Chapter 5

1. Chapter 5 The Proteins and Amino Acids © 2007 Thomson - Wadsworth

2. Ask Yourself 1. Protein eaten in excess of need is stored intact in the body, as is fat, so that it can be used when a person’s diet falls short of supplying the day’s need for essential proteins. 2. No new living tissue can be built without protein. 3. Whenever cells are lost, protein is lost. 4. All enzymes and hormones are made of protein. 5. When antibodies enter the body, they produce illness. © 2007 Thomson - Wadsworth

3. Ask Yourself 6. When a person doesn’t eat enough food to meet the body’s energy needs, the body devours its own protein tissue. 7. Once the body has assembled its proteins into body structures, it never lets go of them. 8. Milk protein is the standard against which the quality of other proteins is usually measured. 9. It is impossible to consume too much protein. 10. People who eat no meat have to eat a lot of special foods to get enough protein. © 2007 Thomson - Wadsworth

4. What Proteins Are Made Of • Proteins: compounds—composed of atoms of carbon, hydrogen, oxygen, and nitrogen—arranged as strands of amino acids. Some amino acids also contain atoms of sulfur. • Amino (a-MEEN-o) acids: building blocks of protein; each is a compound with an amine group at one end, an acid group at the other, and a distinctive side chain. • Amine (a-MEEN): group the nitrogen-containing portion of an amino acid. © 2007 Thomson - Wadsworth

5. Nine essential amino acids: Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Threonine Tryptophan Valine Essential amino acids: amino acids that cannot be synthesized by the body or that cannot be synthesized in amounts sufficient to meet physiological need. What Proteins Are Made Of © 2007 Thomson - Wadsworth

6. What Proteins Are Made Of • Protein synthesis: the process by which cells assemble amino acids into proteins. • Each individual is unique because of minute differences in the ways his or her body proteins are made. • The instructions for making every protein in a person’s body are transmitted in the genetic information the person receives at conception. • Peptide bond: a bond that connects one amino acid with another. © 2007 Thomson - Wadsworth

7. What Proteins Are Made Of • Proteins are made of many different amino acid units hooked to each other. • Strands of proteins are tangled chains, globular in structure. • The differing shapes of proteins enable them to perform different tasks in the body. • Proteins may repel or attract water. • Some proteins contain minerals or vitamins. • Several proteins may gather to form a functional group. © 2007 Thomson - Wadsworth

8. What Proteins Are Made Of • Denaturation: the change in shape of a protein brought about by heat, alcohol, acids, bases, salts of heavy metals, or other agents. • First step in the protein’s breakdown. • Useful to the body in digestion. • Stomach acid opens up the protein’s structure, allowing digestive enzymes to cleave peptide bonds. Cooking an egg denatures its proteins. © 2007 Thomson - Wadsworth

9. Functions of Body Proteins • No living tissue can be built without protein. • Protein is part of every living cell. • Proteins account for about 20% of our body weight. • Proteins come in many forms and perform many vital functions. © 2007 Thomson - Wadsworth

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11. Functions of Body Proteins • Amino acids are constantly needed for the body to build the proteins of new tissue during growth and maintenance. • Examples of growth: a developing embryo; a growing child. • Examples of maintenance: replacing blood lost to burns, hemorrhage, or surgery; developing scar tissue that heals wounds; replacing hair or nails; replacing cells that are worn out. • Amino acids must constantly be resupplied by food for new growth to occur. © 2007 Thomson - Wadsworth

12. Functions of Body Proteins • Proteins form vital parts of most of our body structures. • Examples of body structures include skin, hair, nails, membranes, muscles, teeth, bones, organs, ligaments and tendons. © 2007 Thomson - Wadsworth

13. Functions of Body Proteins Enzyme ActionEach enzyme facilitates a specific chemical reaction. © 2007 Thomson - Wadsworth

14. Functions of Body Proteins • Hormones: chemical messengers. • Hormones are secreted by a variety of glands in the body in response to altered conditions. • Each affects one or more target tissues or organs and elicits specific responses to restore normal conditions. © 2007 Thomson - Wadsworth

15. Functions of Body Proteins • Antibodies: large proteins of the blood and body fluids, produced by one type of immune cell in response to invasion of the body by unfamiliar molecules (mostly foreign proteins). • Antibodies inactivate the foreign substances and so protect the body. • The foreign substances are called antigens. • Immunity: specific disease resistance derived from the immune system’s memory of prior exposure to specific disease agents and its ability to mount a swift response against them. • Malnutrition injures the immune system. © 2007 Thomson - Wadsworth

16. An optimal diet helps to provide strength and support to the body’s immune system. © 2007 Thomson - Wadsworth

17. Functions of Body Proteins • Fluid balance: distribution of fluid among body compartments. • Shown here are the fluids within and surrounding a cell. Body proteins help hold fluid within cells, tissues, and blood vessels. © 2007 Thomson - Wadsworth

18. Functions of Body Proteins • Acid-Base Balance:equilibrium between acid and base concentrations in the body fluids. • Acid-base balance of blood is carefully controlled. • Normal body processes continually produce acids and bases. • Acids: compounds that release hydrogens in a watery solution; acids have a low pH. • Bases: compounds that accept hydrogens from solutions; bases have a high pH. © 2007 Thomson - Wadsworth

19. pH Values of Selected Fluids A fluid’s acidity or alkalinity is measured in pH units. • pH: the concentration of hydrogen ions. The lower the pH, the stronger the acid • pH 2 is a strong acid, • pH 7 is neutral, and • pH above 7 is alkaline. © 2007 Thomson - Wadsworth

20. Functions of Body Proteins Acid-Base Balance • Acidosis (a-sih-DOSE-sis): blood acidity above normal, indicating excess acid. • Alkalosis (al-kah-LOH-sis): blood alkalinity above normal. • Buffers: compounds that help keep a solution’s acidity (amount of acid) or alkalinity (amount of base) constant. • Some proteins act as buffers to maintain normal blood pH. © 2007 Thomson - Wadsworth

21. Functions of Body Proteins Transport Proteins specialize in moving nutrients and molecules into and out of cells. • The “sodium-potassium pump” is switched on and off by hormones. • Special proteins carry vitamins, minerals. • Lipoproteins carry lipids. © 2007 Thomson - Wadsworth

22. Functions of Body Proteins Protein As Energy: • In the absence of adequate energy, the body will sacrifice protein to provide energy. • The amine group will be degraded, incorporated by the liver into urea, and sent to the kidneys for excretion in urine. • Urea (yoo-REE-uh): the principal nitrogen excretion product of metabolism, generated mostly by the removal of amine groups from unneeded amino acids or from those amino acids being sacrificed to a need for energy. © 2007 Thomson - Wadsworth

23. Functions of Body Proteins Protein As Energy: • After the amine group is removed, the remaining carbon, hydrogen and oxygen will be used for immediate energy. • Protein sparing:a description of the effect of carbohydrate and fat, which, by being available to yield energy, allow amino acids to be used to build body proteins. • Excess amino acids are not stored by the body. • After removing the amine group, the excess is converted to glycogen or fat for energy storage. © 2007 Thomson - Wadsworth

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25. How the Body Handles Protein • By the time proteins slip into the small intestine, they are already broken into different-sized pieces. • Some single amino acids and many strands of two, three, or more amino acids. • There are dipeptides, tripeptides, and longer chains. © 2007 Thomson - Wadsworth

26. How the Body Handles Protein • Amino acids pass from the absorptive cells in the small intestine into the bloodstream, where they can be taken up by cells and used to make proteins. • Amino acid strands are assembled to make proteins. • Nonessential amino acids can be manufactured by the body from fragments of other amino acids. • If essential amino acids are missing, protein building will halt. © 2007 Thomson - Wadsworth

27. Protein Quality of Foods • Important characteristics of dietary protein: • Should supply at least the essential amino acids. • Should supply enough other amino acids to make nitrogen available for synthesizing other nonessential amino acids. • Should provide adequate food energy to prevent sacrifice of amino acids for energy. © 2007 Thomson - Wadsworth

28. Protein Quality of Foods • Complete proteins: proteins containing all the essential amino acids in the right proportion relative to need. The quality of a food protein is judged by the proportions of essential amino acids that it contains relative to our needs. Animal proteins are the highest in quality. • Incomplete protein: a protein lacking or low in one or more of the essential amino acids. • Limiting amino acid: a term given to the essential amino acid in shortest supply (relative to the body’s need) in a food protein; it therefore limits the body’s ability to make its own proteins. © 2007 Thomson - Wadsworth

29. Protein Quality of Foods • Protein quality: a measure of the essential amino acid content of a protein relative to the essential amino acid needs of the body. • Biological value (BV): a measure of protein quality, assessed by determining how well a given food or food mixture supports nitrogen retention. • Reference protein: egg white protein, the standard with which other proteins are compared to determine protein quality. © 2007 Thomson - Wadsworth

30. Protein Quality of Foods • Complementary proteins: two or more food proteins whose amino acid assortments complement each other in such a way that the essential amino acids limited in or missing from each are supplied by the others. Both meals shown supply an adequate assortment of amino acids © 2007 Thomson - Wadsworth

31. Protein Quality of Foods HOW TWO PLANT PROTEINS COMBINE TO YIELD A COMPLETE PROTEIN: • Two incomplete proteins (for example, legumes plus grains) can be combined to equal a complete protein (peanut butter sandwich). In this example, • the peanut butter provides adequate amounts of the amino acid lysine, but is lacking in methionine. • The bread “complements” the peanut butter because it contains adequate methionine, but is lacking in lysine. • When combined as a sandwich, all essential amino acids are present. © 2007 Thomson - Wadsworth

32. Recommended Protein Intakes • Recommended protein intakes can be stated by two methods. • As a percentage of total calories: • Protein should provide 10-35% of total calories. • As an absolute number (grams per day). • A healthy adult should consume 0.8 gram per kilogram of desirable body weight per day. © 2007 Thomson - Wadsworth

33. Recommended Protein Intakes To calculate the percentage of calories you derive from protein: • Use your total calories as the denominator (example: 1,900 cal). • Multiply your total protein intake in grams by 4 cal/g to obtain calories from protein as the numerator (example: 70 g protein X 4 cal/g = 280 cal). • Divide to obtain a decimal, multiply by 100, and round off (example: 280/1,900 X 100 = 15% cal from protein). © 2007 Thomson - Wadsworth

34. Recommended Protein Intakes To figure your recommended protein intake (RDA): • Find the desirable weight for a person your height (see Appendix B). Assume this weight is appropriate for you. • Change pounds to kilograms (divide pounds by 2.2; one kilogram = 2.2 pounds). • Multiply kilograms by 0.8 g/kg. • Example (for a 5’8” male): 1. Desirable weight: about 150 lb. 2. 150 lb. divide by 2.2 lb. = 68 kg (rounded off). 3. 68 kg X 0.8 g/kg = 54 g protein (rounded off). © 2007 Thomson - Wadsworth

35. Protein and Health • Protein deficiency and energy deficiency go hand in hand so often that public health officials have given a nickname to the pair. • Protein-energy malnutrition (PEM), also called protein-calorie malnutrition (PCM): the world’s most widespread malnutrition problem, including both kwashiorkor and marasmus. © 2007 Thomson - Wadsworth

36. Protein and Health • Kwashiorkor (kwash-ee-OR-core): a deficiency disease caused by inadequate protein in the presence of adequate food energy. • Edema (eh-DEEM-uh): swelling of body tissue caused by leakage of fluid from the blood vessels, seen in (among other conditions) protein deficiency. © 2007 Thomson - Wadsworth

37. Protein and Health • Marasmus (ma-RAZ-mus): an energy deficiency disease; starvation. • Dysentery (DISS-en-terry): an infection of the digestive tract that causes diarrhea. • Acquired immune deficiency syndrome (AIDS): an immune system disorder caused by the human immunodeficiency virus (HIV). © 2007 Thomson - Wadsworth

38. Protein and Health Too Much Protein • The problems of protein excess can be found in developed countries. • Possible to overload the liver and kidneys. • Can promote calcium excretion. • Excess protein can be converted to energy and stored as body fat. • No apparent benefit to consuming too much protein when caloric intake is adequate. © 2007 Thomson - Wadsworth

39. Protein and Health Foods that supply protein in abundance are shown here in the Milk Group and the Meat & Beans Group of the MyPyramid Food Guide (top two photos). Servings of foods from the Vegetable Group and the Grains Group can also contribute protein to the diet (bottom two photos). © 2007 Thomson - Wadsworth

40. Protein contributed by food groups in the average U.S. diet © 2007 Thomson - Wadsworth

41. Protein and Health • The average protein consumption in the United States is 67.5 grams of protein per day or about 15% of total caloric intake, of which: • 37 grams (55%) come from the Meat & Beans Group. • The Milk and Grains Groups are the next two largest contributors, providing 36% of the total daily protein. © 2007 Thomson - Wadsworth

42. Enjoy adding more legumes to your weekly meals. • Enjoy a variety of dried, beans, peas, and lentils when dining out. © 2007 Thomson - Wadsworth

43. Protein and Health • Legumes(leg-GYOOMS): plants of the bean and pea family having roots with nodules that contain bacteria that can trap nitrogen from the air in the soil and make it into compounds that become part of the seed. • The seeds are rich in high-quality protein compared with those of most other plant foods. © 2007 Thomson - Wadsworth

44. The New American Plate: • In the Kitchen: • Small meat portions tend to work best mixed into dishes with lots of vegetables and grains… • In the Lunch Box: • Take a thermos filled with chili, vegetable soup, or a milk-based soup, such as cream of tomato, prepared with nonfat milk instead of a sandwich… • At the Table: • Make whole grains, vegetables, and legumes the main event of your meals… © 2007 Thomson - Wadsworth

45. The Vegetarian Diet • Well-planned, plant-based meals consisting of: • A variety of whole grains • Legumes and nuts • Vegetables and fruits • Eggs and dairy products (for some vegetarians) • Can offer sound nutrition and health benefits to vegetarians and non-vegetarians alike © 2007 Thomson - Wadsworth

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48. The Vegetarian Diet • Nutritional yeast: a fortified food supplement containing B vitamins, iron, and protein that can be used to improve the quality of a vegetarian diet. • Meat replacements: textured vegetable protein products formulated to look and taste like meat, fish, or poultry. • Many of these are designed to match the known nutrient contents of animal protein foods. © 2007 Thomson - Wadsworth

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50. Food Allergy—Nothing to Sneeze At • Food aversion: a strong desire to avoid a particular food. • Food allergy: an adverse reaction to an otherwise harmless substance that involves the body’s immune system. • Food intolerance: a general term for any adverse reaction to a food or food component that does not involve the body’s immune system. • Adverse reaction: an unusual response to food, including food allergies and food intolerances. • Food allergen: a substance in food— usually a protein—that is seen by the body as harmful and causes the immune system to mount an allergic reaction. © 2007 Thomson - Wadsworth