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CH 6: Proteins and Amino Acids

CH 6: Proteins and Amino Acids. Proteins. Consider last as protein is the body’s least desirable source of energy 4 kcal/gram When body uses protein for energy it is not available to perform other critical functions No protein stores – all protein has a function in the body.

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CH 6: Proteins and Amino Acids

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  1. CH 6: Proteins and Amino Acids

  2. Proteins • Consider last as protein is the body’s least desirable source of energy • 4 kcal/gram • When body uses protein for energy it is not available to perform other critical functions • No protein stores – all protein has a function in the body

  3. Chemical Nature 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. • Amino acids all contain the elements: C, H, O, N • Carbs and lipids do not contain N • Cannot make protein from carbs and lipids

  4. © 2008 Thomson - Wadsworth

  5. Chemical Nature of Proteins • Proteins are chains of amino acids (a.a.) joined by peptide bonds • Order of the a.a. is determined by your DNA • The sequence of amino acids in each protein determines its unique shape and function. • For the protein to function the amino acids must be in the correct order and the chain must fold up properly

  6. © 2008 Thomson - Wadsworth

  7. © 2008 Thomson - Wadsworth

  8. Amino Acids • The body cannot make 9 of the amino acids – these are the essential amino acids • These amino acids must be supplied by the diet • The body can make 11 of the amino acids • These are the nonessential a.a. • Some amino acids are conditionally essential, required under certain conditions

  9. Amino Acids • Diet must provide all 9 of the essential a.a. on a regular/daily basis for proteins to be made • Need all 20 a.a. to make most proteins • Animal sources of proteins contain all 9 essential aa (one exception) • Plant sources are missing or low in at least one essential aa (one exception) – page 188

  10. Protein Intake • Recommended level of intake is expressed 2 ways: • 10 – 25 % daily caloric intake • 0.8 grams protein per kg body weight (RDA) • Computer programs use this value • Most meet this level EASILY

  11. Protein Function • Growth, maintenance, and repair of body tissue • Need protein to make muscles, skin, hair, blood vessels…….. • Cannot grow without protein • Replace lining of GI tract every 3 days (maintenance example)

  12. Protein Function • Enzymes • Enzymes are proteins that catalyze (speed up) chemical reactions • Every reaction in the body requires a specific enzyme

  13. Protein Function • Hormones • Hormones are chemical messengers • Travel to target cells/organs and ilicit a response • Examples: • Insulin and glucagon • Growth hormone • Thyroxin – regulates metabolic rate

  14. Protein Function • Antibodies • Component of immune system • Attack foreign substances in the body

  15. Protein Function • Transportation of Substances • Proteins are needed to transport lipids in the blood • Proteins are needed to transport substances across cell membranes • Need for nerve and muscle contraction • Proteins are needed to absorb calcium and iron

  16. Protein Function • Fluid Balance • Proteins attract water • Proteins are too big to pass through plasma membranes or out of capillaries • The water moves in and out of the blood • If protein levels in the blood drop, water leaks out of the blood into surrounding tissues  edema

  17. Protein Function • Fluid Balance • Generally proteins do not leave their compartments • Fluids can move among compartments

  18. Protein Function • Edema occurs when there are inadequate plasma proteins • This occurs when: • Liver disease • Inadequate protein/food intake • Kidney disease  blood proteins excreted • Injury breaks open cells

  19. Protein Function • Acid Base Balance • Proteins can act as acids and bases • Help keep body fluids at a safe pH • Serve as buffers in the body

  20. Protein Function • Energy • 4 kcal/gram • Use as a source of energy when glucose/glycogen stores are empty

  21. Amino Acids • The body regularly breaks down proteins and remakes them or uses them for energy as needed – see page 199 • If an essential a.a. is missing the body cannot make all of the proteins it needs • Hair and nails may grow more slowly • Immune system compromised (antibodies are proteins)

  22. Nitrogen Balance • Positive Nitrogen Balance • Making more protein than breaking down • Anabolism > catabolism • Pregnant women • Infants and children • Athletes (building muscle) • Recovering from surgery, injury, or illness

  23. Nitrogen Balance • Negative Nitrogen Balance • Breaking down more protein than you are making • Catabolism > anabolism • Illness, fever • Burn victims • Starvation/anorexia

  24. Nitrogen Balance • In Zero Nitrogen Balance • Protein made = protein broken down • Anabolism = catabolism • Most adults are in zero nitrogen balance

  25. Protein in the Diet • Complete Proteins • Contain all 9 essential a.a. in adequate amounts • Food Sources • Most animal sources of protein are complete proteins (exception is gelatin) • Meat, poultry, fish, eggs, dairy • Soy products (plant source of complete protein)

  26. Protein in the Diet • Incomplete Proteins • Lack or are low in 1 or more of the essential a.a. • Food Sources • Most plant sources are incomplete proteins • Nuts, seeds, legumes, grains, and vegetables • Page 188 • Gelatin

  27. Protein in the Diet • Complementary Proteins • Two or more protein sources that together provide all 9 of the essential a.a. • Most combinations of at least 2 categories of plant proteins will complement each other • Seeds and nuts (with legumes) • Grains (with legumes) • Legumes (with seeds, nuts, grains) • Vegetables (with grains, nuts, seeds)

  28. © 2008 Thomson - Wadsworth

  29. Protein in the Diet • Examples of meals/foods containing complementary proteins: • Rice and beans • …..

  30. Protein Digestion • Digestion • Mouth • Stomach • Protein is denatured by hydrochloric acid. • Pepsinogen is converted into its active form pepsin by hydrochloric acid. • Pepsin chemically breaks proteins into smaller polypeptides

  31. Protein Digestion • In the Small Intestine • Pancreatic enzymes (proteases) digest protein into short peptide chains called oligopeptides, which contain four to nine amino acids. • SI enzymes (peptidases) split proteins into amino acids.

  32. Protein Absorption • Amino acids are absorbed into the cells of the SI and enter the blood • Amino acids are transported to the liver for processing

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