Chapter 5: Protein
- 1. Protein 55 Copyright © 2017 Cengage Learning. All Rights Reserved.
- 2. © Cengage Learning 2017 Introduction • Proteins are “of prime importance” • Versatile roles – Facilitate chemical reactions – Fight infections – Provide structure in all living tissue Copyright © 2017 Cengage Learning. All Rights Reserved.
- 3. © Cengage Learning 2017 The Chemist’s View of Proteins • Comprised of carbon, hydrogen, oxygen, and nitrogen atoms – Amino: nitrogen containing • The structure of proteins – Amino acids: protein building blocks – About 20 different amino acids in proteins – Protein chains: dipeptides, tripeptides, polypeptides Copyright © 2017 Cengage Learning. All Rights Reserved.
- 4. © Cengage Learning 2017 Amino Acid Structure and Examples of Amino Acids Copyright © 2017 Cengage Learning. All Rights Reserved.
- 5. © Cengage Learning 2017 The Chemist’s View of Proteins (cont’d.) • The structure of proteins – Protein shapes • Amino acid chains fold into complex shapes • What determines the shape of polypeptide chains? – Protein functions • Different shapes enable proteins to perform different tasks in the body Copyright © 2017 Cengage Learning. All Rights Reserved.
- 6. © Cengage Learning 2017 The Coiling and Folding of a Protein Molecule Copyright © 2017 Cengage Learning. All Rights Reserved.
- 7. © Cengage Learning 2017 The Structure of Hemoglobin Copyright © 2017 Cengage Learning. All Rights Reserved.
- 8. © Cengage Learning 2017 The Chemist’s View of Proteins (cont’d.) • Nonessential and essential amino acids – Nonessential amino acids: those the body can make for itself – Essential amino acids: those that must be obtained in foods – What is a conditionally essential amino acid? Copyright © 2017 Cengage Learning. All Rights Reserved.
- 9. © Cengage Learning 2017 Protein Digestion and Absorption • Long peptide chains + enzymes • Short peptides + enzymes • Tripeptides and dipeptides + enzymes • Amino acids Copyright © 2017 Cengage Learning. All Rights Reserved.
- 10. © Cengage Learning 2017 Protein Turnover and Nitrogen Balance • Protein turnover – Continual process in which proteins are made and broken down – What are some specific examples? – Amino acids needed each day to support new growth and maintenance of cells • Nitrogen balance (N in vs. N out) – Nitrogen equilibrium: intake equals output Copyright © 2017 Cengage Learning. All Rights Reserved.
- 11. © Cengage Learning 2017 Roles of Body Proteins • As structural components – Muscle, bones, teeth, tendons, cartilage, blood vessels, etc. • As enzymes – Catalysts essential to all life processes – Protein circle • Some break food proteins into amino acids • Others build long chains of amino acids (proteins) Copyright © 2017 Cengage Learning. All Rights Reserved.
- 12. © Cengage Learning 2017 Copyright © 2017 Cengage Learning. All Rights Reserved.
- 13. © Cengage Learning 2017 Roles of Body Proteins (cont’d.) • As transporters: move substances around the body – Protein hemoglobin: carries oxygen – Lipoproteins: transport lipids • As regulators of fluid and electrolyte balance – Maintain necessary amounts and types of fluid and minerals in each compartment Copyright © 2017 Cengage Learning. All Rights Reserved.
- 14. © Cengage Learning 2017 One Cell and Its Associated Fluids Copyright © 2017 Cengage Learning. All Rights Reserved.
- 15. © Cengage Learning 2017 Roles of Body Proteins (cont’d.) • As regulators of fluid and electrolyte balance – Proteins can help control fluid distribution this because they: • Can’t move freely across membranes • Are attracted to water – Cell membrane transport proteins transfer electrolytes and other substances into and out of cells to maintain balance Copyright © 2017 Cengage Learning. All Rights Reserved.
- 16. © Cengage Learning 2017 Roles of Body Proteins (cont’d.) • As regulators of acid-base balance – Maintain the balance between acids and bases within the body’s fluids – What are acidosis and alkalosis? • As antibodies – Giant protein molecules produced when body detects antigens; specific to those antigens – What is immunity? Copyright © 2017 Cengage Learning. All Rights Reserved.
- 17. © Cengage Learning 2017 Roles of Body Proteins (cont’d.) • As hormones – Chemical messengers (some are proteins, e.g., insulin, glucagon) • As a source of energy and glucose – When glucose or fatty acids are limited – Starvation results in wasting of lean tissue • Functions of proteins summarized in Table 5-2 Copyright © 2017 Cengage Learning. All Rights Reserved.
- 18. © Cengage Learning 2017 Protein and Health • Protein deficiency – Slow growth in children, impaired brain and kidney function, weakened immune defenses, and impaired nutrient absorption – Malnutrition • Protein-energy malnutrition (PEM) • Severe acute malnutrition (SAM): kwashiorkor and marasmus • Chronic malnutrition Copyright © 2017 Cengage Learning. All Rights Reserved.
- 19. Copyright © 2017 Cengage Learning. All Rights Reserved.
- 20. © Cengage Learning 2017 Protein and Health (cont’d.) • Malnutrition – Severe acute malnutrition • Wasting: thinness for height, indicating recent rapid weight loss – Chronic malnutrition • Stunting: low height for age, indicating restriction of potential growth in children – Rehabilitation • What are ways to prevent and treat malnutrition? Copyright © 2017 Cengage Learning. All Rights Reserved.
- 21. © Cengage Learning 2017 Protein and Health (cont’d.) • Protein excess – Heart disease • Animal-derived food sources high in saturated fat can contribute to heart disease, obesity, and diabetes risk – Kidney disease • High protein intakes can accelerate loss of kidney function in chronic kidney disease Copyright © 2017 Cengage Learning. All Rights Reserved.
- 22. © Cengage Learning 2017 Protein and Health (cont’d.) • Protein and amino acid supplements – Protein supplements • Not needed by well-fed athletes • Use in weight loss unsupported by scientific studies – Amino acid supplements • The body absorbs amino acids from whole proteins best Copyright © 2017 Cengage Learning. All Rights Reserved.
- 23. © Cengage Learning 2017 Protein and Health (cont’d.) • Protein recommendations and intakes – RDA (adults): 0.8 gram per kilogram (2.2 pounds) of healthy body weight – AMDR: 10% to 35% percent of kcalories – Typical U.S. intakes • Men: 16% of kcalories • Women, children, and some elderly: 13% to 15% of kcalories Copyright © 2017 Cengage Learning. All Rights Reserved.
- 24. © Cengage Learning 2017 Protein in Foods • Protein quality – High-quality proteins provide adequate amounts of all of the essential amino acids – Digestibility: measure of absorption – Amino acid composition • Limiting amino acid: essential amino acid available in the shortest supply relative to the amount needed to support protein synthesis Copyright © 2017 Cengage Learning. All Rights Reserved.
- 25. Copyright © 2017 Cengage Learning. All Rights Reserved.
- 26. Copyright © 2017 Cengage Learning. All Rights Reserved.
- 27. © Cengage Learning 2017 Protein in Foods (cont’d.) • Protein quality – High-quality proteins • Generally derived from animal foods • Soy protein – Complementary proteins • Two protein-rich foods with different amino acids combined to obtain all the essential amino acids in amounts sufficient to support health Copyright © 2017 Cengage Learning. All Rights Reserved.
- 28. © Cengage Learning 2017 Complementary Proteins Copyright © 2017 Cengage Learning. All Rights Reserved.
- 29. © Cengage Learning 2017 Protein in Foods (cont’d.) • Protein sparing – Carbohydrate and fat allow amino acids to be used to build body proteins – If they are insufficient, the body will use protein to meet energy needs • Protein on food labels – Quantity required – % Daily Value reflects quantity and quality Copyright © 2017 Cengage Learning. All Rights Reserved.
- 30. © Cengage Learning 2017 Nutrition in Practice: Vegetarian Diets • Protein: varied plant protein foods • Appropriate energy intake • Vitamin B12: fortified foods/ supplements • Vitamin D: adequate sun, fortified foods • Iron absorption increased by vitamin C • Zinc: legumes, enriched foods, whole grains Copyright © 2017 Cengage Learning. All Rights Reserved.
- 31. © Cengage Learning 2017 Nutrition in Practice: Vegetarian Diets • Calcium: dark green leafy vegetables, legumes, fortified foods, almonds, sesame seeds • Essential fatty acids: flaxseed, walnuts, their oils; soybeans, canola oil – EPA and DHA: algal oils • Health advantages of vegetarian diets Copyright © 2017 Cengage Learning. All Rights Reserved.
Editor's Notes
- #5: Figure 5-1 Amino Acid Structure and Examples of Amino Acids All amino acids have a “backbone” made of an amino acid group (which contains nitrogen) and an acid group. The side group varies from one amino acid to the next. Note that the side group is a unique structure that differentiates one amino acid from another.
- #6: Answer: An amino acid has characteristics that attract it to or repel it from surrounding fluids and other amino acids. These attracting and repelling forces cause the chain to fold into the protein’s shape.
- #7: Figure 5-2 The Coiling and Folding of a Protein Molecule
- #8: Figure 5-3 The Structure of Hemoglobin Four highly folded polypeptide chains form the globular hemoglobin protein.
- #9: Answer: An amino acid that is normally nonessential but must be supplied by the diet in special circumstances when the need for it becomes greater than the body’s ability to produce it.
- #11: Example answer: Cell proteins are broken down into amino acids, which are reused within the cell or released into the blood, from which other cells can pick them up and reuse them.
- #13: Figure 5-4 Enzyme Action Each enzyme facilitates a specific chemical reaction. In this diagram, an enzyme enables two compounds to make a more complex structure, but the enzyme itself remains unchanged.
- #15: Figure 5-5 One Cell and Its Associated Fluids
- #17: Answers: Acidosis is acid accumulation in the blood and fluids, which can depress the CNS; alkalosis is excessive base in the blood and body fluids. Both can cause protein denaturation (very dangerous). Immunity is the body’s ability to defend itself against diseases, which involves the “molecular memory” of antibody-producing immune cells. These cells collectively “remember” how to produce antibodies for each antigen they have encountered, and can thus manufacture them more quickly at the second and subsequent exposures to the antigen.
- #20: Table 5-3 Severe Acute Malnutrition and Chronic Malnutrition Compared
- #21: Answer: Prevention methods include encouraging breastfeeding and appropriate complementary feeding of infants and children. Treatment involves administering specially formulated fluids and foods; for SAM, hospitalization with intensive nursing care, medical nutrition therapy, and medication is necessary.
- #26: Table 5-5 Protein-Containing Foods
- #27: Table 5-5 Protein-Containing Foods (cont’d.)
- #29: Figure 5-7 Complementary Proteins In general, legumes provide plenty of isoleucine (Ile) and lysine (Lys) but fall short in methionine (Met) and tryptophan (Trp). Grains have the opposite strengths and weaknesses, making them a perfect match for legumes.