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