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AP Bio Ch. 9 part 2
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AP Bio Ch. 9 part 2



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  • 1. The Stages of Cellular Respiration 9.2, 9.3, 9.4
  • 2. The 3 Stages Stage 1 – Glycolysis – occurs in the cytosol Stage 2 – The Citric Acid Cycle (aka Kreb’s Cycle) – occurs in the matrix of the mitochondria Stage 3 – Oxidative phosphorylation – the electron transport chain and chemiosmosis – occurs in the cristae of the mitochondria
  • 3. Glycolysis • Glyco = sugar • Lysis = break Glycolysis is the first step This step occurs in the cytosol In this step, 6-carbon glucose is broken apart into two 3-carbon molecules called pyruvate
  • 4. Glycolysis Actually a series of 10 reactions that occur No oxygen is required No CO2 is released
  • 5. Glycolysis • Step 1 - the endergonic, energy investment phase – glucose is take in to cytosol – 2 ATP are used to “kick off” the reaction by phosphorylating the glucose – Once the 2 phosphate groups are attached at either end, the glucose molecule is ready to be split in ½
  • 6. Go to your diagram
  • 7. Glycolysis • Step 2 – the exergonic, energy payoff phase – The 3 carbon sugar is oxidized and NADH is formed • 2 Pyruvate molecules are what remains from the original glucose
  • 8. Go to your diagram
  • 9. Glycolysis Summary 1 glucose  2 pyruvate + 2 water 2 ATP used + 4 ATP formed  net gain of 2 ATP 2NAD+ + 4 e- + 4 H+ 2 NADH + 2 H+
  • 10. Aerobic Glycolysis • NAD+ gains a hydrogen and an electron and becomes NADH • NADH = an electron‑ carrier • Energy from 1 NADH is enough to make 3 ATP
  • 11. Glycolysis Summary • Glycolysis only released a small amount of the energy in glucose • Lots of energy still in the pyruvate molecules • If O2 is available, the pyruvate will enter the mitochondria and aerobic respiration will continue
  • 12. Can you explain it? • Where? • What goes in? • What is produced?
  • 13. Formation of Acetyl CoA, the linking step between glycolysis and the citric acid cycle • Pyruvate enters the mitochondria via active transport • One CO2 is broken off of the pyruvate • 2-carbon compound that remains is oxidized to form acetate, and the electron released is used to form NADH • Coenzyme A is attached to the acetate by an unstable bond to form acetyl CoA, which will enter the citric acid cycle
  • 14. Go to your diagram
  • 15. Can you explain it? • Where? • What goes in? • What is produced?
  • 16. The Citric Acid Cycle • 8 steps • Overall, from each molecule of pyruvate: – 3 CO2 released (1 from conversion of pyruvate to acetyl CoA, 2 from the citric acid cycle) – 4 NADH produced (1 from conversion of pyruvate to acetyl CoA, 3 from the citric acid cycle) – 1 FADH2 produced – 1 ATP produced
  • 17. The Citric Acid Cycle For each turn of the cycle, 2 carbons enter on acetyl CoA, and 2 carbons leave as CO2
  • 18. The Citric Acid Cycle • The acetyl group of acetyl CoA joins with oxaloacetate to form citrate (the ionized form of citric acid) + • The next steps break down citrate back to oxaloacetate Go to your diagram =
  • 19. The Citric Acid Cycle Summary • Each turn of the cycle produces 2 CO 2, 3 NADH, 1 FADH2, 1 ATP • So for 1 molecule of glucose, it would be 4 CO2, 6 NADH, 2 FADH2, and 2 ATP
  • 20. What do we have so far? For each molecule of glucose take in: • • • • 2 pyruvate 2 water glycolysis 2 ATP 2 NADH conversion of • 2 CO2 • 2 NADH • 4 CO2 • 6 NADH • 2 FADH2 • 2 ATP pyruvate to acetyl CoA Citric acid cycle • TOTAL energy yield so far: • 4 ATP • 10 NADH Powerful electron carriers that • 2 FADH2 will shuttle the electrons to the electron transport chain
  • 21. Oxidative Phosphorylation – the electron transport chain and chemiosmosis • Occurs in the inner membrane of the mitochondria – Inner membrane highly folded into cristae to make lots of surface area for lots of chemical reactions
  • 22. The Electron Transport Chain • Made up mostly of proteins in the mitochondrial membrane • Electrons delivered to the chain by NADH (delivers electrons to the top of the chain) and FADH2 (delivers electrons to a slightly lower step on the chain)
  • 23. The Electron Transport Chain • Electrons are shuttled down the chain from one electron carrier to the next • When the electron carrier accepts electrons, it is reduced • It then becomes oxidized when it passes those electrons to its neighbor lower down the chain, which is more electronegative and has a greater affinity for electrons
  • 24. The Electron Transport Chain Summary • No ATP produced directly from the electron transport chain • It functions in controlling the drop in free energy when electrons “fall” from glucose to oxygen • The released energy is then used to create ATP through chemiosmosis
  • 25. Chemiosmosis • All throughout the inner membrane of the mitochondria are proteins called ATP synthase
  • 26. Chemiosmosis • H+ ions accumulate during the electron transport chain • This creates an ion gradient across the membrane • This ion gradient provides the energy to drive the formation of ATP from ADP by the enzyme ATP synthase
  • 27. Chemiosmosis • So chemiosmosis = the energy from a hydrogen ion gradient is used to drive cellular work, such as the formation of ATP from ADP
  • 28. Chemiosmosis • As hydrogen ions flow down their gradient through the ATP synthase protein, parts of the protein spin, creating energy that phosphorylates ADP to make ATP
  • 29. Chemiosmosis • The hydrogen ion gradient is maintained by the electron transport chain • The electron transport chain uses the energy released from moving electrons down the chain to pump H+ across the membrane • This creates a proton-motive force- potential energy stored in the ion gradient • The hydrogen ions then move back down their gradient, through the only door open to them, ATP synthase
  • 30. Very slow animation  Go to your diagram
  • 31. Cellular Respiration Summary • 1 glucose molecule  30 ATP by NADH 4 ATP by FADH2 2 ATP by Citric Acid Cycle 2 ATP by Glycolysis Total 38 ATP
  • 32. Cellular Respiration Summary But…36-38 ATP is the actual total Slightly less because 1. Ratio of NADH to ATP not a whole number 2. ATP yield varies depending on electron carrier (FADH used more in brain, NADH used more in heart & liver) 3. Proton-motive force used to drive other reactions besides formation of ATP (like pulling in pyruvate
  • 33. Cellular Respiration Summary • Cellular Respiration is ~ 40% efficient at storing energy from glucose in ATP • Best efficiency on cars is 25%