Proteins and Amino Acids

1. Chapter 6 Proteins and Amino Acids Chapter 6 Photo courtesy of the USDA

2. Amino Acids Are the Building Blocks of Protein • Proteins are sequences of amino acid • Compounds composed of carbon, hydrogen, oxygen, and nitrogen arranged as strands of amino acids • Types of amino acids • Essential: most come from diet • Nonessential: can be made in the body

3. Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Threonine Tryptophan Valine Alanine Arginine Asparagine Aspartic acid Cysteine Glutamic acid Glutamine Glycine Proline Serine Tyrosine Amino AcidsEssential & Non Essential Amino Acids

4. Proteins in the Body • Some are working molecules • Enzymes • Antibodies • Transport vehicles • Hormones • Cellular “pumps” • Oxygen carriers • Some are structural molecules • Tendons • Ligaments • Scars • Fibers of muscles • Cores of bone and teeth • Filaments of hair • Materials of nails

5. Amino Acids The building blocks of protein • Each amino acid has an amine group at one end • The nitrogen-containing part • An acid group at the other end • A distinctive side chain attached to the carbon at the center • Sequence of amino acids determines shape • Shape of protein determines function

7. The Variety of Proteins Hemoglobin • Large, globular protein • Packed into red blood cells • Carries oxygen • Made of 4 protein strands • Each strand holding an iron atom

9. The Variety of Proteins • Inherited Amino Acid Sequences • For each protein there exists a standard amino acid sequence • A sequence specified by heredity (genes) • If a wrong amino acid is inserted, health can be affected as in Sickle Cell Anemia • Normal hemoglobin contains two kinds of protein strands • In sickle-cell disease on one of the two strands, the protein is altered so that it is unable to carry oxygen

11. The Variety of Proteins • Sickle-cell disease • Red blood cells collapse from the normal disk shape into crescent shapes • If too many of these types of red blood cells appear in the blood the results are • Abnormal blood clotting • Strokes • Severe pain • Susceptibility to infection • Early death

12. The Variety of Proteins • Inherited Amino Acid Sequences • Genes determine the sequence of amino acids for each protein • Your unique combination of genes directs the making of all your body’s proteins The nucleus of body cells contains the DNA for making every human protein • Each cell does not make every protein • Cells specialize in making certain proteins typical of their cell types • Example-- Pancreas makes enzymes and hormones

13. The Variety of ProteinsDigestion and Absorption • Denaturing of Proteins Irreversible changes in a protein’s shape • caused by • Heat • Acids • Bases • Alcohols • Example: Digestion of food protein Stomach acids open up a protein’s structure • Allows digestive enzymes to make contact with the peptide bonds

14. The Variety of Proteins • Cooking denatures proteins • Changes that occur to an egg white when an egg is cooked • With regard to diet this is important because • A protein that binds both biotin and iron is denatured, liberating them for digestion

15. Protein Digestion • When eating a protein source the body must break it down into amino acids • These amino acids can then be arranged into human body proteins • Mouth • Protein is crushed by chewing and moistened with saliva • Stomach • Acid (1.5 pH) uncoils protein’s strands so the stomach’s protein-digesting enzyme can attack the peptide bonds • These enzyme works best in an acidic environment • The stomach lining is protected from the acid and enzymes by a mucus coating secreted by stomach cells

16. Protein Digestion • Small intestine • Receives small denatured pieces of protein • Alkaline juices from the pancreas neutralize the acid • The pH increases to about 7 (neutral) • Protein-digesting enzymes from the pancreas and small intestine continue breaking down protein until all that is left are dipeptides, tripeptides, or single amino acids • Cells along the small intestine absorb single amino acids

18. After Protein Is Digested, What Happens…? • Amino acids are absorbed into the bloodstream • Carried to the liver • Used by the liver or released into the blood to be taken up by other cells • Cells can then use the amino acids to • Make their proteins for their own use • Make proteins that are released into the lymph or blood for other uses • When necessary body cells can use amino acids for energy

19. The Roles of Proteins in the Body Amino acids are needed To build the proteins of new tissue • Embryo • Muscles of an athlete in training • Growing child • New blood to replace losses • Scar tissue • New hair and nails To replace • Worn-out cells and internal cell structures • Red blood cells live only 3-4 months • Cells lining the intestinal tract live only 3 days • Skin cells are constantly being shed and replaced

20. Role of Proteins • Enzymes • Thousands of enzymes live inside a single cell • Each is a catalyst that facilitates a specific chemical reaction • Hormones • Chemical messengers that respond to conditions that require regulation • Each hormone affects a specific organ or tissue and elicits a specific response • Are made from amino acids and lipids

21. Role of Protein • Antibodies • Large proteins in the blood, produced by the immune system • Distinguish between “foreign” and “self” proteins • Inactivate foreign proteins. The next time the body encounters the same foreign protein, it destroys it even more rapidly

22. Role of Proteins Maintaining Fluid and Electrolyte Balance Failure of any part of the fluid balance system causes edema-- seen in protein deficiency Maintaining Acid-Base Balance Blood proteins act as buffers to maintain the blood’s normal pH not too acid and not to basic ( pH 7) Acidosis and alkalosis can denature proteins causing coma or death by denaturing proteins

23. Role of Proteins • Energy • Proteins can provide energy • Many amino acids can be converted to glucose to serve the glucose needs of the brain

25. Role of ProteinsProviding Energy and Glucose • Glucose is stored as glycogen • Fat is stored as triglycerides • There is no specialized protein energy-storage compound • When protein-sparing energy from carbohydrate and fat is lacking, the body must dismantle its tissue proteins (blood, muscle) to obtain amino acids for energy • Energy deficiency (starvation) can cause wasting of lean body tissue as well as loss of fat

26. Providing Energy and Glucose • If amino acids are over supplied, the body cannot store them • The body removes and excretes the amine groups-It is wasted • The residue (C, H, O) can be • Converted to glucose for energy or • stored as glycogen or fat

27. The Fate of an Amino Acid • Wasting occurs when: • The body does not have enough energy from other sources • Has more protein than it needs • Has too much of any single amino acid • Such as from a supplement • Or the diet supplies protein of low quality, with too few essential amino acids

28. The Fate of an Amino Acid • To prevent the wasting of dietary protein and permit the synthesis of needed body protein • Dietary protein must be adequate in quantity • The diet must supply all of the essential amino acids in the proper amounts • Enough energy-yielding carbohydrate and fat must be present to prevent the dietary protein from being wasted

29. Consumer Corner: Protein and Amino Acid Supplements Critically ill patients Supplemental amino acids may help reverse malnutrition in some critically ill patients Healthy people Protein supplements used as a replacement for food can be dangerous Especially when used in weight loss diets “Liquid protein” diets have caused deaths and heart problems in the past

30. Consumer Corner: Protein and Amino Acid Supplements • Lysine supplements • Touted to prevent or relieve the infections that cause herpes sores • Does not cure herpes infections • Unknown if it reduces outbreaks • Unknown if it is safe • Blends of amino acids leucine, isoleucine and valine • Popular with athletes hoping for a competitive edge • Value of these supplements is unclear

31. Consumer Corner: Protein and Amino Acid Supplements • Tryptophan supplements • Tryptophan is a precursor of the neurotransmitter serotonin • Advertised to relieve • Pain • Depression • Insomnia • DRI committee concludes that high doses of tryptophan may cause • Sleepiness • Severe nausea • Skin disorders

32. Protein and Amino Acid Supplements • People vulnerable to harm from protein supplements • Women of child-bearing age • Pregnant or lactating women • Infants, children, adolescents, and the elderly • People with inborn errors of metabolism that affect their bodies’ handling of amino acids

33. Protein and Amino Acid Supplements • DRI committee reviewed the available research on amino acid supplements • Not enough research exists to support long-term use of supplements by healthy people • More research into adverse effects is needed • Canada • Bans the sale of single amino acid supplements to consumers

34. Food Protein • Protein quality Determines how well a diet supports the growth of children and the health of adults Influenced by • A protein’s digestibility • A protein’s amino acid composition

35. Which Kinds of Protein-Rich Foods Are Easiest to Digest? • Digestibility of a protein varies from food to food • The amino acids from animal sources are more easily digested • Animal sources: 90+% digested and absorbed • Legumes: ≈80%-90% digested and absorbed • Grains and other plant foods:≈70%-90% digested and absorbed

36. Amino Acid Composition • High-quality proteins Dietary proteins containing all of the essential amino acids in relatively the same amounts that human beings require May also contain nonessential amino acids

37. Amino Acid Composition • Limiting Amino Acids • Is an essential amino acid present in dietary protein in a small amount • Thereby limiting the body’s ability to build protein • Lack of availability will slow protein synthesis • When the limiting amino acids are available again cells resume their normal protein synthesis

38. Amino Acid Composition • Complementary proteins • Mutual supplementation • The strategy of combining two incomplete proteins sources so that the amino acids in one food make up for those lacking in the other food

40. Amino Acid Composition

41. Amino Acid Composition • For people in areas where food sources are less reliable, protein quality can make the difference between health and disease • When food energy intake is limited or when the variety of foods is severely limited the primary food source of protein is important

42. Measuring Protein Quality • Protein digestibility-corrected amino acid score (PDCAAS) • A measuring tool used to determine protein quality • Reflects a protein’s digestibility as well as the proportions of amino acids that it provides

43. Measuring Protein Quality • 100 - 0 scale • 100: egg white, ground beef, tuna fish, etc. • Protein sources that are most readily digested and most perfectly balanced for meeting human needs. • 94: soybean • 60s-50s: most legumes • 25: wheat protein; gluten

44. How Much Protein Do People Need • DRI • Designed to cover the need to replace protein-containing tissue that healthy adults lose and wear out every day • Depends on body size: larger people have a higher protein need • For adults: 0.8g/kg body weight/day • Minimum: 10% of total calories • Athletes may need slightly more • Increased need is well covered by a regular diet

45. How Much Protein Do People Need • Nitrogen balance • The amount of nitrogen consumed is compared with the amount excreted in a given time period • Studies of nitrogen balance underlie the DRI Committee’s recommendations

47. How Much Protein Do People Need Positive nitrogen balance • Growing children add new blood, bone, and muscle cells to their bodies every day They have more protein, and more nitrogen, at the end of the day than the beginning • Same for a pregnant woman

48. How Much Protein Do People Need • Negative nitrogen balance • Occurs when muscle or other protein tissue breaks down and is lost • Illness or injury trigger the body to break down some of the less vital proteins • They provide amino acids and energy to help the body fight the illness

49. What Happens When People Consume Too Little Protein? • Protein-energy malnutrition (PEM) protein-calories malnutrition (PCM) • World’s most widespread malnutrition problem • Includes both marasmus and kwashiorkor and states in which they overlap

50. What Happens When People Consume Too Little Protein? • Marasmus • Chronic inadequate food intake • Inadequate energy, vitamins, minerals, and protein intake • Person is shriveled and lean all over • Kwashiorkor • Swollen belly and skin rash are present • Severe acute malnutrition • Too little protein to support body functions • Marasmus and kwashiorkor can occur in combination