Metabolism: Transformations & Interactions

1. Metabolism: Transformations & Interactions Chapter 7

2. Metabolism • Metabolism • The sum total of all the chemical reactions that go on in living cells • Energy Metabolism • Includes all the reactions by which the body obtains & spends energy from food

3. The Site of Metabolic Reactions • Metabolic reactions take place inside cells, especially liver cells • Anabolism is the building up of body compounds and requires energy. • Catabolism is the breakdown of body compounds and releases energy.

4. The Site of Metabolic Reactions

5. Energy Yielding Nutrients • From CHO →glucose • From fats → glycerol & FA • From proteins→ AA • 4 basic units used in metabolic pathway • Alcohol can disrupt normal metabolic pathways (Highlight 7)

7. The Transfer of Energy in Reactions - ATP • ATP – adenosine triphosphate • High-energy storage compound • Captures some energy released during breakdown of glucose, glycerol, fatty acids, and amino acids

8. Adenosine Triphosphate (ATP)

9. The Transfer of Energy in Reactions - ATP • Hydrolysis of ATP occurs simultaneously with reactions that will use that energy • Coupled reactions • Energy released from breakdown of one compound used to create bond in formation of another

11. Enzymes & Co-enzymes – Helpers in Metabolism • Co-enzymes are organic molecules that work with enzymes to facilitate their activity. • Enzymes & co-enzymes are helpers in metabolic reactions. • Some B vit serve as coenzymes to enzymes that release energy from glucose, glycerol, FA & AA.

12. Breaking Down Nutrients for Energy • Basic units enter metabolic pathways. During catabolism, the body separates atoms of basic units. • Glucose: 6 C • Glycerol: 3 C • FA: even number of C (commonly 16 or 18) • AA: 2, 3 or more C, with N attached • While each starts down a different path – 2 by-products are common • pyruvate & acetyl-coA • Eventually all enter the TCA cycle & electron transport chain

13. Glycolysis • Glucose splitting • 6-C Glucose → two 3-C compounds → Pyruvate Glucose anaerobic Pyruvate

15. If cell needs energy (& O2 is available), it removes COOH group from pyruvate to produce 2 C compounds that bonds with CoA to form Acetyl CoA Pyruvate Acetyl CoA Absence of sufficient O2 (or mitochondria) pyruvate is converted to lactic acid Pyruvate anaerobic Lactate Lactate recycled to glucose in liver by Cori cycle Pyruvate to Acetyl CoA aerobic

17. Paths of Pyruvate & Acetyl CoA

18. Glycerol to Pyruvate • 3-C glycerol is easily converted to pyruvate • Also easily converted to glucose Glucose Glycerol Pyruvate

19. Fatty Acids to Acetyl CoA • FA are taken apart in 2-C units through fatty acid oxidation. • 2-C units split off & combine with CoA to form Acetyl CoA. • If cell doesn’t need energy, acetyl CoA molecules combine to create TG.

21. Amino Acids Breakdown • Deaminated first (lose N) • Catabolized in a variety of ways: • Pyruvate  glucose • Acetyl CoA  more energy or body fat • Directly into TCA Cycle  generate energy

23. Amino Acids Breakdown • Amino Acids • Deamination results in two products: • Keto acid • Ammonia • Transamination is the transfer of the amino group from an amino acid to a keto acid. • Ammonia is converted to urea—a much less toxic compound—in the liver. • Urea is excreted through the kidneys to rid the body of unused nitrogen.

27. Breaking Down Nutrients for Energy • In Summary • Glucose and fatty acids are primarily used for energy, amino acids to a lesser extent. • Glucose is made from all carbohydrates, most amino acids and the glycerol portion of fat. • Protein is made from amino acids. • Glucose can be made into nonessential amino acids if nitrogen is present. • All energy-yielding nutrients consumed in excess can contribute to fat storage.

28. Breaking Down Nutrients for Energy – the final steps TCA Cycle – tricarboxylic acid cycle (aka Kreb’s cycle) • Oxaloacetate picks up acetyl CoA & drops off 2-C & returns to pick up another acetyl CoA. • As acetyl CoA breaks to CO2, H atoms with their electrons are removed. • Coenzymes made from B vitamins take H & electrons & transfers them to ETC.

30. Breaking Down Nutrients for Energy – the final steps Electron Transport Chain (ETC) • Consist of a series of proteins that serve as electron carriers. These carriers are inside inner membrane of mitochondria. • In ETC, energy is captured in bonds of ATP molecules. • ATP leaves mitochondria & enters cytoplasm, where it can be used for energy.

32. Kcal/gram • Each ATP holds energy & Kcal measures energy, so the more ATP generated the more Kcal collected. • One glucose molecule yield 36-38 ATP when oxidized completely. • One 16 carbon FA yield 129 ATP when oxidized completely.

34. Energy Balance - Surplus • When energy intake exceeds energy output, there is a gain in weight. • Fat cells enlarge & multiply regardless of whether the excess comes from protein, CHO or fat. • Most direct & efficient pathway to body fat is dietary fat.

35. Energy Balance • Body needs energy all the time • Relies on energy stores between meals • glycogen • fatty acids • lean mass tissue .. least preferred

36. Energy Balance – Fasting/Starvation • Fasting—Inadequate Energy • Glucose needed for the brain • Protein meets glucose needs • The shift to ketosis • Ketones are produces when glucose is not available. • Ketosis causes a suppression of the appetite. • Slowing of metabolism

37. Energy Balance – Fasting/Starvation • Fasting—Inadequate Energy • Symptoms of starvation • Muscle wasting • Decreased heart rate, respiratory rate, metabolic rate, and body temperature • Impaired vision • Organ failure • Decreased immunity • Depression, anxiety, and food-related dreams

39. Alcohol & Nutrition

40. Alcohol • For most adults, moderate consumption of alcohol is no more than 1 drink a day & no more than 7 drinks a week. • Pregnant women are advised to avoid alcohol.

41. Alcohol in body • Doesn’t need digestion & quickly absorbed. • About 20% is absorbed directly across walls of an empty stomach & can reach brain within minutes. • Stomach breaks down alcohol with its alcohol dehydrogenase enzyme. • Can reduce amount of alcohol entering blood by about 20%.

42. Alcohol in small intestine • Rapidly absorbed • From then on, it’s absorbed & metabolized before most nutrients which ensures a speedy disposal.

43. Alcohol in liver • Liver cells make alcohol dehydrogenase enzyme to oxidize alcohol. • It can process about ½ ounce of ethanol per hour • Rate is set by amount of alcohol dehydrogenase available. • Extra alcohol circulates until liver enzymes are available to process it.

44. Liver deterioration • 1st stage – fatty liver • 2nd stage – fibrosis • 3rd stage – cirrhosis (damage least reversible)

46. Alcohol Metabolism Fat (triglycerides) Fatty acids NAD+ NADH + H+ NAD+ NADH + H+ Alcohol (ethanol) Acetyl CoA Acetaldehyde Acetate Alcohol dehydrogenase Acetaldehyde dehydrogenase CoA TCA Cycle Acetyl CoA molecules are blocked from getting into the TCA cycle by the high level of NADH. Instead of being used for energy, the acetyl CoA molecules become building blocks for fatty acids. Fig. H7-3, p. 241

47. Alcohol & Metabolism • Alcohol alters amino acid & protein metabolism • Synthesis of protein important to immune system slows down, weakening body’s defense against infection. • Protein deficiency can develop.

48. Alcohol Effects Fig. H7-4, p. 242

49. Alcohol Effects • Alcohol reduces production of Anti-diuretic hormone which retains H2O. • Drinking alcoholic beverages – ↑ water loss - leads to dehydration.

50. Alcohol Effects • Alcohol can contribute to body fat promote obesity. • High in calories • Most often associated with central obesity • More Kcal from alcohol - fewer Kcal from nutritious food