9-2 Continues9-2 Continues

Electron TransportElectron Transport

Electron Transport ChainElectron Transport Chain

The Krebs cycle generates high-energy The Krebs cycle generates high-energy electrons that are passed to NADH and electrons that are passed to NADH and FADHFADH22. .

The electrons are then passed from The electrons are then passed from those carriers to the those carriers to the electron transport chainelectron transport chain. .   

The electron transport chain uses the The electron transport chain uses the high-energy electrons from the Krebs high-energy electrons from the Krebs cycle to convert ADP into ATP. cycle to convert ADP into ATP.

Step A Electron TransportStep A Electron Transport

High-energy electrons from NADH and High-energy electrons from NADH and FADHFADH22 are passed along the electron are passed along the electron

transport chain. transport chain.

High-energy electrons are passed from High-energy electrons are passed from one carrier protein to the next. one carrier protein to the next.

Step A ContinuedStep A Continued

At the end of the electron transport At the end of the electron transport chain is an enzyme that combines these chain is an enzyme that combines these electrons with hydrogen ions and electrons with hydrogen ions and oxygen to form water.oxygen to form water.

Oxygen serves as the final electron Oxygen serves as the final electron acceptor of the electron transport chain.acceptor of the electron transport chain.

Thus, oxygen is essential for getting rid Thus, oxygen is essential for getting rid of low-energy electrons and hydrogen of low-energy electrons and hydrogen ions, the wastes of cellular respiration.ions, the wastes of cellular respiration.

Step B Hydrogen Ion MovementStep B Hydrogen Ion Movement Every time 2 high-energy electrons Every time 2 high-energy electrons

transport down the electron transport transport down the electron transport chain, their energy is used to transport chain, their energy is used to transport hydrogen ions (Hhydrogen ions (H++) across the ) across the membrane.membrane.

During electron transport, HDuring electron transport, H++ ions build ions build up in the intermembrane space, making up in the intermembrane space, making it positively charged. it positively charged.

The other side of the membrane, from The other side of the membrane, from which those Hwhich those H++ ions have been taken, is ions have been taken, is now negatively charged.now negatively charged.

Step C ATP ProductionStep C ATP Production

The inner membranes of the The inner membranes of the mitochondria contain protein spheres mitochondria contain protein spheres called ATP synthasescalled ATP synthases

As HAs H++ ions escape through channels ions escape through channels into these proteins, the ATP synthases into these proteins, the ATP synthases spin. spin.

Each time it rotates, the enzyme grabs Each time it rotates, the enzyme grabs a low-energy ADP and attaches a a low-energy ADP and attaches a phosphate, forming high-energy ATP.phosphate, forming high-energy ATP.

TOTALSTOTALS Recall that glycolysis produces just 2 Recall that glycolysis produces just 2

ATP molecules per glucose. ATP molecules per glucose.

The Krebs cycle and electron transport The Krebs cycle and electron transport enable the cell to produce 34 more ATP enable the cell to produce 34 more ATP molecules per glucose molecule, molecules per glucose molecule, in addition to the 2 ATP molecules in addition to the 2 ATP molecules

obtained from glycolysis. obtained from glycolysis.

18 times as much ATP can be 18 times as much ATP can be generated from glucose in the presence generated from glucose in the presence of oxygen. of oxygen.

The final wastes of cellular respiration The final wastes of cellular respiration are water and carbon dioxide.are water and carbon dioxide.

The 36 ATP molecules the cell makes The 36 ATP molecules the cell makes per glucose represent about 38 percent per glucose represent about 38 percent of the total energy of glucose. of the total energy of glucose.

The cell is actually more efficient at The cell is actually more efficient at using food than the engine of a typical using food than the engine of a typical automobile is at burning gasoline.automobile is at burning gasoline.

The remaining 62 percent is released as The remaining 62 percent is released as heat, which is one of the reasons your heat, which is one of the reasons your body feels warmer after vigorous body feels warmer after vigorous exercise.exercise.

Energy and ExerciseEnergy and Exercise

To obtain energy, To obtain energy, the body uses ATP the body uses ATP already in muscles already in muscles and new ATP made and new ATP made by lactic acid by lactic acid fermentation and fermentation and cellular respiration.cellular respiration.

Energy and ExerciseEnergy and Exercise

At the beginning of a At the beginning of a

race, the body uses race, the body uses all three ATP all three ATP sources, but stored sources, but stored ATP and lactic acid ATP and lactic acid fermentation can fermentation can only supply energy only supply energy for a limited time.for a limited time.

Quick EnergyQuick Energy Cells normally Cells normally

contain small contain small amounts of ATP amounts of ATP produced during produced during glycolysis and glycolysis and cellular cellular respiration.respiration.

Quick EnergyQuick Energy These sources can These sources can usually supply usually supply enough ATP to last enough ATP to last about 90 seconds. about 90 seconds. In a 200- or 300-In a 200- or 300-meter sprint, this meter sprint, this may be just enough may be just enough to reach the finish to reach the finish lineline

Fermentation produces lactic acid as a Fermentation produces lactic acid as a byproduct. byproduct.

When the race is over, the only way to When the race is over, the only way to get rid of lactic acid is in a chemical get rid of lactic acid is in a chemical pathway that requires extra oxygenpathway that requires extra oxygen. .

For that reason, you can think of a For that reason, you can think of a quick sprint building up an oxygen quick sprint building up an oxygen debt that a runner has to repay debt that a runner has to repay after the race with plenty of heavy after the race with plenty of heavy breathing.breathing.

Long Term EnergyLong Term Energy

For exercise longer than about 90 For exercise longer than about 90 seconds, cellular respiration is the only seconds, cellular respiration is the only way to generate a continuing supply of way to generate a continuing supply of ATP. ATP.

Cellular respiration releases energy Cellular respiration releases energy more slowly than fermentationmore slowly than fermentation

These stores of glycogen are usually These stores of glycogen are usually enough to last for 15 or 20 minutes of enough to last for 15 or 20 minutes of activity. activity.

After that, your body begins to break After that, your body begins to break down other stored molecules, including down other stored molecules, including fats, for energy.fats, for energy.

Comparing Photosynthesis and Comparing Photosynthesis and Cellular RespirationCellular Respiration

The energy flows in photosynthesis and The energy flows in photosynthesis and cellular respiration take place in cellular respiration take place in opposite directions. opposite directions.

Photosynthesis is the process that Photosynthesis is the process that “deposits” energy. “deposits” energy.

Cellular respiration is the process that Cellular respiration is the process that “withdraws” energy. “withdraws” energy.