Nutrition

1. Nutrition • Nutrient – a substance that promotes normal growth, maintenance, and repair • Major nutrients – carbohydrates, lipids, and proteins • Other nutrients – vitamins and minerals (and technically speaking, water)

2. USDA Food Guide Pyramid Figure 24.1a

3. Nutrition Figure 24.1b

4. Carbohydrates • Complex carbohydrates (starches) are found in bread, cereal, flour, pasta, nuts, and potatoes • Simple carbohydrates (sugars) are found in soft drinks, candy, fruit, and ice cream

5. Carbohydrates • Glucose is the molecule ultimately used by body cells to make ATP • Neurons and RBCs rely almost entirely upon glucose to supply their energy needs • Excess glucose is converted to glycogen or fat and stored

6. Carbohydrates • The minimum amount of carbohydrates needed to maintain adequate blood glucose levels is 100 grams per day • Starchy foods and milk have nutrients such as vitamins and minerals in addition to complex carbohydrates • Refined carbohydrate foods (candy and soft drinks) provide energy sources only and are referred to as “empty calories”

7. Lipids • The most abundant dietary lipids, triglycerides, are found in both animal and plant foods • Essential fatty acids – linoleic and linolenic acid, found in most vegetables, must be ingested • Dietary fats: • Help the body to absorb vitamins • Are a major energy fuel of hepatocytes and skeletal muscle • Are a component of myelin sheaths and all cell membranes

8. Lipids • Fatty deposits in adipose tissue provide: • A protective cushion around body organs • An insulating layer beneath the skin • An easy-to-store concentrated source of energy

9. Lipids • Prostaglandins function in: • Smooth muscle contraction • Control of blood pressure • Inflammation • Cholesterol stabilizes membranes and is a precursor of bile salts and steroid hormones

10. Lipids: Dietary Requirements • Higher for infants and children than for adults • The American Heart Association suggests that: • Fats should represent less than 30% of one’s total caloric intake • Saturated fats should be limited to 10% or less of one’s total fat intake • Daily cholesterol intake should not exceed 200 mg

11. Proteins • Complete proteins that meet all the body’s amino acid needs are found in eggs, milk, milk products, meat, and fish • Incomplete proteins are found in legumes, nuts, seeds, grains, and vegetables

12. Proteins • Proteins supply: • Essential amino acids, the building blocks for nonessential amino acids • Nitrogen for nonprotein nitrogen-containing substances • Daily intake should be approximately 0.8g/kg of body weight

13. Proteins: Synthesis and Hydrolysis • All-or-none rule • All amino acids needed must be present at the same time for protein synthesis to occur • Adequacy of caloric intake • Protein will be used as fuel if there is insufficient carbohydrate or fat available

14. Proteins: Synthesis and Hydrolysis • Nitrogen balance • The rate of protein synthesis equals the rate of breakdown and loss • Positive – synthesis exceeds breakdown (normal in children and tissue repair) • Negative – breakdown exceeds synthesis (e.g., stress, burns, infection, or injury) • Hormonal control • Anabolic hormones accelerate protein synthesis

15. Essential Amino Acids Figure 24.2

16. Vitamins • Organic compounds needed for growth and good health • They are crucial in helping the body use nutrients and often function as coenzymes • Only vitamins D, K, and B are synthesized in the body; all others must be ingested • Water-soluble vitamins (B-complex and C) are absorbed in the gastrointestinal tract • B12 additionally requires gastric intrinsic factor to be absorbed

17. Vitamins • Fat-soluble vitamins (A, D, E, and K) bind to ingested lipids and are absorbed with their digestion products • Vitamins A, C, and E also act in an antioxidant cascade

18. Minerals • Seven minerals are required in moderate amounts • Calcium, phosphorus, potassium, sulfur, sodium, chloride, and magnesium • Dozens are required in trace amounts • Minerals work with nutrients to ensure proper body functioning • Calcium, phosphorus, and magnesium salts harden bone

19. Minerals • Sodium and chloride help maintain normal osmolarity, water balance, and are essential in nerve and muscle function • Uptake and excretion must be balanced to prevent toxic overload

20. Metabolism • Metabolism – all chemical reactions necessary to maintain life • Cellular respiration – food fuels are broken down within cells and some of the energy is captured to produce ATP • Anabolic reactions – synthesis of larger molecules from smaller ones • Catabolic reactions – hydrolysis of complex structures into simpler ones

21. Metabolism • Enzymes shift the high-energy phosphate groups of ATP to other molecules • These phosphorylated molecules are activated to perform cellular functions

22. Stages of Metabolism • Energy-containing nutrients are processed in three major stages • Digestion – breakdown of food; nutrients are transported to tissues • Anabolism and formation of catabolic intermediates where nutrients are: • Built into lipids, proteins, and glycogen • Broken down by catabolic pathways to pyruvic acid and acetyl CoA • Oxidative breakdown – nutrients are catabolized to carbon dioxide, water, and ATP

23. Oxidation-Reduction (Redox) Reactions • Oxidation occurs via the gain of oxygen or the loss of hydrogen • Whenever one substance is oxidized, another substance is reduced • Oxidized substances lose energy • Reduced substances gain energy • Coenzymes act as hydrogen (or electron) acceptors • Two important coenzymes are nicotinamide adenine dinucleotide (NAD+)and flavin adenine dinucleotide (FAD)

24. Carbohydrate Metabolism • Since all carbohydrates are transformed into glucose, it is essentially glucose metabolism • Oxidation of glucose is shown by the overall reaction: • C6H12O6 + 6O2 6H2O + 6CO2 + 36 ATP + heat • Glucose is catabolized in three pathways • Glycolysis • Krebs cycle • The electron transport chain and oxidative phosphorylation

25. Glycolysis • A three-phase pathway in which: • Glucose is oxidized into pyruvic acid • NAD+ is reduced to NADH + H+ • ATP is synthesized by substrate-level phosphorylation • Pyruvic acid: • Moves on to the Krebs cycle in an aerobic pathway or • Is reduced to lactic acid in an anaerobic environment

26. Glycolysis Electron trans- port chain and oxidative phosphorylation Glycolysis Krebs cycle ATP ATP ATP Glucose Key: 2 ATP Phase 1 Sugar activation = Carbon atom Pi = Inorganic phosphate 2 ADP Fructose-1,6- bisphosphate P P Phase 2 Sugar cleavage Dihydroxyacetone phosphate Glyceraldehyde phosphate P P Pi 2 NAD+ 4 ADP 2 NADH+H+ 4 ATP Phase 3 Sugar oxidation and formation of ATP 2 Pyruvic acid 2 NADH+H+ O2 O2 2 NAD+ To Krebs cycle (aerobic pathway) 2 Lactic acid Figure 24.6

27. Krebs Cycle: Preparatory Step • Occurs in the mitochondrial matrix and is fueled by pyruvic acid and fatty acids

28. Krebs Cycle: Preparatory Step • Pyruvic acid is converted to acetyl CoA in three main steps: • Decarboxylation • Carbon is removed from pyruvic acid • Carbon dioxide is released

29. Krebs Cycle: Preparatory Step • Oxidation • Hydrogen atoms are removed from pyruvic acid • NAD+ is reduced to NADH + H+ • Formation of acetyl CoA – the resulting acetic acid is combined with coenzyme A, a sulfur-containing coenzyme, to form acetyl CoA

30. Krebs Cycle • An eight-step cycle in which each acetic acid is decarboxylated and oxidized, generating: • Three molecules of NADH + H+ • One molecule of FADH2 • Two molecules of CO2 • One molecule of ATP • For each molecule of glucose entering glycolysis, two molecules of acetyl CoA enter the Krebs cycle

31. Cytosol Pyruvic acid from glycolysis Electron transport chain and oxidative phosphorylation Glycolysis Krebs cycle NAD+ CO2 Mitochondrion (fluid matrix) NADH+H+ CoA Acetyl CoA ATP ATP ATP Oxaloacetic acid Citric acid (pickup molecule) NADH+H+ CoA (initial reactant) NAD+ Isocitric acid Malic acid NAD+ Krebs cycle CO2 NADH+H+ Fumaric acid a-Ketoglutaric acid CoA CO2 FADH2 NAD+ Succinic acid NADH+H+ Succinyl-CoA FAD Key: CoA = Carbon atom GDP + Pi GTP = Inorganic phosphate Pi = Coenzyme A CoA ATP ADP Figure 24.7

32. Electron Transport Chain • Food (glucose) is oxidized and the released hydrogens: • Are transported by coenzymes NADH and FADH2 • Enter a chain of proteins bound to metal atoms (cofactors) • Combine with molecular oxygen to form water • Release energy • The energy released is harnessed to attach inorganic phosphate groups (Pi) to ADP, making ATP by oxidative phosphorylation

33. Electron transport chain and oxidative phosphorylation Glycolysis Krebs cycle ATP ATP ATP H+ H+ H+ H+ Core Intermembrane space Cyt c e- e - Q 1 3 2 Inner mitochondrial membrane 1 2 O2 2 H+ + H2O FADH2 FAD ATP ADP + Pi NADH + H+ + NAD (carrying from food) e - H+ Mitochondrial matrix Electron Transport Chain ATP Synthase Figure 24.8

34. Electronic Energy Gradient • The electrochemical proton gradient across the inner membrane: • Creates a pH gradient • Generates a voltage gradient • These gradients cause H+ to flow back into the matrix via ATP synthase

35. ATP Synthase • The enzyme consists of three parts: a rotor, a knob, and a rod • Current created by H+ causes the rotor and rod to rotate • This rotation activates catalytic sites in the knob where ADP and Pi are combined to make ATP

36. Structure of ATP Synthase Figure 24.10

37. Summary of ATP Production Figure 24.11

38. Glycogenesis and Glycogenolysis • Glycogenesis – formation of glycogen when glucose supplies exceed cellular need for ATP synthesis • Glycogenolysis – breakdown of glycogen in response to low blood glucose Figure 24.12

39. Gluconeogenesis • The process of forming sugar from noncarbohydrate molecules • Takes place mainly in the liver • Protects the body, especially the brain, from the damaging effects of hypoglycemia by ensuring ATP synthesis can continue

40. Lipid Metabolism • Most products of fat metabolism are transported in lymph as chylomicrons: a large plasma lipoprotein particle, occurring as a droplet consisting primarily of triglycerides and functioning in the transport of neutral lipids from the intestine to the tissues by way of the lymph. • Lipids in chylomicrons are hydrolyzed by plasma enzymes and absorbed by cells • Only neutral fats are routinely oxidized for energy

41. Lipid Metabolism • Catabolism of fats involves two separate pathways • Glycerol pathway • Fatty acids pathway

42. Lipid Metabolism- Glycerol Pathway • Glycerol is converted to glyceraldehyde phosphate • Glyceraldehyde is ultimately converted into acetyl CoA • Acetyl CoA enters the Krebs cycle

43. Lipid Metabolism- Fatty Acids Pathway • Fatty acids undergo beta oxidation which produces: • Two-carbon acetic acid fragments, which enter the Krebs cycle • Reduced coenzymes, which enter the electron transport chain

44. Lipid Metabolism Figure 24.13

45. Lipogenesis and Lipolysis • Excess dietary glycerol and fatty acids undergo lipogenesis to form triglycerides • Glucose is easily converted into fat since acetyl CoA is: • An intermediate in glucose catabolism • The starting molecule for the synthesis of fatty acids

46. Lipogenesis and Lipolysis • Lipolysis, the breakdown of stored fat, is essentially lipogenesis in reverse • Oxaloacetic acid is necessary for the complete oxidation of fat • Without it, acetyl CoA is converted into ketones (ketogenesis)

47. Lipid Metabolism: Synthesis of Structural Materials • Phospholipids are important components of myelin and cell membranes

48. Lipid Metabolism: Synthesis of Structural Materials • The liver: • Synthesizes lipoproteins for transport of cholesterol and fats • Makes tissue factor, a clotting factor • Synthesizes cholesterol for acetyl CoA • Uses cholesterol to form bile salts • Certain endocrine organs use cholesterol to synthesize steroid hormones

49. Protein Metabolism • Excess dietary protein results in amino acids being: • Oxidized for energy • Converted into fat for storage • Amino acids must be deaminated prior to oxidation for energy

50. Protein Metabolism • Deaminated amino acids are converted into: • Pyruvic acid • One of the keto acid intermediates of the Krebs cycle • These events occur as transamination, oxidative deamination, and keto acid modification