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Chapter 25: Metabolism

Chapter 25: Metabolism. Introduction to Cellular Metabolism. Formation of Organic Molecules. Energy production begins in cytosol. Energy is captured to produce ATP. Figure 25–1. Energy. Large food molecules contain energy Energy in the form of chemical bonds

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Chapter 25: Metabolism

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  1. Chapter 25:Metabolism

  2. Introduction to Cellular Metabolism Formation of Organic Molecules Energy production begins in cytosol Energy is captured to produce ATP Figure 25–1

  3. Energy • Large food molecules contain energy • Energy in the form of chemical bonds • Work required to liberate energy • ATP: breaking the P bond provides energy for cells ATP ADP + P + free energy from food Food Energy + ADP + P  ATP (This ATP permits anabolism)

  4. Energy • Cells break down organic molecules to obtain energy: • used to generate ATP • Most energy production takes place in mitochondria

  5. Essential Materials • Oxygen • absorbed at the lungs • Water • Nutrients: absorbed at digestive tract • vitamins • mineral ions • organic substrates

  6. Materials Transport • Cardiovascular system: • carries materials through body • Materials diffuse: • from bloodstream into cells

  7. Metabolism • Refers to all chemical reactions in an organism • Includes all chemical reactions within cells • Provides energy to maintain homeostasis and perform essential functions

  8. Essential Metabolic Functions • Metabolic turnover: • periodic replacement of cell’s organic components • Growth and cell division • Special processes: • secretion • contraction • propagation of action potentials

  9. The Nutrient Pool • Contains all organic building blocks cell needs: • to provide energy • to create new cellular components • Is source of substrates for catabolism and anabolism • Catabolism: • Is the breakdown of organic substrates • Releases energy used to synthesize high-energy compounds (e.g., ATP) • Anabolism: • Is the synthesis of new organic molecules via forming new chemical bonds

  10. Nutrient Use in Cellular Metabolism Figure 25–2 (Navigator)

  11. Organic Compounds • Glycogen (carbohydrates) short carbon chains • most abundant storage carbohydrate • a branched chain of glucose molecules • Triglycerides fatty acids and glycerol • most abundant storage lipids • primarily of fatty acids • Proteins amino acids • most abundant organic components in body • perform many vital cellular functions

  12. KEY CONCEPT • There is an energy cost to staying alive • Even at rest cells must spend ATP to: • perform routine maintenance • remove and replace structures and components • Cells spend additional energy for vital functions: • growth • secretion • contraction

  13. Oxidation-Reduction Reactions (Redox Rxns) • Oxidation = the removal of electrons (Or addition of oxygen) • Reduction = the addition of electrons • These reactions are always coupled • One molecule must be oxidized while another is reduced A-e’ + B  A + B-e’ • Oxidized molecule (A): Loses energy OIL • Reduced molecule (B): Gains energy RIG

  14. Oxidation-Reduction Reactions (Redox Rxns) • Cells perform dehydrogenation reactions • Hydrogen (1 proton + 1 electron) is exchanged instead of a free electron, but this is still a redox reaction • Catabolism of large molecules result in reduced carrier compounds • e.i. ADP  ATP; NAD  NADH; FAD  FADH2 • These reduced compounds are later oxidized to generate ATP

  15. ATP Production • Requires the addition of a phosphate to ADP • Two Methods for ATP Productions • Substrate Level Phosphorylation - High energy phosphate is transferred directly from a substrate to ADP forming ATP • Oxidative Phosphorylation • Electrons are transferred from an organic compound to a cofactor carrier molecule (e.g. NAD+) • Electrons are passed through other carriers (the electron transport chain) to a final acceptor (oxygen) • The passing of electrons releases energy that is harvested to add a phosphate to ADP • Process is called chemiosmosis.

  16. What are the basic steps in glycolysis, the TCA cycle, and the electron transport system?

  17. Carbohydrate Catabolism (Metabolism) • Carbohydrates are the primary source of cellular energy for most organisms • Glucose is the most commonly used carbohydrate and will always be used first • Generates ATP and other high-energy compounds by breaking down carbohydrates: glucose + oxygen  carbon dioxide + water 

  18. Carbohydrate Catabolism (Metabolism) Two methods for ATP productions via catabolism of glucose • Cellular Respiration • Requires oxygen to serve as the final electron acceptor in a series of redox reactions • Generate ATP by oxidative phosphorylation • Most efficient method of ATP production • 1 glucose generates 36 ATP • Involves reaction performed inside the mitochondria

  19. Carbohydrate Catabolism (Metabolism) Two methods for ATP productions via catabolism of glucose 2. Fermentation Requires an organic molecule to serve as the final electron acceptor Can be done in the absence of oxygen ATP is synthesized using substrate level phosphorylation Less efficient, 1 glucose generates 2 ATP In humans, results in lactic acid

  20. Anaerobic Vs. Aerobic RespirationGlycolysis • Anaerobic reactions: Fermentation • Do not require oxygen • Example: Glycolysis • Breaks down glucose in cytosol: • into smaller molecules used by mitochondria • Aerobic reactions: Cellular Respiration • Occur in mitochondria: • consume oxygen • produce ATP

  21. Aerobic Respiration of GlucoseC6H12O6 + 6O2 6 CO2 + 6H2O Three Stages • Glycolysis • Oxidation of glucose to pyruvic acid • Some ATP and NADH produced • Citric Acid Cycle • Oxidation of acetyl to carbon dioxide • Some ATP, NADH and FADH produced • Electron Transport Chain • NADH and FADH2 are oxidized providing electrons for redox reactions • coenzymes that function to transport electrons in the form of hydrogen • Reduce oxygen to generate ATP • Majority of ATP is produced at this step

  22. Nutrient Use in Cellular Metabolism Figure 25–2 (Navigator)

  23. Glycolysis (Anaerobic Process) • Does not require oxygen • Occurs in cytoplasm • 10 step metabolic pathway: • Catabolizes and oxidizes one 6-carbon glucose molecule into two 3-carbon pyruvic acid molecules • Generates 2 ATP by substrate level phosphorylation • Many cells can survive on glycolysis alone • Not very efficient • Generates lactic acid as a waste product • Needs to be removed and processed to prevent • Drastic alterations in pH • Loss of homeostasis

  24. Glycolysis Factors • Glucose molecules • Cytoplasmic enzymes • ATP and ADP • Inorganic phosphates • NAD (coenzyme)

  25. Two Stages in Glycolysis • Preparatory Stage: • Enzyme phosphorylates last (sixth) carbon atom of glucose molecule: • Glucose-6-phosphate is formed using 1 ATP molecule - traps glucose molecule within cell • Fructose 1,6-bisphosphate is formed using 1 ATP • Therefore, two ATP molecules are used to phosphorylate one 6-carbon glucose and catabolize it into two 3-carbon molecules

  26. Two Stages in Glycolysis • Energy Conservation Stage: • the two 3-carbon molecules are oxidized to generate two 3-carbon pyruvic acid molecules • Two NAD+ molecules are reduced to two NADH molecules • 4 ATP molecules are produced by substrate level phosphorylation • net gain 2 ATP per 1 glucose

  27. Summary of Glycolysis 1 glucose + 2 NAD+ + 2 ADP + 2P  2 pyruvic acid + 2 NADH + 2H+ + 2 ATP

  28. Aerobic Reactions • If oxygen supplies are adequate: • mitochondria absorb and break down pyruvic acid molecules

  29. Mitochondrial Membranes • Outer membrane: • contains large-diameter pores • permeable to ions and small organic molecules (pyruvic acid) • Inner membrane: • contains carrier protein • moves pyruvic acid into mitochondrial matrix • Intermembrane space: • separates outer and inner membranes

  30. Mitochondrial ATP Production • H atoms of pyruvic acid: • are removed by coenzymes • are primary source of energy gain • C and O atoms: • are removed and released as CO2 • process of decarboxylation

  31. The TCA Cycle PLAY TCA Cycle Figure 25–4a (Navigator)

  32. Decarboxylation • Preparation of the Citric Acid Cycle • First step in aerobic process of glucose metabolism (oxygen is necessary) • 3 carbon pyruvic acid is decarboxylated into carbon dioxide and a 2 carbon acetyl • Acetyl is attached to coenzyme A (serves as a carrier) and one NAD+ is reduced to NADH • Occurs in the matrix of the mitochondria

  33. Summary of Decarboxylation 2 pyruvic acid + 2 NAD+ + 2 CoA  2 Acetyl CoA + 2 CO2 + 2 NADH

  34. Citric Acid Cycle • a.k.a. Kreb’s Cycle or Tricarboxylic Acid Cycle • Aerobic metabolism of glucose involves • 8 enzymatic reactions occurring in the mitochondrial matrix • Function to reduce the coenzyme NAD+ and FAD • 2-carbon acetyl + 4-carbon and 2 CO2 molecules • At the same time oxaloacetic acid  6-carbon citric acid • Oxidation and decarboxylation reactions: • Catabolize the 6-carbon citric acid back into a 4-carbon oxaloacetic acid • 3 NAD+ and 1 FAD are reduced into 3 NADH and 1 FADH2 • 1 ATP is produced by substrate level phosphorylation

  35. The TCA Cycle Figure 25–4b

  36. Citric Acid Cycle • Remember: • 1 glucose  2 pyruvic acid  2 acetyl so this cycle will run twice 2Acetyl Co A + 6NAD+ + 2FAD + 2ADP + 2P + 4H20  2CoA + 4CO2 + 6NADH + 4H+ + 2FADH2 + 2ATP

  37. Oxidative Phosphorylation Figure 25–5a (Navigator)

  38. Oxidative Phosphorylation Occurs on a membrane, the mitochondrial cristae, to generate most of the ATP produced from glucose Figure 25–5b

  39. Oxidative Phosphorylation • Is the most important mechanism for generation of ATP within the mitochondria • Produces more than 90% of ATP used by body • Requires oxygen, electrons, and coenzymes: • rate of ATP generation is limited by oxygen or electrons • Cells obtain oxygen by diffusion from extracellular fluid • Results in 2 H2 + O2 2 H2O

  40. The Electron Transport System (ETS) • Key reaction in oxidative phosphorylation • Is in inner mitochondrial membrane • Coenzymes from the previous reactions pass electrons (which transfer energy) to a series of electron carrier molecules • Molecules carry out redox reactions resulting in the chemiosmotic generation of ATP

  41. The Electron Transport System (ETS) • Three classes of carrier molecules • FMN (flavin mononucleotide): protein + flavin coenzyme • Coenzyme Q: nonprotein • Cytochromes: protein + an iron group - Most common

  42. Events of the Electron Transport Chain • NAD+ and FAD collected energy in the form of hydrogens (electrons) from organic molecules during Glycolysis, Decarboxylation, and the Citric Acid Cycle becoming that reduced forms NADH and FADH2 NAD+ + FAD  NADH + FADH2 • NADH and FADH2 are oxidized and pass hydrogens (electrons and protons) to the electron transport chain consisting of flavoproteins, cytochromes, and coenzyme Q. NADH + FADH2 NAD+ + FAD As electrons are passed along the chain, protons are pushed out through the membrane. This sets up a concentration gradient with protons (+ charge) on the outside and electrons (- charge) on the inside

  43. Events of the Electron Transport Chain • At the end of the chain the electrons are accepted by oxygen creating an anion (O-) inside, which has a strong affinity for the cations (H+) outside. • Chemiosmosis generates ATP: - H+ from the outside moves toward O- on the inside through special membrane channels that are coupled to ATP synthase - High-energy diffusion of H+ drives the reaction ADP + P  ATP. a. Energy from 1 NADH from glycolysis generate 2 ATP b. Energy from 1 NADH from decarboxylation and the citric acid cycle generate 3 ATP c. Energy from 1 FADH2 generate 2 ATP for a total of 32 ATP 5. H+ combines with O- inside the mitochondria creating water (H2O)

  44. Oxidative Phosphorylation Occurs on a membrane, the mitochondrial cristae, to generate most of the ATP produced from glucose Figure 25–5b

  45. Summary of Electron Transport 2 NADH from glycolysis + 2 NADH from decarboxylation + 6 NADH from Citric Acid Cycle + 2 FADH2 from Citric Acid Cycle + 6 O2 + 32 ATP + 32 P  12 H2O + 32 ATP + 10 NAD+ + 2 FAD

  46. Final Summary of Aerobic Respiration C6H12O6 + 6 O2 + 36 ADP + 36 P  6 CO2 + 6 H2O + 36 ATP 36 ATP: 2 from Glycolysis in cytoplasm 2 from Citric Acid Cycle by substrate level phosphorylation in matrix of mitochondria 32 from Electron Transport by oxidative phosphorylation in the cristae of the mitochondria

  47. Energy Yield of Aerobic Metabolism Figure 25–6

  48. Lipid Catabolism: Beta–Oxidation Figure 25–8 (Navigator)

  49. Lipolysis – Lipid Catabolism • Hydrolyzes triglycerides (fat storage)  glycerol and three fatty acids • Glycerol: • Glycerol  pyruvic acids in the cytoplasm • Pyruvic acid catabolized through TCA in mitochondria • Fatty Acids: • Fatty acids are catabolized by beta-oxidation into acetyl-CoA • In mitochondria to enter the TCA as two-carbon fragments • For each two-carbon fragment of fatty acid produced by beta-oxidation, the cell can generate 17 molecules of ATP • This is 1.5 times the energy production as with glucose • Generates more energy but requires more oxygen • Occurs much more slowly than equal carbohydrate metabolism

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