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Proteins 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 2 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 3 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 4 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 5 6 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 7 8 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 9 10 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 11 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 12 13 14 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 15 16 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. 17 18 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? 19 20 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) 21 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 22 23 Protein Needs • AMDR (IOM): 10-35% kcal • Adult RDA – 0.8g/kg healthy body weight • Recovery states – 0.8 –2 g/kg body weight 24 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 25 26 27 Functions of Proteins • Producing Vital Body Structures • Maintaining Fluid Balance – Edema • Contributing to Acid Base Balance – Buffers • Forming Hormones, Enzymes, and Neurotransmitters 28 29 30 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 31 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 32 33 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 34 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 35