the
  human body, and state the outcome should any one
  of them be lacking in the diet.
• Compare the digestion of protein and transport of
  amino acids with digestion and transport of
  lipids in the body.
• Discuss the roles that various proteins and amino
  acids can play in the body.

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Learning Objectives

• Describe the fate of amino acids consumed with a
  balanced diet versus a carbohydrate-poor diet.
• Discuss the concept of nitrogen balance and
  compute the amount of protein needed for a
  healthy college student.

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Learning Objectives

• Identify the major forms of protein malnutrition,
  and discuss reasons why consuming too much
  protein is not recommended.
• Summarize the health advantages and nutritional
  risks of a vegan diet.
• Develop a lacto-ovo vegetarian diet plan that
  meets all nutrient requirements for a given
  individual.

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The Structure of Proteins

• 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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How Do Amino Acids Build Proteins?

• Peptide bonds
• Link amino acids
• Strands of amino acids do not remain straight
• Coils
• Folds
• Side chain electrical charge
• Activation

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The Coiling and Folding of a Protein Molecule
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The Structure of Hemoglobin
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The Variety of Proteins

• Protein shapes enable performance of different
  tasks
• Examples
• Protein strands alone or in association
• Inherited amino acid sequences
• Alterations to sequence
• Sickle-cell disease
• Nutrients and gene expression

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Normal Red Blood Cells and Sickle Cells
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Protein Synthesis
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Denaturation of Proteins

• Denaturing agents
• Digestion
• Stomach acid
• Dangers of denaturation

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Protein Digestion

• Stomach
• Denatures protein in food
• Uncoil proteins strands
• Enzymes attack peptide bonds
• Small intestine
• Polypeptides
• Further break down
• Common misconceptions

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A Dipeptide and Tripeptide
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How Protein in Food Becomes Amino Acids in the
Body
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Amino Acid Absorption

• Absorbed by cells of small intestine
• Larger molecules
• Hormones or allergens
• Separate sites for absorption
• Released into the bloodstream
• Carried to the liver

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The Importance of Protein

• Amino acids must be continually available
• Building of new proteins
• Amino acids are needed each day
• Protein turnover

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Roles of Body Proteins

• Regulation of gene expression
• Providing structure and movement
• Muscle tissue
• Other structural proteins
• Building enzymes, hormones, other compounds
• Building antibodies

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Enzyme Action
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Amino Acid Sequence of Human Insulin
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Roles of Body Proteins

• Transporting substances
• Hemoglobin and lipoproteins
• Maintaining fluid and electrolyte balance
• Edema
• Maintaining acid-base balance
• Blood clotting
• Providing energy and glucose

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Proteins Transport Substances Into and Out of
Cells
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Amino Acids to Glucose

• Protein can help maintain blood glucose levels
• No storage compound for protein
• Dismantle tissue proteins
• Oversupply of amino acids
• Remove amine group
• Use of residues

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Three Different Energy Sources
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Amino Acids to Glucose

• Fate of an amino acid
• Cellular use
• Build protein
• Make a needed compound
• Dismantle amino acid for component parts
• Wasting of amino acids
• Preventing waste

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Protein and Amino Acid Supplements

• Protein supplements
• Do not improve performance
• Not effective for weight loss
• Amino acid supplements
• Body designed to work with whole proteins
• No safe level of amino acid supplementation

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People Most Likely to Be Harmed by Amino Acid
Supplements
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How Much Protein Do People Really Need?

• DRI
• Depends on body size
• Infants and growing children
• Recommended intake
• Vegetarians
• Minimum amount
• Upper limit
• Bodys health
• Quality

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Nitrogen Balance

• Nitrogen excreted as compared to nitrogen eaten
• Levels in healthy adults
• Variation in nitrogen balance
• Positive balance
• Examples
• Negative balance
• Examples

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Nitrogen Balance
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Which Foods Provide High Quality Protein?

• High-quality proteins
• Enough of all essential amino acids
• Limiting amino acids
• Complementary proteins
• Mutual supplementation
• Protein digestibility
• Animal proteins
• Legumes

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Complementary Protein Combinations
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Protein Deficiency and Excess

• Worlds leading form of malnutrition
• Combined with energy deficiencies
• Protein-energy malnutrition (PEM)
• Locations of prevalence
• Effects of PEM
• Children and adults
• Two forms

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Protein Deficiency and Excess

• Marasmus
• Common in children
• Muscle wasting
• Impairments
• Disease conditions
• Preventing death
• Heart failure

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Protein Deficiency and Excess

• Kwashiorkor
• Weaning of babies
• Fluid balance is diminished
• Changes in body
• Risk of infection
• PEM at home

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Protein Deficiency and Excess

• Overconsumption of protein-rich foods
• Possible health risks
• U.S. protein intakes
• Heart disease
• Homocysteine
• Kidney disease
• Adult bone loss
• Cancer

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Getting Enough but Not Too Much Protein

• Protein-rich foods
• Protein is critical to nutrition
• Displacement of other necessary foods
• Advantages of legumes
• Protein
• Vitamin and mineral source
• Soybeans

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Top Contributors of Protein to the U.S. Diet
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A Legume
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Vegetarian and Meat-Containing Diets What Are
the Benefits and Pitfalls?

• Controversy 6

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Vegetarian Diets

• Reasons to choose a vegetarian lifestyle
• Categorization of vegetarians
• By foods they choose to eat
• Reasons why meat eaters choose to eat meat

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Terms Used to Describe Vegetarians and Their Diets
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Positive Health Aspects of Vegetarian Diets

• Other health behaviors associated with being
  vegetarian
• Obesity
• Heart disease
• Blood lipids
• Hypertension
• Cancer
• Other health benefits

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Positive Health Aspects of the Meat Eaters Diet

• Critical times in life
• Examples
• Pregnancy and infancy
• Childhood
• Adolescence
• Aging

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Planning a Vegetarian Diet

• Vegetarian food guides
• Ensure adequate intakes
• Protein
• Iron
• Zinc
• Calcium
• Vitamin B12
• Vitamin D
• Omega-3 fatty acids

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My Vegetarian Food Pyramid
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Nutrients in Nonfat Milk and Light Soy Milk