1. Cellular Respiration Chapter 8

2. Cellular Respiration There are two pathways for cellular respiration.
Anaerobic Pathway-glycolysis and fermentation
Aerobic pathway-glycolysis paired with aerobic respiration in the mitochondria.
Carbohydrates produced in photosynthesis are converted into the energy of the cell, ATP.
Overall Equation:
C6H12O6 + 6O CO2 + 6H2O + energy (ATP)

3. Respiration is a Redox Reaction
Oxidation-reduction
LEO the lion says GER
Oxidation is e- loss
Reduction is e- gain
Reducing agent is the e- donor
Oxidizing agent is the e- acceptor

4. Oxidizing Agent in Respiration
NAD+
(nicotinamide adenine dinucleotide)
NAD+ is reduced to NADH
Enzyme action: dehydrogenase
Oxygen is the eventual e- acceptor

5. NAD+
Only a small amount of NAD+ is needed in cells; each NAD+ is used over and over.
Electrons received by NAD+ are high-energy electrons and are usually carried to the electron transport system.

6. FAD FAD coenzyme of oxidation-reduction can replace NAD+.
FAD accepts two electrons and becomes FADH2.

7. How Cells Acquire ATP Glucose is high-energy CO2 & H2O are low-energy
Process is exergonic and
releases energy.
Glucose is oxidized and
O2 is reduced.
Buildup of ATP is an endergonic rxn
that requires energy.
Breakdown of glucose yields
synthesis of 36 or 38 ATP,
preserving 39% of energy in glucose.

8. Cellular Respiration
Glycolysis: occurs in cytosol; degrades glucose into pyruvate
Kreb’s Cycle: occurs in the mitochondrial matrix; converts pyruvate into carbon dioxide
Electron Transport Chain: inner membrane of mitochondrion; electrons are passed to oxygen

9. Order of Events and how it leads into Aerobic Respiration.
* First we will look at Glycolysis
and how it leads into Aerobic Respiration.
* Second we will look at our other pathway of Glycolysis into Fermentation.

10. Glycolysis Glycolysis is the breakdown of glucose to two pyruvate.
Enough energy is released for immediate buildup of two ATP.
Two NADH are also produced.
Glycolysis takes place outside the mitochondria and does not utilize oxygen (anaerobic).

12. ATP Production in Glycolysis

13. Glycolysis
Glucose (C6) splits into two C3 molecules each with a phosphate group.
4 total ATP are produced but two are used to phosphorylate glucose so there is a net gain of 2 ATP.
The C3 molecules, pyruvate, enter the mitochondria if O2 is available to continue with aerobic respiration.
If no O2 is available, glycolysis becomes part of fermentation.
Let’s look at an aerobic environment first…

14. Inside The Mitochondria
Glucose breakdown involves the transition rxn, the Krebs cycle, and the electron transport system.
A mitochondrion has a double membrane with an intermembrane space between the outer and inner membrane.

15. Inside the Mitochondria

16. Inside the Mitochondria
Outer Membrane
Intermembrane space
Inner Membrane
Cristae
Folds of inner membrane.
Increases surface area for chemiosmosis
ETS occurs here
Matrix
Jelly-like substance
Transition Reaction and Kreb’s Cycle occur here.

17. The Mitochondria

18. Transition Reaction
The Transition Reaction links Glycolysis and the Krebs cycle.
Pyruvate is oxidized to an acetyl group attached to co-enzyme A and CO2 is removed.
This happens
twice for each
glucose molecule.

19. The Krebs Cycle
The Krebs cycle is a series of reactions that give off CO2 and producing ATP.
It occurs in the matrix of the mitochondria.
The Krebs cycle produces two immediate ATP molecules per glucose molecule.
6 NADH and 2 FADH2 are also formed and carry electrons to the ETS.
CO2 is released- we exhale it.

21. The Electron Transport System
Electron transport system is located in cristae of mitochondria.
Consists of carriers that pass electrons.
Electrons pass from higher to lower energy states, energy is released and stored for ATP production.
Electrons that enter the electron transport system are carried by NADH and FADH2
NADH gives up electrons, becoming NAD+
System accounts for 32 to 34 ATP depending on the cell.

22. The Electron Transport System
At each sequential oxidation-reduction rxn, energy is released to form ATP.
O2 serves as a terminal electron acceptor and combines with hydrogen to form water.
Because O2 must be present for system to work, it is called oxidative phosphorylation.

23. The Electron Transport System
At each sequential oxidation-reduction rxn, energy is released to form ATP.
O2 serves as a terminal electron acceptor and combines with hydrogen to form water.
Because O2 must be present for system to work, it is called oxidative phosphorylation.

24. Cristae of Mitochondria
NADH dehydrogenase complex, cytochrome b-c complex, and cytochrome oxidase complex all pump H+ ions into the intermembrane space.
Energy released from flow of electrons down electron transport chain is used to pump H+ ions, carried by NADH and FADH2, into intermembrane space.

25. ATP Production in the Mitochondria
ATP synthase complexes are channel proteins that also serve as enzymes for ATP synthesis.
As H+ ions flow from high to low concentration, ATP synthase synthesizes ATP (Chemiosmosis).
Once formed, ATP molecules diffuse out of the mitochondrial matrix through channel proteins.

26. Energy Yield From Glucose Breakdown
Source
FADH2
NADH
ATP
Glycolysis
2 ATP
2 NADH
4-6 ATP
Transition
6 ATP
Kreb’s
6 NADH
18 ATP
2 FADH2
4 ATP
TOTAL:
36-38 ATP

28. Anaerobic Pathway
If O2 is not available to the cell, fermentation, an anaerobic process, occurs.
During fermentation, glucose is incompletely metabolized to lactate or CO2 and alcohol.
Fermentation results in a net gain of only 2 ATP per glucose molecule.

29. Fermentation
Fermentation consists of glycolysis plus reduction of pyruvate to either lactate or alcohol and CO2.
NADH passes its electrons to pyruvate instead of to an electron transport system.
NAD+ is then free to return and pick up more electrons during earlier rxns of glycolysis.

30. Fermentation Examples
Anaerobic bacteria produce lactic acid when we manufacture some cheeses.
Anaerobic bacteria produce industrial chemicals: isopropanol, butyric acid, etc.
Yeasts use CO2 to make bread rise and produce ethyl alcohol in wine-making.
Animals produce pyruvate to lactate when it is produced faster than it can be oxidized by Krebs cycle.

31. Advantages and Disadvantages of Fermentation
Fermentation provides quick bursts of ATP energy for muscular activity.
Disadvantage is that lactate is toxic to cells.
When blood can’t remove lactate from muscles, lactate changes pH and causes muscles to fatigue.
Individual is in oxygen debt b/c oxygen is still needed after exercising.
Recovery occurs after lactate goes to liver.

32. Efficiency of Fermentation
Two ATP produced per glucose molecule during fermentation .
Fermentation is much less efficient than complete breakdown of glucose in oxidative phosphorylation..