Understanding Proteins: Chemistry, Structure, and Metabolism

1. Protein: Amino Acids Chapter 6

2. The Chemist’s View of Proteins • Atoms • Carbon, hydrogen, oxygen, nitrogen • Amino acids • Carbon • Hydrogen • Amino group • Acid group • Side group or side chain

3. The Chemist’s View of Proteins • More complex than carbohydrates or fats • Twenty amino acids (AA) • Different characteristics • Essential amino acids • Nonessential amino acids • Conditionally essential

4. Amino Acids

5. Examples of Amino Acids

6. The Chemist’s View of Proteins • Proteins • Peptide bonds link amino acids • Condensation reactions • Amino acid sequencing • Primary structure – chemical bonds • Secondary structure – electrical attractions • Tertiary structure – hydrophilic & hydrophobic • Quaternary structure – two or more polypeptides

7. Condensation of Two Amino Acids to Form a Dipeptide

8. Amino Acid Sequence of Human Insulin

9. The Structure of Hemoglobin

10. The Chemist’s View of Proteins • Protein • Denaturation • Disruption of stability • Uncoil and lose shape • Stomach acid

12. Protein Digestion • Protein in food ≠ muscle in body • Must be broken down and built back up Protein (long polypeptides)  Short polypeptides  Tripeptides and dipeptides  Amino acids

13. Protein Digestion • Mouth • Mostly mechanical • Stomach • Hydrochloric acid denatures proteins • Pepsinogen to pepsin • Small intestine • Hydrolysis reactions • Peptidase enzymes

14. Protein Digestion in the GI Tract Know these by name and function Be able to recognize these names, don’t need to know exact mechanism of action

15. Protein Absorption • Specific carriers transport into intestinal cells • Some amino acids used by intestinal cells • Unused amino acids transported to liver • Through bloodstream to liver • Reminder: enzymes are digested when they are inactive – different pH levels are optimal • Myth: predigested proteins are easier for the body to handle (i.e. better for you)

17. Protein Synthesis • Uniqueness of each person determined by differences in proteins • Uniqueness found in amino acid sequences • Determined by genes – DNA • Diet is key to protein synthesis • Adequate protein • Essential amino acids

19. Protein Synthesis • DNA transcription RNA translation protein • 2 Steps: • Transcription: DNA template makes mRNA • mRNA carries code across nuclear membrane to attach to ribosome • Ribosomes are protein factories • Translation: mRNA specifies AA sequence • tRNA carry AA to ribosomes

20. Sickle Cell Compared with Normal Red Blood Cell

21. Protein Synthesis • Gene expression and protein synthesis • Cells differentiate based on protein needs • Pancreas – insulin • RBC – hemoglobin • Dietary influence on gene expression • Protein and amino acids available to body • Disease development

22. Roles of Proteins • Structural materials • Building blocks for most body structures • Collagen: teeth, ligaments/tendons, arteries • Replacement of dead or damaged cells • Enzymes • Break down (digestion), build up (bone), and transform substances (gluconeogenesis) • Catalysts: remain unchanged, reusable

23. Enzyme Action

24. Roles of Proteins • Hormones • Messenger molecules • Transported in blood to target tissues • Regulators of fluid balance • Edema • Acid-base regulators • Attract hydrogen ions • Transporters – specificity

25. Examples of Hormones and Their Actions

26. An Example of Transport Protein

27. Roles of Proteins • Antibodies • Defend body against disease • Specificity • Immunity – memory • Energy and glucose • Starvation or insufficient carbohydrate intake • Other roles • Vision, blood clotting

28. Preview of Protein Metabolism • Protein turnover & amino acid pool • Constant production/destruction in each cell • Amino acid pool pattern is fairly constant • Used for protein production • Used for energy – if stripped of nitrogen • Nitrogen balance • Zero nitrogen balance • Positive and negative nitrogen balance

29. Preview of Protein Metabolism • Making other compounds (not just protein) • Neurotransmitters • Melanin • Thyroxin • Niacin • Energy and glucose • Wasting of lean body tissue • Adequate intake of carbohydrates and fats

30. Preview of Protein Metabolism • Making fat • Energy and protein exceed needs • Carbohydrate intake is adequate • Can contribute to weight gain • Deaminating amino acids • Stripped of amino group (N-containing) • Ammonia • Keto acid

31. Deamination and Synthesis of a Nonessential Amino Acid

32. Preview of Protein Metabolism • Make proteins & nonessential amino acids • Essential: breakdown of proteins • Nonessential: keto-acids • Liver makes nonessential • Converting ammonia to urea • Liver – ammonia and carbon dioxide •  Dietary protein ammonia production

33. Transamination and Synthesis of a Nonessential Amino Acid

34. Urea Synthesis

35. Preview of Protein Metabolism • Excreting urea • Liver releases urea into blood • Kidneys filter urea out of blood • Liver disease ( blood ammonia) • Kidney disease ( blood urea) • Protein intake and urea production • Water consumption

36. Urea Excretion

37. Protein Functions in the Body

39. Proteins in Food: Protein Quality • Two factors • Digestibility • Animal proteins (>90%) • Plant proteins (70-90%; soy, legumes >90%) • Amino acid composition • Essential amino acid consumption • Nitrogen-containing amino groups • Limiting amino acid

40. Protein Quality • Reference protein • Preschool-age children • High-quality proteins • Animal proteins • Plant proteins • Complementary proteins • Low-quality proteins combined to provide adequate levels of essential amino acids

41. Complementary Proteins

43. Health Effects of Protein • Protein deficiency • Consequences • Protein-energy malnutrition • Marasmus and kwashiorkor • Heart disease • Animal-protein intake • Homocysteine levels • Arginine levels

44. Health Effects of Protein • Cancer • Protein-rich foods; not protein content of diet • Osteoporosis • Increase in calcium excretion • Animal proteins • Weight control • Kidney disease • Acceleration of kidney deterioration

45. Recommended Intakes of Protein • Need for dietary protein • Source of essential amino acids • Practical source of nitrogen • AMDR: 10-35% of daily kcalorie • RDA: adults = 0.8g / kg of body weight • Groups with higher recommended intakes • Assumptions • Adequate energy

46. From Guidelines to Groceries • Protein foods • One ounce equals 7 grams of protein • USDA Food Patterns • Recommended sources • Milk and milk products • Fruits, vegetables, and grains • Read food labels • Current US and Canada intakes • Moderation

47. Protein and Amino Acid Supplements • Protein powders • Muscle work vs. protein supplements • Whey protein • Amino acid supplements • Potential risks associated with intake • Branched-chain amino acids (BCAA) • Lysine & tryptophan