The Stages The Stages of Cellular of Cellular

RespirationRespiration9.2, 9.3, 9.4

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

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

Glycolysis

Actually a series of 10 reactions that occurNo oxygen is requiredNo CO2 is released

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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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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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+

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

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

Can you explain it?

• Where?• What goes in?• What is produced?

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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Can you explain it?

• Where?• What goes in?• What is produced?

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

The Citric Acid Cycle

For each turn of the cycle, 2 carbons enter on acetyl CoA, and 2 carbons leave as CO2

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

+ =

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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

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

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

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)

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

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

Chemiosmosis

• All throughout the inner membrane of the mitochondria are proteins called ATP synthase

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

Chemiosmosis

• So chemiosmosis = the energy from a hydrogen ion gradient is used to drive cellular work, such as the formation of ATP from ADP

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

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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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

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

Cellular Respiration Summary

• Cellular Respiration is ~ 40% efficient at storing energy from glucose in ATP

• Best efficiency on cars is 25%