THIRD STAGE OF AEROBIC RESPIRATION- A BIG ENERGY PAYOFF

Chapter 8.4

AP BiologyFall 2010

Electron Transfer Phosphorylation

Coenzymes donate electrons to electron transfer chains in the inner mitochondrial membrane

Flow of electrons through chains drives attachment of phosphate to ADP molecules

That is what electron transfer phosphorylation means

Electron Transfer Phosphorylation

Incremental energy release is more efficientTwo NADH that formed in the cytoplasm

(glycolysis) cannot directly reach the ATP forming machinery

Must give up electrons and hydrogen to transport proteins, which shuttle them across the inner membrane into the innermost compartment

NAD+ or FAD pick them up Eight NADH and two FADH2 from the second

stage are already inside

Electron Transfer Phosphorylation

Coenzymes turn over electrons to transfer chains

Coenzymes give up hydrogen, which now has a positive charge (H+)

Electrons lose a bit of energy through chainAt three transfers, that energy drives

pumping of H+ into the outer compartment H+ ions accumulate

Sets up concentration and electrical gradients across inner membrane

Electron Transfer Phosphorylation

H+ can’t cross lipid bilayerFollows its gradients by flowing through ATP

synthases ATP synthases changes shape, promotes

attachment of unbound phosphate to ADP forming ATP

Electron Transfer Phosphorylation

Last phase of electron transfer chain is passing electrons to oxygen Combines with H+ and forms water

Oxygen is final acceptor of electrons originally stripped from glucose

Electron Transfer Phosphorylation

Oxygen starved cells:Electrons have no where to go Chain backs up with electrons all the way to

NADPHNo H+ gradient forms, no ATP formsWithout oxygen, cell of complex organisms do

not survive long

Electron Transfer Phosphorylation: In Summary

NADH and FADH2 give up their electrons to transfer (enzyme) systems embedded in the mitochondrial inner membrane

The energy is used to pump hydrogen ions out of the inner compartment

When hydrogen ions flow back through the ATP synthases in the channels, the coupling of Pi to ADP yields ATP

Summing Up: The Energy Harvest

Electron transfer yields 32 ATPsGlycolysis yields 2 ATPsKrebs yields 2 ATPsTotal = 36 ATPs per glucose molecule

Anaerobic pathways may use up to 18 glucose molecules to get the same results

Summing Up: The Energy Harvest

Normally, for every NADH produced within the mitochondria and processed by the electron transfer chain Three ATP are formed FADH2 yields two ATPs

Summing Up: The Energy Harvest

In most cells (skeletal, brain), NADH from the cytoplasm cannot enter the mitochondrion and must transfer its electrons to FAD, yielding two ATP (for a total of 36)

However in the liver, heart, and kidney cells, NAD+ accepts the electrons to yield 3 ATP 2 NADH Produced per glucose giving total of 38 ATP

Cellular Respiration

Review

1. T/F Incremental energy releases energy less efficiently

2. T/F Electron transfer occurs along the cell membrane

3. T/F 32 ATPs are normally produced in the electron transport chain

Answer

1. False Incremental energy releases energy more efficiently

2. False Electron transfer occurs in the mitochondria (membrane)

3. True