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Proteins
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Learning Outcomes
• Describe how amino acids form proteins• Define essential and nonessential amino acids and
explain why adequate amounts of each of the essential amino acids are required for protein synthesis
• Distinguish between high quality and low quality proteins and list sources of each
• Describe how 2 low quality proteins can be complementary to each other to provide the required amounts of essential amino acids
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Learning Outcomes
• Explain the methods used to measure the protein quality of foods
• List the factors that influence protein needs. • Calculate the RDA for protein for a healthy adult
with a given body weight• Explain positive nitrogen balance, negative
nitrogen balance and nitrogen equilibrium and list conditions under which they may occur
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Learning Outcomes
• Describe how protein is digested and absorbed in the body
• List the primary functions of protein in the body• Describe types of protein-energy malnutrition• Describe the symptoms and treatment of food
allergies• Develop a vegetarian diet plan that meets the
body’s protein needs
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Structure of Protein
• Contains hydrogen, oxygen, carbon and nitrogen
• Comprised of amino acids– Nitrogen (amino) group– Carboxyl (acid) group)– Hydrogen– Side chain (R)
• Determines protein function and name
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Amino Acids
• Nonessential (dispensable) amino acids– Body can produce
• Essential (indispensable) amino acids– Must be taken in via food
• Conditionally essential amino acids– Essential during infancy, disease or trauma
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Synthesis of Non Essential Amino Acids
• Transamination– Transfer of an amino group from an amino acid
to a carbon skeleton to form a new amino acid
• Deamination– Amino acid losing an amino group– Amino Group is incorporated into urea in the
liver– Excreted in urine
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Complete and Incomplete Proteins
• Complete Proteins– Adequate amounts of all the essential amino acids– Animal proteins, except gelatin
• Incomplete Proteins– Inadequate amounts of 1 or more of the essential amino
acids– Plant proteins, except soybeans
• Complementary Proteins– Combining plant proteins to compensate for limiting
amino acids
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Synthesis of Proteins
• Amino acids are linked by peptide bonds to form proteins
• Synthesis of protein determined through gene expression
• DNA transcription phase– DNA code transferred from the nucleus to the cytosol
via messenger RNA (mRNA)• mRNA translation phase
– tRNA and ribosomes• DNA-coded instructions determine shape, and
thus function of proteins
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Protein Organization• Primary Structure
– Order of amino acids determines shape
• Secondary Structure– Weaker bonds between nearby amino acids
form spiral-lie or pleated sheet shape
• Tertiary Structure– 3D folding determines function
• Quaternary Structure
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Denaturation and Adaptation
• Denaturation of Protein– Altering protein’s 3 dimensional structure– Acid, alkaline, heat, enzymes, or agitation
• Adaptation of Protein Synthesis– Constant state of breakdown, rebuilding and
repair (protein turnover)– In response to diet, exercise, etc.
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Sources of Protein
• Diet and recycling of body protein• North America: 70% supplied by meat,
poultry, fish, milk and milk products, legumes and nuts
• Worldwide: 35% of protein comes from animal
• How do we incorporate more plant protein?
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Evaluation of Food Protein Quality
• Biological Value (BV)– Egg white is highest
• Protein Efficiency Ratio (PER)• Chemical Score• Protein Digestibility Corrected Amino Acid
Score (PDCAAS)
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Recommended Intakes of Protein
• Positive Nitrogen Balance– Protein intake exceeds protein losses
• Negative Nitrogen Balance– Protein losses exceed protein intake
• Equilibrium– Protein intake equals protein losses
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Protein Needs
• AMDR (IOM): 10-35% kcal
• Adult RDA– 0.8g/kg healthy body weight
• Recovery states– 0.8 –2 g/kg body weight
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Protein Digestion and Absorption• Cooking denatures protein• Stomach
– Hydrochloric acid denatures– Pepsin begins enzymatic digestion
• Gastrin controls the release of pepsin
• Small intestine– Secretin and CCK released; stimulate release of
pancreatic proteases (trypsin, chymotrypsin, carboxypeptidases)
• Amino acids absorbed into the portal vein
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Functions of Proteins
• Producing Vital Body Structures• Maintaining Fluid Balance
– Edema
• Contributing to Acid Base Balance– Buffers
• Forming Hormones, Enzymes, and Neurotransmitters
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Functions of Proteins
• Contributing to Immune Function– Anergy is immune incompetence
• Transporting Nutrients• Forming Glucose
– Gluconeogenesis– Muscle wasting is cachexia
• Providing Energy– 4 kcal/g
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Health Concerns Related to Protein Intake
• Protein- Energy Malnutrition (PEM)– Marasmus
• Minimal amounts of energy, protein and other nutrients
– Kwashiorkor• Minimal amounts of protein and moderate energy
deficit
• High-Protein Diets
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Food Protein Allergies
• Food proteins (allergens) cause an immune response, creating an allergic reaction– IgE most commonly produced– anaphylaxix
• 8 foods account for 90% of all food allergies– Peanuts, tree nuts, milk, eggs, fish, shellfish, soy,
and wheat
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Vegetarian Diets
• Types of Vegetarians– Vegan, Lacto-vegetarians, Lacto-ovo-vegetarians
• Nutrient Concerns– B12, Calcium, iron, zinc, vitamin D, high-quality
protein, riboflavin
• Special Concerns for Infants and Children