Download - AP Bio Ch. 9 part 2
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The Stages The Stages of Cellular of Cellular
RespirationRespiration9.2, 9.3, 9.4
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The 3 StagesStage 1 –
GlycolysisGlycolysis – occurs in the cytosol
Stage 2 – The The Citric Acid Citric Acid CycleCycle (aka Kreb’s Cycle) – occurs in the matrix of the mitochondria
Stage 3 – Oxidative Oxidative phosphorylationphosphorylation – the electron transport chain and chemiosmosis – occurs in the cristae of the mitochondria
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Glycolysis
• Glyco = sugar• Lysis = breakGlycolysis is the first stepThis step occurs in the cytosol In this step, 6-carbon glucose is broken apart
into two 3-carbon molecules called pyruvate
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Glycolysis
Actually a series of 10 reactions that occurNo oxygen is requiredNo CO2 is released
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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
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Go to your diagram
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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
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Go to your diagram
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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+
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Aerobic Glycolysis
• NAD+ gains a hydrogen and an electron and becomes NADH
• NADH = an NADH = an electron‑carrierelectron‑carrier• Energy from 1 NADH is enough to make 3
ATP
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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
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Can you explain it?
• Where?• What goes in?• What is produced?
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Formation of Acetyl CoA, the linking step Formation of Acetyl CoA, the linking step between glycolysis and the citric acid cyclebetween 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
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Go to your diagram
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Can you explain it?
• Where?• What goes in?• What is produced?
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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
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The Citric Acid Cycle
For each turn of the cycle, 2 carbons enter on acetyl CoA, and 2 carbons leave as CO2
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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
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The Citric Acid Cycle Summary
• Each turn of the cycle produces 2 CO2, 3 NADH, 1 FADH2, 1 ATP
• So for 1 molecule of glucose, it would be 4 CO2, 6 NADH, 2 FADH2, and 2 ATP
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What do we have so far? For each molecule of glucose take in:
• 2 pyruvate• 2 water• 2 ATP• 2 NADH• 2 CO2
• 2 NADH• 4 CO2
• 6 NADH• 2 FADH2
• 2 ATP
• TOTAL energy yield so far:
• 4 ATP• 10 NADH• 2 FADH2
glycolysis
conversion of pyruvate to acetyl CoA
Citric acid cycle
Powerful electron carriers that will shuttle the electrons to the electron transport chain
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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
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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)
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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
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The Electron Transport Chain Summary
• No ATPNo 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
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Chemiosmosis
• All throughout the inner membrane of the mitochondria are proteins called ATP synthase
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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
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Chemiosmosis
• So chemiosmosis = the energy from a hydrogen ion gradient is used to drive cellular work, such as the formation of ATP from ADP
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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
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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
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Very slow animation Very slow animation Go to your diagram
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Cellular Respiration Summary
• 1 glucose molecule 30 ATP by NADH4 ATP by FADH2
2 ATP by Citric Acid Cycle
2 ATP by Glycolysis
Total 38 ATP
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Cellular Respiration Summary
But…36-38 ATP is the actual total Slightly less because 1. Ratio of NADH to ATP not a whole number2. 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
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Cellular Respiration Summary
• Cellular Respiration is ~ 40% efficient at storing energy from glucose in ATP
• Best efficiency on cars is 25%
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