1. Chapter 9 – Cellular Respiration: Harvesting Chemical Energy

2. Energy Flow Energy flow in an ecosystem
Enters as sunlight, leaves as heat
Produces ATP
Involves photosynthesis and cellular respiration

3. REDOX Reactions Transfer of 1 or more electrons
Oxidation – partial or complete loss of electrons
Reduction – partial or complete gain of electrons
OIL RIG – oxidation is losing, reduction is gaining
Oxidizing agent is the electron acceptor
Reducing agent is the electron donor
Simple non-biological example
Na + Cl  Na+ + Cl-
Na becomes oxidized (loses electron) while Cl becomes reduced (gains electron)
Na is the reducing agent, Cl is the oxidizing agent

4. REDOX cont. Cellular Respiration
C6H12O6 + 6O2  6CO2 + 6H2O + energy (ATP)
C6H12O6 becomes oxidized to CO2
O2 becomes reduced to H2O
Once activation energy barrier breeched, release 686 kcal or 2870 kJ per mole of glucose
Use this energy to make ATP (yields 7.3 kcal or 30.5 kJ/mole)
Enzymes help to breech the activation energy

5. Electron Transfer
If the energy from glucose is released all at once, it cannot be harnessed efficiently
Use the coenzyme NAD+ (nicotinamide adenine dinucleotide)

6. Electron Transport Chains
How do electrons that are extracted from glucose and stored as NADH finally reach oxygen?
Use electron transport chains to break the fall of electrons into several energy releasing steps

7. Stages of Cellular Respiration
1. Glycolysis – breaks glucose into 2 pyruvates
2. The Citric Acid Cycle – completes the breakdown of glucose by oxidizing pyruvate into carbon dioxide
3. Oxidative phosphorylation: electron transport and chemiosmosis – produces ATP

8. Stages of Cellular Respiration

9. Glycolysis “sugar splitting”
Energy investment phase – 2 ATP, split glucose into 2, 3C intermediates
Energy payoff phase – form 4 ATP, 2 NADH, 2 waters, and 2, 3C pyruvate molecules

11. Glycolysis
Animation
..\ppt lectures cd\animations\09_09Glycolysis_A.swf
The net gain of 2 ATP made by substrate phosphorylation

12. Oxidation of Pyruvate (pre-TCA)
Completes the oxidation of glucose, currently in the form of pyruvate
Pyruvate from cytosol moves into the mitochondria via a transport protein
The carboxyl group (already oxidized) is removed and given off as CO2
Remaining 2 carbon molecule oxidized into acetate while the electrons are transferred to NAD+
Coenzyme A is attached to acetate to make acetyl CoA

13. The Citric Acid Cycle
Acetyl CoA enters the Citric Acid Cycle by combining with oxaloacetate to form citrate
Exergonic cycle; energy used to reduce NAD+ and FAD+
For every turn of the cycle:
2 carbon atoms enter while 2 different carbons leave as CO2
Coenzymes are reduced; 3 NADH and 1FADH2
1 ATP produced through substrate-level phosphorylation
Oxaloacetate is regenerated
2 turns of the cycle required to completely oxidize 1 glucose

14. TCA Cycle Acetyl CoA enters making citrate Converted to isocitrate
Lose CO2, reduce NAD+ to NADH
Lose CO2, reduce NAD+, attached to CoA
Add P, remove P, attach to GDP  GTP  ADP  ATP
Remove 2 H, form FADH2
Add H2O, rearrange
Reduce NAD+, reform oxaloacetate

15. The Citric Acid Cycle Animation
..\ppt lectures cd\animations\09_12CitricAcidCycle_A.swf

16. Electron Transport Chain
Made of proteins embedded in the inner mitochodrial membrane, mostly cytochrome proteins
The electrons fall from NADH to Oxygen yielding 53 kcal/mol, but not all at one time
Energy released is coupled to chemiosmosis
Animation
Animation2

17. Electron Transport

18. ATP Synthase Makes ATP from ADP and inorganic phosphate
Works like a reverse ion pump
H+ ions move through the protein causing the addition of phosphate to ADP
Animation
Experiment animation

19. Chemiosmosis
NADH and FADH2 shuttle high energy electrons to the electron transport chain
Energy from these electrons shuttles H+ ions from matrix to intermembrane space
Creates a concentration gradient, H+ ions move through ATP synthase via facilitated diffusion back to the matrix
Creates ATP from ADP and inorganic phosphate

20. ATP Production Overview

21. ATP Totals Why 36 to 38 ATP? Why not an exact number?
The phosphorylation and redox reactions are not directly coupled. 1 NADH results in 10 H+, takes 3 to 4 H+ to make ATP, so yield is between 2.5 and 3.3 ATP. 1 FADH2 yields between 1.5 and 2 ATP.
Electrons in NADH outside of mitochondria must be passed into the mitochondria through an electron shuttle (NADH impermeable to membrane) and transferred to either NAD+ (liver, heart) or FAD+ (brain).
Some of the proton motive force is used to pull in pyruvate from cytosol.
Approximatelyl 40% of the energy in glucose is transferred to ATP, the rest is lost as heat.

22. Fermentation In the absence of oxygen (anerobic)
Alcohol Fermentation – in many bacteria and yeast
Lactic Acid Fermentation – in human muscles
Net yield 2 ATP, from glycolysis

23. Question
The oxidation of glucose to carbon dioxide releases kcal/mole of energy. If all of this energy is released at one time, then most of it would be lost as heat. Burning the energy all at once would be akin to igniting your gas tank in order to run your car, rather than burning small amounts of gasoline slowly in the engine. If the energy of glucose is released slowly, in several small steps, then the potential energy available could be captured at each step rather than a single explosive release.
In groups of 3 answer the following questions:
How are the steps in the cell respiration process consistent with the concepts of stepwise release of energy to capture the maximum amount of potential energy?
Explain how it is better for a cell to use many reactions to oxidize glucose even though each reaction needs a specific enzyme (which is costly to the cell to produce).