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Cellular Respiration
Photo Credit: Duomo Photography, Inc.
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9-1 Chemical Pathways
Food serves as a source of raw materials for the cells in the body and as a source of energy.
Animal Cells
Animal
Mitochondrion
Plant
Photo Credits: left: ©Bob Gurr/DRK Photo; middle bottom: ©John Durham/Science Photo Library/Photo Researchers, Inc. ; middle top: ©Ron Boardman/Stone; right: ©Keith Porter/Photo Researchers, Inc.
Plant Cells
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Both plant and animal cells carry out the final stages of cellular respiration in the mitochondria.
Animal Cells
Outer membrane
Intermembrane space
Mitochondrion
Inner membrane
Photo Credits: left: ©Bob Gurr/DRK Photo; middle bottom: ©John Durham/Science Photo Library/Photo Researchers, Inc. ; middle top: ©Ron Boardman/Stone; right: ©Keith Porter/Photo Researchers, Inc.
Matrix
Plant Cells
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4. Chemical Energy and Food
One gram of the sugar glucose (C6H12O6), when burned in the presence of oxygen, releases 3811 calories of heat energy.
A calorie is the amount of energy needed to raise the temperature of 1 gram of water 1 degree Celsius.
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5. Overview of Cellular Respiration
What is cellular respiration?
Overview of Cellular Respiration
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6. Overview of Cellular Respiration
Electrons carried in NADH
Electrons carried
in NADH and
FADH2
Pyruvic acid
Glucose
Glycolysis
Cytoplasm
Mitochondrion
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7. Overview of Cellular Respiration
Cellular respiration is the process that releases energy by breaking down glucose and other food molecules in the presence of oxygen. 3 parts: Glycolysis Krebs Cycle Electron Transport Chain
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8. Overview of Cellular Respiration
The equation for cellular respiration is:
6O2 + C6H12O6 → 6CO2 + 6H2O + Energy
oxygen + glucose → carbon dioxide + water + Energy
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9. Overview of Cellular Respiration
Glycolysis takes place in the cytoplasm. The Krebs cycle and electron transport take place in the mitochondria.
Glycolysis
Cytoplasm
Mitochondrion
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What happens during the process of glycolysis?
Glycolysis
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Glycolysis
ATP Production
At the beginning of glycolysis, the cell uses up 2 molecules of ATP to start the reaction.
2 ATP
2 ADP
4 ADP
4 ATP
Glucose
2 Pyruvic
acid
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Glycolysis
When glycolysis is complete, 4 ATP molecules have been produced.
2 ATP
2 ADP
4 ADP
4 ATP
Glucose
2 Pyruvic
acid
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Glycolysis
This gives the cell a net gain of 2 ATP molecules.
2 ATP
2 ADP
4 ADP
4 ATP
Glucose
2 Pyruvic
acid
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Glycolysis
NADH Production
One reaction of glycolysis removes 4 high-energy electrons, passing them to an electron carrier called NAD+.
2 ATP
2 ADP
4 ADP
4 ATP
Glucose
2NAD+
2 Pyruvic
acid
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Glycolysis
Each NAD+ accepts a pair of high-energy electrons and becomes an NADH molecule.
2 ATP
2 ADP
4 ADP
4 ATP
Glucose
2NAD+
2 Pyruvic
acid 2
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The NADH molecule holds the electrons until they can be transferred to other molecules.
Glycolysis
2 ATP
2 ADP
4 ADP
4 ATP
2NAD+
2 Pyruvic
acid 2
To the electron transport chain
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The Advantages of Glycolysis
The process of glycolysis is so fast that cells can produce thousands of ATP molecules in a few milliseconds.
Glycolysis does not require oxygen.
Glycolysis
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18. 9-2 The Krebs Cycle and Electron Transport
Oxygen is required for the final steps of cellular respiration. Because the pathways of cellular respiration require oxygen, they are aerobic.
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What happens during the Krebs cycle?
The Krebs Cycle
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The Krebs Cycle
During the Krebs cycle, pyruvic acid is broken down into carbon dioxide in a series of energy-extracting reactions.
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The Krebs Cycle
The Krebs cycle begins when pyruvic acid produced by glycolysis enters the mitochondrion.
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The Krebs Cycle
One carbon molecule is removed, forming CO2, and electrons are removed, changing NAD+ to NADH.
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The Krebs Cycle
Coenzyme A joins the 2-carbon molecule, forming acetyl-CoA.
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The Krebs Cycle
Acetyl-CoA then adds the 2-carbon acetyl group to a 4-carbon compound, forming citric acid.
Citric acid
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Citric acid is broken down into a 5-carbon compound, then into a 4-carbon compound.
The Krebs Cycle
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The Krebs Cycle
Two more molecules of CO2 are released and electrons join NAD+ and FAD, forming NADH and FADH2
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The Krebs Cycle
In addition, one molecule of ATP is generated.
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The Krebs Cycle
The energy tally from 1 molecule of pyruvic acid is
4 NADH
1 FADH2
1 ATP
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How are high-energy electrons used by the electron transport chain?
Electron Transport
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Electron Transport The electron transport chain uses the high-energy electrons from the Krebs cycle to convert ADP into ATP.
Electron Transport
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Electron Transport
High-energy electrons from NADH and FADH2 are passed along the electron transport chain from one carrier protein to the next.
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Electron Transport
At the end of the chain, an enzyme combines these electrons with hydrogen ions and oxygen to form water.
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Electron Transport
As the final electron acceptor of the electron transport chain, oxygen gets rid of the low-energy electrons and hydrogen ions.
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Electron Transport
When 2 high-energy electrons move down the electron transport chain, their energy is used to move hydrogen ions (H+) across the membrane.
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Electron Transport
During electron transport, H+ ions build up in the intermembrane space, so it is positively charged.
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Electron Transport
The other side of the membrane, from which those H+ ions are taken, is now negatively charged.
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Electron Transport
The inner membranes of the mitochondria contain protein spheres called ATP synthases.
ATP synthase
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Electron Transport
As H+ ions escape through channels into these proteins, the ATP synthase spins.
Channel
ATP synthase
The electron transport chain uses high-energy electrons from the Krebs cycle to convert ADP to ATP.
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Electron Transport
As it rotates, the enzyme grabs a low-energy ADP, attaching a phosphate, forming high-energy ATP.
Channel
ATP synthase
The electron transport chain uses high-energy electrons from the Krebs cycle to convert ADP to ATP.
ATP
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The Totals
Glycolysis produces just 2 ATP molecules per molecule of glucose.
The complete breakdown of glucose through cellular respiration, including glycolysis, results in the production of 36 molecules of ATP.
The Totals
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The Totals
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42. Comparing Photosynthesis and Cellular Respiration
The energy flows in photosynthesis and cellular respiration take place in opposite directions.
Comparing Photosynthesis and Cellular Respiration
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43. Comparing Photosynthesis and Cellular Respiration
On a global level, photosynthesis and cellular respiration are also opposites.
Photosynthesis removes carbon dioxide from the atmosphere and cellular respiration puts it back.
Photosynthesis releases oxygen into the atmosphere and cellular respiration uses that oxygen to release energy from food.
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What happens when there is no oxygen present???
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Fermentation
When oxygen is not present, glycolysis is followed by a different pathway.
The combined process of this pathway and glycolysis is called fermentation.
Fermentation releases energy from food molecules by producing ATP in the absence of oxygen.
Fermentation
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46. Common Foods that use fermentation
Coffee
Chocolate
Tea
Sourdough bread
Cheese
Yogurt
Salami
Beer
Wine
Sauerkraut
Pickles
vinegar
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What are the two main types of fermentation?
Fermentation
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Alcoholic Fermentation
Yeasts and a few other microorganisms use alcoholic fermentation, forming ethyl alcohol and carbon dioxide as wastes.
The equation for alcoholic fermentation after glycolysis is:
pyruvic acid + NADH → alcohol + CO2 + NAD+
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Fermentation
Lactic Acid Fermentation
In many cells, pyruvic acid that accumulates as a result of glycolysis can be converted to lactic acid.
This type of fermentation is called lactic acid fermentation. It regenerates NAD+ so that glycolysis can continue.
The equation for lactic acid fermentation after glycolysis is:
pyruvic acid + NADH → lactic acid + NAD+
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Lactic acid build up in the muscles causes a burning sensation – caused by the lack of Oxygen
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