1. How Cells Harvest Energy Chapter 6
Cellular Respiration
How Cells Harvest Energy
Chapter 6

2. ATP Is Universal Energy Source
Photosynthetic organisms get energy from the sun
The light energy is converted to the chemical bond energy of ATP

3. Main Types of Energy-Releasing Pathways
Anaerobic pathways
Evolved first
Don’t require oxygen
Start with glycolysis in cytoplasm
Completed in cytoplasm
Aerobic pathways
Evolved later
Require oxygen
Start with glycolysis in cytoplasm
Completed in mitochondria

4. Redox reactions release energy when electrons “fall” from a hydrogen carrier to oxygen
NADH delivers electrons to a series of protein complexes in an electron transport chain
As electrons move from carrier to carrier, their energy is released in small quantities

5. Electron transport chain
In cellular respiration, electrons “fall” down an energy staircase and finally reduce O2
H2O
NAD+
NADH
ATP H+
Controlled release of energy for synthesis of ATP
Electron transport chain 2 O2 1
2e +

6. Main Pathways Start with Glycolysis
Glycolysis occurs in cytoplasm
Reactions are catalyzed by enzymes
Glucose 2 Pyruvate
(six carbons) (three carbons)

7. Glycolysis harvests chemical energy by oxidizing glucose to pyruvate

8. Net Energy Yield from Glycolysis
Energy investment phase:
2 ATP invested
Energy releasing phase:
2 NADH formed
4 ATP formed
Net yield: 2 ATP and 2 NADH

9. Pyruvate is chemically groomed for the Krebs cycle
Each molecule of pyruvate is broken down to form CO2 and acetyl co-A, which enters the Krebs cycle
Acetyl CoA (acetyl coenzyme A)
Pyruvic acid
CO2

10. The Krebs cycle completes the oxidation of glucose, generating many NADH and FADH2 molecules
Acetyl CoA
The Krebs cycle is a series of redox reactions in which enzymes strip away electrons and H+ 2
KREBS CYCLE
2 CO2

11. Oxidative phosphorylation powers most ATP production
The electrons from NADH and FADH2 travel down the electron transport chain to oxygen

12. Chemiosmosis powers most ATP production
Energy released by the electrons is used to pump H+ into the space between the mitochondrial membranes (intermembrane space) by active transport
In chemiosmosis, the H+ ions diffuse back through the inner membrane through ATP synthase , which capture the energy to synthesize ATP

13. Overview: Oxidative Phosphorylation
Occurs in the inner mitochondrial membrane
Coenzymes (NADH, FADH2) deliver electrons to electron transport systems
Electron transport sets up H+ ion gradients
Flow of H+ down concentration gradients powers ATP formation

14. Overview: Electron Transport System
Electron transport systems are embedded in inner mitochondrial compartment
NADH and FADH2 give up electrons that they picked up in earlier stages to electron transport system
Electrons are transported through the system
The final electron acceptor is oxygen

15. Summary of Aerobic Cellular Respiration
Glycolysis
2 ATP formed by substrate-level phosphorylation
Krebs cycle
ETC & Chemiosmosis (oxidative phosphorylation)
ATP formed
Total ATP molecules formed:

16. Anaerobic Pathways Do not use oxygen
Produce less ATP than aerobic pathways
Two types
Lactic acid fermentation
Alcoholic fermentation

17. Lactic Acid Fermentation
2 Lactate
NAD+
NADH 2
ATP
2 ADP + 2
2 Pyruvate
GLYCOLYSIS P
Glucose

18. Alcoholic Fermentation
NAD+
NADH 2
GLYCOLYSIS
2 ADP + 2 P
ATP
Glucose
2 Pyruvate
released
CO2
2 Ethanol