Proteins

2 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

3 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

4 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

5 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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7 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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9 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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11 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

12 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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15 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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17 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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19 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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21 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)

22 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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24 Protein Needs AMDR (IOM): 10-35% kcal Adult RDA – 0.8g/kg healthy body weight Recovery states –0.8 –2 g/kg body weight

25 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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28 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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31 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

32 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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34 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

35 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