1. The Process of Cellular Respiration
The gory details!!!!

2. Overview Respiration occurs in three metabolic stages: 1. Glycolysis
2. Krebs cycle (Citric acid cycle)
3. Electron transport chain and oxidative phosphorylation

3. 1. Glycolysis
Glucose (a six carbon-sugar), is broken down into two molecules of a compound called pyruvate.
Occurs in the cytosol
10 steps!! … each catalyzed by an enzyme
Can occur without oxygen
If O2 is present, pyruvate moves to the Krebs cycle
Payoffs: -2 ATP + 4 ATP = 2 ATP and
2 NADH

4. Energy Investment Phase

5. Energy Payoff Phase

6. 2. The Krebs Cycle If O2 present: pyruvate enters mitochondrion
Upon entering pyruvate is converted to a compound called acetyl coenzyme A (acetyl CoA)
CO2 is removed
1 NADH is made
x 2
enzymes of the Krebs cycle complete the oxidation of the organic fuel to carbon dioxide

7. Krebs Cycle Payoffs
This cycle begins when acetate from acetyl CoA combines with oxaloacetate to form citrate.
Ultimately, the oxaloacetate is recycled and the acetate is broken down to CO2.
Each cycle (8 steps!) produces:
1 ATP
3 NADH
1 FADH2 (another electron carrier)
per acetyl CoA so MULTIPLY BY 2 FOR TOTAL per glucose molecule

9. The conversion of pyruvate and the Krebs cycle produces large quantities of electron carriers.
Where do these electron carries go?

10. 3. Electron Transport Chain and Oxidative Phosphorylation
The vast majority of the ATP comes from the energy in the electrons carried by NADH and FADH2
The energy in these electrons is used in the electron transport system to power ATP synthesis.

11. Electron Transport Chain Details
Thousands of copies of the
electron transport chain are
found in the extensive surface of the cristae, the inner membrane of the mitochondrion.
Most components of the chain are proteins that can alternate between reduced and oxidized states as they accept and donate electrons.
Electrons drop in free energy as they pass down the electron transport chain.

12. Electrons carried by NADH are transferred to the first molecule in the electron transport chain, flavoprotein.
The electrons carried by FADH2 are added to the chain at a lower energy level.
Proteins called cytochromes pass electrons to O2, which picks up a pair of H+ ions to form 2 H2O

13. Does the Electron Transport Chain make ATP?!
The electron transport chain does NOT make any ATP directly.
It eases the fall of electrons from food to oxygen, releasing energy in manageable amounts.
The energy is used for chemiosmosis (and ATP synthesis) to occur
So who makes the ATP and what is the process called?

14. Oxidative Phosphorylation
ATP synthase: protein complex that makes ATP
It uses the energy of the proton gradient that develops between the intermembrane space and the matrix.
Process is called oxidative phosphorylation:
ATP synthesis powered by the flow of H+ across the membrane

15. The Big Picture!

16. Explanation of The Big Picture: Chemiosmosis
Chemiosmosis: an energy-coupling mechanism that uses energy stored in the form of an H+ gradient across a membrane to drive cellular work
In this case: coupling of the redox reactions of the electron transport chain to ATP synthesis
The electron transport chain pumps H+ across the membrane from the matrix into the intermembrane space
As the H+ diffuses back to the matrix they must pass through ATP synthase
This flow drives the oxidative
phosphorylation of ADP to ATP
Makes about 34 ATPs

17. Total: 38 ATPs!

18. Fermentation Occurs if oxygen is NOT present: anaerobic
Glycolysis generates 2 ATP whether oxygen
is present (aerobic) or not
But there must be a supply of NAD+ to accept electrons
Since NADH can not transfer electrons to oxygen in the electron transport chain, the electrons are transferred to pyruvate instead
Fermentation: glycolysis + reactions that regenerate NAD+ by transferring electrons from NADH to pyruvate
2 types…

19. Alcohol Fermentation
Pyruvate is converted to ethanol in two steps.
pyruvate is converted to a two-carbon compound, acetaldehyde by the removal of CO2.
acetaldehyde is reduced by NADH to ethanol
Alcohol fermentation by yeast is used in brewing and winemaking
Also used by some bacteria

20. Lactic Acid Fermentation
pyruvate is reduced to form lactate (ionized form of lactic acid) - No release of CO2
Used some fungi and bacteria is used to make cheese and yogurt.
Muscle cells use this when to generate ATP when O2 is scarce.
The waste product may cause muscle fatigue, but ultimately it is converted back to pyruvate in the liver.

21. Fermentation and cellular respiration are anaerobic and aerobic alternatives, respectively, for producing ATP from sugars.
Both use glycolysis to oxidize sugars to pyruvate with a net production of 2 ATP by substrate-level phosphorylation.
Both use NAD+ as an electron acceptor.
In fermentation, the electrons of NADH are passed to an organic molecule, regenerating NAD+.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

22. In respiration, the electrons of NADH are ultimately passed to O2, generating ATP by oxidative phosphorylation.
In addition, even more ATP is generated from the oxidation of pyruvate in the Krebs cycle.
Without oxygen, the energy still stored in pyruvate is unavailable to the cell.
Under aerobic respiration, a molecule of glucose yields 38 ATP, but the same molecule of glucose yields only 2 ATP under anaerobic respiration.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

23. Review:
For each of the following steps of cellular respiration, explain the reactants, products, location, and purpose:
Glycolysis
Krebs cycle (citric acid cycle)
Oxidative phosphorylation and chemosynthesis (Electron transport chain)
When does fermentation occur? Give a real example of this.
Compare the different types of fermentation.
Summarize all of cellular respiration in one paragraph.