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Protein: Amino Acids
Chapter 6
Whitney & Rolfes – Understanding Nutrition, 12th
Edition
The Chemist’s View of
Proteins
 Atoms
 Carbon, hydrogen, oxygen, nitrogen
 Amino acids
 Carbon
 Hydrogen
 Amino group
 Acid group
 Side group or side chain
Whitney & Rolfes – Understanding Nutrition, 12th Edition
The Chemist’s View of
Proteins
Whitney & Rolfes – Understanding Nutrition, 12th Edition
The Chemist’s View of
Proteins
 More complex than carbohydrates or fats
 Twenty amino acids
 Different characteristics
 Essential amino acids
 Nonessential amino acids
 Conditionally essential
Whitney & Rolfes – Understanding Nutrition, 12th Edition
The Chemist’s View of
Proteins
Whitney & Rolfes – Understanding Nutrition, 12th Edition
The Chemist’s View of
Proteins
 Proteins
 Peptide bonds link amino acids
 Condensation reactions
 Amino acid sequencing
 Primary structure – chemical bonds
 Secondary structure – electrical attractions
 Tertiary structure – hydrophilic & hydrophobic
 Quaternary structure – two or more
polypeptides
Whitney & Rolfes – Understanding Nutrition, 12th Edition
The Chemist’s View of
Proteins
Whitney & Rolfes – Understanding Nutrition, 12th Edition
The Chemist’s View of
Proteins
 Protein
 Denaturation
 Disruption of
stability
 Uncoil and lose
shape
 Stomach acid
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Protein Digestion
 Mouth
 Stomach
 Hydrochloric acid denatures proteins
 Pepsinogen to pepsin
 Small intestine
 Hydrolysis reactions
 Peptidase enzymes
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Protein Digestion
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Protein Absorption
 Transport into intestinal cells
 Uses of amino acids by intestinal cells
 Unused amino acids transported to liver
 Enzyme digestion
 Predigested proteins
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Protein Synthesis
 Uniqueness of each person
 Amino acid sequences of proteins
 Genes – DNA
 Diet
 Adequate protein
 Essential amino acids
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Protein Synthesis
 DNA template to make mRNA
 Transcription
 mRNA carries code to ribosome
 Ribosomes are protein factories
 mRNA specifies sequence of amino acids
 Translation
 tRNA
 Sequencing errors
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Protein Synthesis
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Protein Synthesis
 Gene expression and protein synthesis
 Capability of body cells
 Protein needs
 Dietary influence on gene expression
 Disease development
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Roles of Proteins
 Growth and maintenance
 Building blocks for most body structures
 Collagen
 Replacement of dead or damaged cells
 Enzymes
 Break down, build up, and transform
substances
 Catalysts
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Roles of Proteins
Whitney & Rolfes – Understanding Nutrition, 12th Edition
B
A
A
B
New
compound
A B
Enzyme
The separate compounds,
A and B, are attracted to
the enzyme’s active site,
making a reaction likely.
Enzyme
The enzyme forms a
complex with A and B.
Enzyme
The enzyme is
unchanged, but A and B
have formed a new
compound, AB.
Stepped Art
Fig. 6-9, p. 181
Roles of Proteins
 Hormones
 Messenger molecules
 Transported in blood to target tissues
 Regulators of fluid balance
 Edema
 Acid-base regulators
 Attract hydrogen ions
 Transporters – specificity
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Roles of Proteins
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Roles of Proteins
 Antibodies
 Defend body against disease
 Specificity
 Immunity – memory
 Energy and glucose
 Starvation and insufficient carbohydrate
intake
 Other roles
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Preview of Protein
Metabolism
 Protein turnover & amino acid pool
 Continual production and destruction
 Amino acid pool pattern is fairly constant
 Used for protein production
 Used for energy – if stripped of nitrogen
 Nitrogen balance
 Zero nitrogen balance
 Positive and negative nitrogen balance
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Preview of Protein
Metabolism
 Making other compounds
 Neurotransmitters
 Melanin
 Thyroxin
 Niacin
 Energy and glucose
 Wasting of lean body tissue
 Adequate intake of carbohydrates and fats
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Preview of Protein
Metabolism
 Making fat
 Energy and protein exceed needs
 Carbohydrate intake is adequate
 Can contribute to weight gain
 Deaminating amino acids
 Stripped of nitrogen-containing amino group
 Ammonia
 Keto acid
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Preview of Protein
Metabolism
 Make proteins & nonessential amino acids
 Breakdown of proteins
 Keto-acids
 Liver cells and nonessential amino acids
 Converting ammonia to urea
 Liver – ammonia and carbon dioxide
 Dietary protein
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Preview of Protein
Metabolism
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Preview of Protein
Metabolism
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Preview of Protein
Metabolism
 Excreting urea
 Liver releases urea into blood
 Kidneys filter urea out of blood
 Liver disease
 Kidney disease
 Protein intake and urea production
 Water consumption
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Preview of Protein
Metabolism
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Protein Quality
 Two factors
 Digestibility
 Other foods consumed
 Animal vs. plant proteins
 Amino acid composition
 Essential amino acid consumption
 Nitrogen-containing amino groups
 Limiting amino acid
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Protein Quality
 Reference protein
 Preschool-age children
 High-quality proteins
 Animal proteins
 Plant proteins
 Complementary proteins
 Low-quality proteins combined to provide
adequate levels of essential amino acids
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Protein Regulations for Food
Labels
 Quantity of protein in grams
 Percent Daily Value
 Not mandatory
 Protein claims
 Consumption by children under 4 years old
 Quality of protein
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Protein-Energy Malnutrition
(PEM)
 Insufficient intake of protein, energy, or both
 Prevalent form of malnutrition worldwide
 Impact on children
 Poor growth
 Most common sign of malnutrition
 Impact on adults
 Conditions leading to PEM
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Protein-Energy Malnutrition
(PEM)
 Marasmus
 Chronic PEM
 Children 6 to 18 months
 Poverty
 Little old people – just “skin and bones”
 Impaired growth, wasting of muscles,
impaired brain development, lower body
temperature
 Digestion and absorption
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Protein-Energy Malnutrition
(PEM)
 Kwashiorkor
 Acute PEM
 Children 18 months to 2 years
 Develops rapidly
 Aflatoxins
 Edema, fatty liver, inflammation, infections,
skin and hair changes, free-radical iron
 Marasmus-Kwashiorkor mix
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Protein-Energy Malnutrition
(PEM)
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Protein-Energy Malnutrition
(PEM)
 Infections
 Degradation of antibodies
 Dysentery
 Heart failure and death
 Rehabilitation
 Rehydration and nutrition intervention
 Add protein slowly
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Health Effects of Protein
 High-protein diets
 Heart disease
 Animal-protein intake
 Homocysteine levels
 Arginine levels
 Cancer
 Protein-rich foods; not protein content of diet
 Kidney disease
 Acceleration of kidney deterioration
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Health Effects of Protein
 High-protein diets
 Osteoporosis
 Calcium excretion increases
 Ideal ratio has not been determined
 Animal protein intake
 Weight control
 Satiety
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Recommended Intakes of
Protein
 Need for dietary protein
 Source of essential amino acids
 Practical source of nitrogen
 10 to 35 percent of daily energy intake
 RDA
 Adults = 0.8 grams / kg of body weight / day
 Groups with higher recommended intakes
 Assumptions
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Recommended Intakes of
Protein
 Protein in abundance
 Intake in U.S. and Canada
 Dietary sources
 Serving sizes
 Key diet principle – moderation
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Protein and Amino Acid
Supplements
 Protein powders
 Muscle work vs. protein supplements
 Athletic performance
 Whey protein
 Impact on kidneys
 Amino acid supplements
 Potential risks associated with intake
 Lysine & tryptophan
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Highlight 6
Nutritional Genomics
Whitney & Rolfes – Understanding Nutrition, 12th
Edition
Nutritional Genomics
 New field
 Nutrigenomics
 Nutrients influence gene activity
 Nutrigenetics
 Genes influence activity of nutrients
 Human genome
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Nutritional Genomics
Whitney & Rolfes – Understanding Nutrition, 12th Edition
A Genomics Primer
 DNA
 46 chromosomes
 Nucleotide bases
 Gene expression
 Genetic information to protein synthesis
 Gene presence vs. gene expression
 Epigenetics
 DNA methylation
Whitney & Rolfes – Understanding Nutrition, 12th Edition
A Genomics Primer
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Genetic Variation and Disease
 Genome variation
 About 0.1 percent
 Goal of nutritional genomics
 Customize recommendations that fit
individual needs
 Single-gene disorders
 Phenylketonuria (PKU)
Whitney & Rolfes – Understanding Nutrition, 12th Edition
Genetic Variation and Disease
 Multigene disorders
 Study expression and interaction of multiple
genes
 Sensitive to environmental influences
 Example
 Heart disease
 Single nucleotide polymorphisms (SNPs)
Whitney & Rolfes – Understanding Nutrition, 12th Edition