1. Chapter 9
Cellular Respiration

2. Cellular Respiration
Release of potential energy in organic molecules (food) to produce ATP – which is the form of energy used in the cell.
Potential energy is primarily in C-H bonds. When molecules containing these are oxidized, the H and accompanying electrons are released and energy is released.
With the input of heat (activation) energy,
CH4 + 2O CO2 + 2H20 + heat
Compare this to what happens to glucose
C6H12O6 + 6O CO2 + 6H2O + heat (-686 kcal/m)
free energy change
In living things, the temp is not adequate to overcome the required activation energy to ignite glucose so enzymes lower the energy of activation.

3. Releasing energy from carbohydrates
Oxidation of glucose
Electrons from C-H bonds in glucose can be transferred to a lower energy state and the energy in the bonds converted to ATP bonds or heat.
Stepwise oxidation releases the energy in small packets that are manageable rather than in one big bang.

4. Some energy directly phosphorylates ADP and some of the energy is transferred with electrons to NAD+ to release to an ATP generating pathway.
Substrate level phosphorylation
Enzyme takes a phosphate from a substrate & attaches to ADP ATP
Chemiosmotic phosphorylation (from ETC)
H + ion concentration gradient across membrane
H + flow from high to low through ATP synthase
ADP + P ATP

5. Important Molecules NAD+ - oxidizing agent - Coenzyme FAD - Coenzyme
It causes electrons to leave an organic molecule.
It transports those electrons to an ATP generating area where it releases them.
FAD - Coenzyme
Transports electrons
Electron Transport Chain Molecules
Molecules built into membranes that receive & release electrons stepwise to lower their energy level to the point where they (electrons) are accepted by O2 (final electron acceptor).
In some of these steps, ATP is produced.

6. Glycolysis – in cytoplasm of almost all cells
Glucose 1
Glucose 6-phosphate 2
Fructose 6-phosphate 3
Fructose 1, 6 Diphosphate 4
2 Glyceraldehyde Phosphate (PGAL ) 5
2 Diphosphoglycerate (DiPGA) 6
2 Phosphoglycerate (PGA) 7
2 Phosphoenolpyruvate (PEP) 8
2 Pyruvate
Steps 1-3 add energy to glucose so it will be more reactive – USES 2 ATP
Step 5 is oxidation w/ electrons transferred to NAD – also phosphorylation
Step 6 – ATP produced by pulling P off DiPGA
Step 7 – Water removed
Step 8 – ATP produced
Forms – 4 ATP, 2 NADH
Nets – 2 ATP, 2 NADH

7. Oxidation of Pyruvate Happens in the Mitochondria
Everything from this point on happens TWICE for 2 pyruvate from 1 Glucose molecule
NAD+ NADH
CoA + Pyruvate Acetyl –CoA
CO2 (decarboxylation)
CoA is a coenzyme made from the vitamin pantothenic acid
Produces 2 NADH, 2 CO2
Junction between glycolysis & Krebs Cycle

8. Krebs Cycle – Acetyl CoA goes in
Citrate(6 C) Oxaloacetate 5 C Acid 4 C Acid 4 C Acid 4 C Acid
NAD+
NADH
NADH
NAD+
NAD+
CO2
NADH
H2O
ADP + P
FADH2
ATP
FAD

9. Krebs Cycle Totals Total for 2 Acetyl = 6 NADH shuttles electrons
2 FADH2 to ETC
2 ATP
4 CO2

10. Purposes of steps 1-3 Glycolysis Oxidation of Pyruvate
Krebs Cycle (Citric Acid Cycle)

11. Electron Transport Chain & Chemiosmosis
The molecules of ETC are in the cristae (inner membrane)
Electrons released from NADH or FADH2 flow through the cytochromes, to lower & lower energy levels until they are accepted by O2 (the final electron acceptor that produces H2O)
As they flow, protons are pumped out of the matrix into the innermembrane space.

12. ETC, cont.
As protons build up to higher concentration, they flow back into the matrix through an enzyme, ATP Synthase, and ATP is made - Chemiosmosis
Can also be called oxidative phosphorylation
Controlled release of energy for ATP synthesis
H+ flows back in once gradient occurs through ATP Synthase to produce ATP
ATP Synthase acts as a molecular mill that produces ATP from ADP and P

13. ETC Diagram

14. Purpose of ETC
ETC

15. Grand Total of ATP

16. Anaerobic Catabolism of organic molecules
Fermentation
Only generates ATP by substrate level phosphorylation
As long as there is a sufficient supply of NAD+
Without NAD+, glycolysis would shut down for lack of oxidizing agent
Two types
Alcohol fermentation
Step 1 - Release CO2 from pyruvate & convert to acetaldehyde
Step 2 - Acetaldehyde reduced by NADH to ethanol – regenerates NAD+ to continue glycolysis
Happens in Yeast and Bacteria

17. Fermentation, cont. Lactic Acid Fermentation
Pyruvate reduced directly by NADH to form lactate with no release of CO2
Human muscle cells make ATP by LAF when O2 is scarce.
During early strenuous exercise
When sugar catabolism for ATP outpaces muscle’s supply of O2 from blood - Cells switch to fermentation
Lactate accumulation – causes fatigue and pain*
Lactic acid is carried back to liver and converted back to Pyruvate
*New studies believe it is Potassium that causes the muscle pain and fatigue and that lactate actually enhances muscle performance.

18. Glucose Pyruvate Ethanol Acetyl CoA or Lactate Kreb’s
Path of Pyruvate
Glucose Pyruvate Ethanol Acetyl CoA or Lactate Kreb’s
No O2 present - fermentation
O2 present – cellular respiration