Chapter 6

1. Chapter 6 Protein: Amino Acids © 2008 Thomson - Wadsworth

2. The Chemist’s View of Proteins • Proteins are made from 20 different amino acids, 9 of which are essential. • Each amino acid has an amino group, an acid group, a hydrogen atom, and a side group. • It is the side group that makes each amino acid unique. • The sequence of amino acids in each protein determines its unique shape and function. © 2008 Thomson - Wadsworth

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4. The Chemist’s View of Proteins • Amino Acids • Have unique side groups that result in differences in the size, shape and electrical charge of an amino acid • Nonessential amino acids, also called dispensable amino acids, are ones the body can create. • Nonessential amino acids include alanine, arginine, asparagines, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, and tyrosine. © 2008 Thomson - Wadsworth

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6. The Chemist’s View of Proteins • Amino Acids • Essential amino acids, also called indispensable amino acids, must be supplied by the foods people consume. • Essential amino acids include histidine, isoleucine, leucine, lysine, methionine, phenyalanine, threonine, tryptophan, and valine. • Conditionally essential amino acids refer to amino acids that are normally nonessential but essential under certain conditions. © 2008 Thomson - Wadsworth

7. The Chemist’s View of Proteins • Proteins • Amino acid chains are linked by peptide bonds in condensation reactions. • Dipeptides have two amino acids bonded together. • Tripeptides have three amino acids bonded together. • Polypeptides have more than two amino acids bonded together. • Amino acid sequences are all different, which allows for a wide variety of possible sequences. © 2008 Thomson - Wadsworth

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10. The Chemist’s View of Proteins • Proteins • Protein Shapes • Hydrophilic side groups are attracted to water. • Hydrophobic side groups repel water. • Coiled and twisted chains help to provide stability. © 2008 Thomson - Wadsworth

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12. The Chemist’s View of Proteins • Proteins • Protein Functions • Some carry and store materials. • Some provide strength. • Some require minerals for activation (example: hemoglobin and the mineral iron). • Protein denaturation is the uncoiling of protein that changes its ability to function. • Proteins can be denatured by heat and acid. • After a certain point, denaturation cannot be reversed. © 2008 Thomson - Wadsworth

13. Digestion and Absorption of Protein • Stomach acid and enzymes facilitate the digestion of protein. • It is first denatured, then broken down to polypeptides. • The small intestine continues to break down protein into smaller peptides and amino acids so it can be absorbed. © 2008 Thomson - Wadsworth

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15. Digestion and Absorption of Protein • Protein Digestion • In the Stomach • Protein is denatured by hydrochloric acid. • Pepsinogen (a proenzyme) is converted into its active form pepsin in the presence of hydrochloric acid. • Pepsin cleaves proteins into smaller polypeptides. © 2008 Thomson - Wadsworth

16. Digestion and Absorption of Protein • Protein Digestion • In the Small Intestine • Proteases hydrolyze protein into short peptide chains called oligopeptides, which contain four to nine amino acids. • Peptidases split proteins into amino acids. © 2008 Thomson - Wadsworth

17. Digestion and Absorption of Protein • Protein Absorption • Used by intestinal cells for energy or synthesis of necessary compounds • Transported to the liver • Taking enzyme supplements or consuming predigested proteins is unnecessary © 2008 Thomson - Wadsworth

18. Proteins in the Body • Proteins are versatile and unique. The synthesis of protein is determined by genetic information. • Protein is constantly being broken down and synthesized in the body. • Researchers measure nitrogen balance to study synthesis, degradation and excretion of protein. • Protein has many important functions in the body. • Protein can be used for energy if needed; its excesses are stored as fat. • The study of proteins is called proteomics. © 2008 Thomson - Wadsworth

19. Proteins in the Body • Protein Synthesis • Synthesis is unique for each human being and is determined by the amino acid sequence. • Delivering the instructions through messenger RNA • Carries a code to the nuclear membrane and attaches to ribosomes • Presents a list to make a strand of protein • Transfer RNA lines up the amino acids and brings them to the messenger © 2008 Thomson - Wadsworth

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21. Proteins in the Body • Protein Synthesis • Sequencing errors can cause altered proteins to be made. • An example is sickle-cell anemia where an incorrect amino acid sequence interferes with the cell’s ability to carry oxygen. • Nutrients and Gene Expression - Cells regulate gene expression to make the type of protein needed for that cell. • Epigenetics refers to a nutrient’s ability to activate or silence genes without interfering with the genetic sequence. © 2008 Thomson - Wadsworth

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23. Proteins in the Body • Roles of Proteins • Building Materials for Growth and Maintenance • A matrix of collagen is filled with minerals to provide strength to bones and teeth. • Replaces tissues including the skin, hair, nails, and GI tract lining • Enzymes are proteins that facilitate anabolic (building up) and catabolic (breaking down) chemical reactions. • Hormones regulate body processes and some hormones are proteins. An example is insulin. © 2008 Thomson - Wadsworth

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25. B New compound A B A B A Enzyme Enzyme Enzyme Stepped Art Fig. 6-9, p. 190

26. Proteins in the Body • Roles of Proteins • Regulators of Fluid Balance • Plasma proteins attract water • Maintain the volume of body fluids to prevent edema which is excessive fluid • Maintain the composition of body fluids © 2008 Thomson - Wadsworth

27. Proteins in the Body • Roles of Proteins • Acid-Base Regulators • Act as buffers by keeping solutions acidic or alkaline • Acids are compounds that release hydrogen ions in a solution. • Bases are compounds that accept hydrogen ions in a solution. • Acidosis is high levels of acid in the blood and body fluids. • Alkalosis is high levels of alkalinity in the blood and body fluids. © 2008 Thomson - Wadsworth

28. Proteins in the Body • Roles of Proteins • Transporters • Carry lipids, vitamins, minerals and oxygen in the body • Act as pumps in cell membranes, transferring compounds from one side of the cell membrane to the other © 2008 Thomson - Wadsworth

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30. Proteins in the Body • Roles of Proteins • Antibodies • Fight antigens, such as bacteria and viruses, that invade the body • Provide immunity to fight an antigen more quickly the second time exposure occurs © 2008 Thomson - Wadsworth

31. Proteins in the Body • Roles of Proteins • Source of energy and glucose if needed • Other Roles • Blood clotting by producing fibrin which forms a solid clot • Vision by creating light-sensitive pigments in the retina © 2008 Thomson - Wadsworth

32. Proteins in the Body • A Preview of Protein Metabolism • Protein Turnover and the Amino Acid Pool • Protein turnover is the continual making and breaking down of protein. • Amino acid pool is the supply of amino acids that are available. • Amino acids from food are called exogenous. • Amino acids from within the body are called endogenous. © 2008 Thomson - Wadsworth

33. Proteins in the Body • A Preview of Protein Metabolism • Nitrogen Balance • Zero nitrogen balance is nitrogen equilibrium, when input equals output. • Positive nitrogen balance means nitrogen consumed is greater than nitrogen excreted. • Negative nitrogen balance means nitrogen excreted is greater than nitrogen consumed. © 2008 Thomson - Wadsworth

34. Proteins in the Body • A Preview of Protein Metabolism • Using Amino Acids to Make Proteins or Nonessential Amino Acids – Cells can assemble amino acids into the protein needed. • Using Amino Acids to Make Other Compounds • Neurotransmitters are made from the amino acid tyrosine. • Tyrosine can be made into the melanin pigment or thyroxine. • Tryptophan makes niacin and serotonin. • Using Amino Acids for Energy and Glucose • There is no readily available storage form of protein. • Breaks down tissue protein for energy if needed © 2008 Thomson - Wadsworth

35. Proteins in the Body • A Preview of Protein Metabolism • Deaminating Amino Acids • Nitrogen-containing amino groups are removed. • Ammonia is released into the bloodstream. • Ammonia is converted into urea by the liver. • Kidneys filter urea out of the blood. • Using Amino Acids to Make Fat • Excess protein is deaminated and converted into fat. • Nitrogen is excreted. © 2008 Thomson - Wadsworth

36. Protein in Foods • Eating foods of high-quality protein is the best assurance to get all the essential amino acids. • Complementary proteins can also supply all the essential amino acids. • A diet inadequate in any of the essential amino acids limits protein synthesis. • The quality of protein is measured by its amino acid content, digestibility, and ability to support growth. © 2008 Thomson - Wadsworth

37. Protein in Foods • Protein Quality • Digestibility • Depends on protein’s food source • Animal proteins are 90-99% absorbed. • Plant proteins are 70-90% absorbed. • Soy and legumes are 90% absorbed. • Other foods consumed at the same time can change the digestibility © 2008 Thomson - Wadsworth

38. Protein in Foods • Protein Quality • Amino Acid Composition • The liver can produce nonessential amino acids. • Cells must dismantle to produce essential amino acids if they are not provided in the diet. • Limiting amino acids are those essential amino acids that are supplied in less than the amount needed to support protein synthesis. • Reference Protein is the standard by which other proteins are measured. • Based on their needs for growth and development, preschool children are used to establish this standard. © 2008 Thomson - Wadsworth

39. Protein in Foods • Protein Quality • High-Quality Proteins • Contains all the essential amino acids • Animal foods contain all the essential amino acids. • Plant foods are diverse in content and tend to be missing one or more essential amino acids. • Complementary Proteins • Combining plant foods that together contain all the essential amino acids • Used by vegetarians © 2008 Thomson - Wadsworth

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41. Protein in Foods • Protein Quality • A Measure of Protein Quality - PDCAAS (protein digestibility-corrected amino acid score) • Compares amino acid composition of a protein to human amino acid requirements • Adjusts for digestibility © 2008 Thomson - Wadsworth

42. Protein in Foods • Protein Regulation for Food Labels • List protein quantity in grams • % Daily Values is not required but reflects quantity and quality of protein using PDCAAS. © 2008 Thomson - Wadsworth

43. Health Effects and Recommended Intakes of Protein • Protein deficiency and excesses can be harmful to health. • Protein deficiencies arise from protein-deficient diets and energy-deficient diets. • This is a worldwide malnutrition problem, especially for young children. • High-protein diets have been implicated in several chronic diseases. © 2008 Thomson - Wadsworth

44. Health Effects and Recommended Intakes of Protein • Protein-Energy Malnutrition (PEM) – also called protein-kcalorie malnutrition (PCM) • Classifying PEM • Chronic PEM and acute PEM • Maramus, kwashiorkor, or a combination of the two © 2008 Thomson - Wadsworth

45. Health Effects and Recommended Intakes of Protein • PEM • Marasmus • Infancy, 6 to 18 months of age • Severe deprivation or impaired absorption of protein, energy, vitamins and minerals • Develops slowly • Severe weight loss and muscle wasting, including the heart • < 60% weight-for-age • Anxiety and apathy • Good appetite is possible • Hair and skin problems © 2008 Thomson - Wadsworth

46. Health Effects and Recommended Intakes of Protein • PEM • Kwashiorkor • Older infants and young children, 18 months to 2 years of age • Inadequate protein intake, infections • Rapid onset • Some muscle wasting, some fat retention • Growth is 60-80% weight-for-age • Edema and fatty liver • Apathy, misery, irritability and sadness • Loss of appetite • Hair and skin problems © 2008 Thomson - Wadsworth

47. Health Effects and Recommended Intakes of Protein • PEM • Marasmus-Kwashiorkor Mix • Both malnutrition and infections • Edema of kwashiorkor • Wasting of marasmus © 2008 Thomson - Wadsworth

48. Health Effects and Recommended Intakes of Protein • PEM • Infections • Lack of antibodies to fight infections • Fever • Fluid imbalances and dysentery • Anemia • Heart failure and possible death • Rehabilitation • Nutrition intervention must be cautious, slowly increasing protein. • Programs involving local people work better. © 2008 Thomson - Wadsworth

49. Health Effects and Recommended Intakes of Protein • Health Effects of Protein • Heart Disease • Foods high in animal protein also tend to be high in saturated fat. • Homocysteine levels increase cardiac risks. • Arginine may protect against cardiac risks. © 2008 Thomson - Wadsworth

50. Health Effects and Recommended Intakes of Protein • Health Effects of Protein • Cancer • A high intake of animal protein is associated with some cancers. • Is the problem high protein intake or high fat intake? • Adult Bone Loss (Osteoporosis) • High protein intake associated with increased calcium excretion. • Inadequate protein intake affects bone health also. © 2008 Thomson - Wadsworth