1. Chapter 9: Cellular Respiration
How Cells Make ATP:
Energy-Releasing Pathways

2. Summary:
Cellular respiration - the process by which your cells transfer the energy in organic compounds to ATP.
The byproduct of this reaction is water and carbon dioxide.
It occurs in the cells mitochondria, which are the energy producers for the cell.

3. Summary:
Each cell converts the energy in the chemical bonds of nutrients to chemical energy stored in ATP
May be aerobic or anaerobic
Most cells use aerobic respiration
3 pathways that are exergonic and release energy:
Aerobic respiration
Anaerobic respiration
Fermentation

4. Aerobic Respiration Most eukaryotes and prokaryotes Requires oxygen
To obtain energy from glucose
Requires oxygen
Nutrients are catabolized to CO2 and H2O
Glucose + Oxygen Carbon Dioxide + Water Energy (in bonds of ATP)

5. Aerobic Respiration A redox process
Glucose is oxidized to form Carbon Dioxide
Oxygen is reduced, forming water
The electrons produced are used to form ATP

6. Aerobic Respiration 3 stages: Glycolysis Citric Acid (Krebs) Cycle
Electron Transport Chain and Chemiosmosis

7. Aerobic Respiration
*In eukaryotes, glycolysis occurs in cytosol and remaining 2 steps occur in mitochondria.
* In bacteria, all stages occur in cytosol working with plasma membrane.

8. Mitochondrion Structure

9. Glycolysis Occurs in cytosol
Glucose converted to two 3-carbon molecules of pyruvic acid
ATP and NADH are formed
NADH - temporarily stores large amounts of free energy
Energy from NADH ultimately participates in reactions that form ATP
Net production of 2 ATP
Animation of Glycolysis

10. 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.

12. Citric Acid Cycle (Krebs Cycle)
Pyruvic Acid from Glycolysis moves into mitochondria.
Pyruvic acid breaks apart
1 molecule of CO2 is produced
2 other Carbon atoms form acetyl CoA
Acetyl CoA combines with 4 carbon molecules to produce citric acid.

13. Citric Acid Cycle (Krebs Cycle)
Citric Acid is broken down
CO2 released
Electrons transferred to energy carriers.
Carbon Dioxide is a waste product
ATP, NADH and FADH2 are produced
2 ATP are produced/glucose

15. Electron Transport Chain and Chemiosmosis
Electrons from Krebs cycle are passed to NADH and FADH2 in Electron Transport Chain
Enzymes present in mitochondrial membrane
As NADH and FADH2 pass along enzymes, they give up electrons (energy) = chemiosmosis
H+ ions are transported across membrane and come in contact with ATP synthase
ADP + Pi = ATP

17. End of chain – electrons combined with oxygen and hydrogen to form water
Via chemiosmosis, 34 ATP produced.
ATP synthesis continues until ADP stores are depleted

18. Equation
C6H12O6 + 6O2 -->6 CO2 + 6H2O + 38 ATP

19. Aerobic Respiration – End Results
One glucose gives maximum of ATP’s
Glycolysis produces 2 ATP molecules
2 ATP molecules are produced in the citric acid cycle
Remainder of ATP is produced in the electron transport system (32 or 34)
Efficiency is about 40%; remaining energy is disseminated as heat

20. Other nutrients (besides glucose) provide energy
More energy is gained from burning fats than glucose
Lipids contain 9 kcal/gram
Lipids are broken down and glycerol enters glycolysis
Fatty acids are converted to acetyl CoA and enter the citric acid cycle
Proteins are broken down to amino acids
Proteins contain 4 kcal/gram

21. Anaerobic Respiration and Fermentation do not Require Oxygen
Various inorganic substances serve as the final electron acceptor
Yield is only the 2 ATP molecules from glycolysis
Types of Fermentation
Alcohol
Lactate

22. Alcoholic Fermentation
Alcoholoic fermentation
Alcoholic fermentation produces ethanol
Pyruvate is converted to ethanol
Ethanol is a potentially toxic waste product
Yeast carry out alcoholic fermentation when oxygen deprived
Pyruvic acid + NADH -> alcohol + CO2 + NAD+

23. Lactate Fermentation
Bacteria and some fungi carry out lactate fermentation
Strenuous exercise in mammals results in lactate fermentation as well
Yields only the 2 ATP molecules from glycolysis
Pyruvic acid + NADH -> lactic acid + NAD+

24. Copyright Pearson Prentice Hall
Fermentation
Lactic acid fermentation converts glucose into lactic acid. The first part of the equation is glycolysis. The second part shows the conversion of pyruvic acid to lactic acid.
Copyright Pearson Prentice Hall