1. Chapter 7 How Cells Release Chemical Energy (Sections 7.1 - 7.4)

2. 7.1 When Mitochondria Spin Their Wheels
Mitochondria produce ATP (high-energy molecule used by cells) by a process known as aerobic respiration
Electron transfer chains in mitochondrial membranes set up H+ gradients (remember this?) that power ATP formation

3. The Mitochondrion
Mitochondria have an internal folded membrane system that allows them to make ATP

4. 7.2 Extracting Energy From Carbohydrates
Most organisms convert chemical energy of carbohydrates (sugars) to chemical energy of ATP
Anaerobic (without oxygen) and aerobic (with oxygen) pathways of carbohydrate breakdown start in the cytoplasm with glycolysis, which converts glucose and other sugars to pyruvate
Not much ATP
Anaerobic fermentation pathways end in cytoplasm and yield two ATP per molecule of glucose

5. Key Terms anaerobic Occurring in the absence of oxygen aerobic
Involving or occurring in the presence of oxygen

6. Key Terms
glycolysis
Set of reactions in which glucose or another sugar is broken down to 2 pyruvate for a net yield of 2 ATP (not many ATP)
pyruvate
Three-carbon end-product of glycolysis
fermentation (oxygen not needed)
An anaerobic pathway by which cells harvest energy from carbohydrates to produce ATP

7. Evolution of Earth’s Atmosphere
The first cells on Earth did not use sunlight for energy
Ancient organisms extracted energy and carbon from simple molecules such as methane and hydrogen sulfide—gases that were plentiful in Earth’s early atmosphere
They used chemical energy from bonds in molecules already on the earth. They did not use the sun’s energy like plants today.

8. Evolution of Earth’s Atmosphere
Aerobic respiration, which uses oxygen and yields much more ATP than fermentation, evolved after O2 released by early photoautotrophs changed Earth’s atmosphere
aerobic respiration
Oxygen-requiring pathway that breaks down carbohydrates to produce ATP
photoautotroph
Photosynthetic autotroph

9. Then and Now
Artist’s conception of how Earth was permanently altered by the evolution of photosynthesis and aerobic respiration

10. C6H12O6 (glucose) + O2 (oxygen) → CO2 (carbon dioxide) + H2O (water)
Aerobic Respiration
This equation summarizes aerobic respiration:
C6H12O6 (glucose) + O2 (oxygen) →
CO2 (carbon dioxide) + H2O (water)
Note that aerobic respiration requires oxygen (a product of photosynthesis), and produces carbon dioxide and water (the raw materials of photosynthesis)

11. Energy, Photosynthesis, and Respiration
The connection between photosynthesis and aerobic respiration
Note the cycling of materials, and one-way flow of energy

12. Energy, Photosynthesis, and Respiration
CO2
glucose
H2O O2
Figure 7.3 The connection between photosynthesis and aerobic respiration. Note the cycling of materials, and the one-way flow of energy (compare Figure 5.5).
Aerobic Respiration
energy
Fig, 7.3, p. 108

13. Animation: Links with Photosynthesis

14. Carbohydrate Breakdown Pathways
Both fermentation and aerobic respiration begin in the cytoplasm with glycolysis
After glycolysis, pathways of fermentation and aerobic respiration diverge:
Aerobic respiration continues inside mitochondria, and ends when oxygen accepts electrons at the end of electron transfer chains
Fermentation ends in the cytoplasm, where a molecule other than oxygen accepts electrons

15. Overview: Aerobic Respiration

16. Aerobic Respiration In the Cytoplasm
A The first stage, glycolysis, occurs in the cell’s cytoplasm. Enzymes convert a glucose molecule to 2 pyruvate for a net yield of 2 ATP. 2 NAD+ combine with electrons and hydrogen ions during the reactions, so 2 NADH also form.
In the Mitochondrion
B The second stage occurs in mitochondria. The 2 pyruvate are converted to a molecule that enters the Krebs cycle. CO2 forms and leaves the cell. 2 ATP, 8 NADH, and 2 FADH2 form during the reactions.
C The third and final stage, electron transfer phosphorylation, occurs inside mitochondria. 10 NADH and 2 FADH2 give up electrons and hydrogen ions to electron transfer chains. Electron flow through the chains sets up hydrogen oxygen ion gradients that drive ATP formation. Oxygen accepts electrons at the end of the chains.
Figure 7.4 Overview of aerobic respiration. The reactions start in the cytoplasm and end in mitochondria.
Fig, 7.4, p. 109

17. Animation: Overview of Aerobic Respiration

18. Key Concepts Energy From Carbohydrates
Various pathways convert chemical energy of glucose and other organic compounds to chemical energy of ATP
Aerobic respiration yields the most ATP from each glucose molecule
In eukaryotes, this pathway ends in mitochondria

19. Animation: Where Pathways Start and Finish

20. Key Concepts Glycolysis
Glycolysis, the first stage of aerobic respiration and of anaerobic fermentation pathways, occurs in cytoplasm
Enzymes of glycolysis convert one molecule of glucose to two molecules of pyruvate for a net yield of two ATP