AP Bio Ch. 9 part 2
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The document summarizes the three main stages of cellular respiration: glycolysis, the citric acid cycle, and oxidative phosphorylation. Glycolysis breaks down glucose in the cytosol, producing 2 pyruvate molecules, 2 ATP, and 2 NADH. The pyruvate then enters the mitochondria where the citric acid cycle generates carbon dioxide, NADH, FADH2, and 1 ATP per turn of the cycle. Finally, oxidative phosphorylation uses the electron transport chain and chemiosmosis to produce ATP from the NADH and FADH2, using the energy from electron transfers to pump hydrogen ions across the inner mitochondrial membrane and drive ATP synthase.
AP Bio Ch. 9 part 2
- 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
- 7. Go to your diagram
- 8. 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
- 10. 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+
- 11. 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
- 12. 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
- 13. Can you explain it? • Where? • What goes in? • What is produced?
- 14. 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
- 16. Can you explain it? • Where? • What goes in? • What is produced?
- 17. 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
- 18. The Citric Acid Cycle For each turn of the cycle, 2 carbons enter on acetyl CoA, and 2 carbons leave as CO2
- 19. 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 =
- 20. 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
- 21. 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
- 22. 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
- 23. 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)
- 25. 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
- 27. 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
- 29. Chemiosmosis • All throughout the inner membrane of the mitochondria are proteins called ATP synthase
- 30. 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
- 32. Chemiosmosis • So chemiosmosis = the energy from a hydrogen ion gradient is used to drive cellular work, such as the formation of ATP from ADP
- 33. 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
- 34. 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
- 35. Very slow animation Go to your diagram
- 37. 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
- 38. 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
- 39. Cellular Respiration Summary • Cellular Respiration is ~ 40% efficient at storing energy from glucose in ATP • Best efficiency on cars is 25%