1. Cellular Respiration
How organisms convert food into usable energy

2. The Overall Process Organic molecule + Oxygen →
Carbon dioxide + Water + Energy
C6H12O6 + 6O2 → 6CO2 + 6H20 + Energy (ATP and heat)
Glucose is a very high energy molecule, carbon dioxide and water are not.
+ O2

3. Cellular Respiration
Cellular respiration occurs in ALL eukaryotes (Plants, animals, fungi, protists) and some bacteria
Glycolysis (the first step) occurs in ALL organisms

4. ATP Energy from food is not used directly
Energy is transferred in the form of ATP
Food is broken down and the energy released forms ATP, storing energy in the bonds between phosphate groups

5. ATP is Recycled
ATP is formed by combining ADP and Pi. Energy is released when ATP is split.

6. Glucose is Oxidized During Cellular Respiration
Glucose loses electrons to Oxygen, which can then bind with H ions and form water
Molecules with lots of C-H bonds are good sources of fuel, as they have lots of energy and electrons
i.e. fat

7. Remember Activation Energy, Ea?
Glucose releases a lot of energy when it is combusted
However, this doesn’t happen spontaneously due to Ea
Enzymes lower this energy of activation and allow the reaction to occur in many steps

8. Electrons Do Not Pass Directly to O2
Electrons are stripped from glucose one by one
They are passed to NAD+ to form NADH

9. NADH delivers electrons to the ETC
Electrons travel down the Electron Transport Chain
Each step of the ETC is more electronegative (wants the electrons more!)
Small amounts of energy are released in each step
Electrons eventually reach Oxygen (remember Oxygen is one of the most electronegative elements!)

10. Why So Many Steps? Glucose contains a lot of energy!
If all of the energy is released at once, you would get an explosion
Lots of energy is lost as light and heat

11. Cellular Respiration

12. 3 Parts of Cellular Respiration
Glycolysis
Glucose is oxidized into Pyruvate
Some ATP is made, along with some NADH
Krebs Cycle
Decomposes Pyruvate to Carbon Dioxide, making some ATP
Produces NADH and FADH2
ETC/Oxidative Phosphorylation
Produces lots of ATP from NADH and FADH2

13. Glycolysis Literally means “sugar splitting” Takes place in cytosol
Does not require mitochondria

14. Net Effects of Glycolysis
Glucose → 2 Pyruvate + 2 ATP + 2NADH

15. ATP Synthesized via Substrate-level Phosphorylation
Phosphate group is transferred from the sugar to ADP by an enzyme, forming ATP

16. Pyruvate → Acetyl CoA
Before entering the Krebs cycle, Pyruvate releases a Carbon Dioxide molecule
The remaining 2 carbons are oxidized to form acetate, producing NADH
They then combine with a molecule called Coenzyme A to form Acetyl CoA

17. The Krebs Cycle
Acetyl CoA enters the Krebs Cycle (aka Citric Acid cycle)

18. For every glucose... 2 Acetyl CoAs enter the Krebs cycle
4 CO2 molecules are released
6 NAD+ molecules are reduced to NADH
2 FADH2 molecules are formed from FADH+
2 ATP molecules are formed from ADP and Pi via Substrate-Level phosphorylation

19. Krebs Cycle

20. In even more detail...

21. Glycolysis + Krebs
From 1 Molecule of Glucose we have created: 2ATP + 2NADH (glycolysis) + 2NADH (Pyruvate → Acetyl CoA) + 6NADH + 2 FADH2 + 2ATP (Krebs cycle) = 10NADH + 4ATP + 2FADH2

22. Most ATP is Produced via the Electron Transport Chain
A series of proteins, each is more electronegative than the protein before it
So electrons give off a little energy each time as they are passed down the chain
Electrons eventually end up at O2

23. The Mitochondrial ETC
Found in the inner membrane (cristae)

24. NADH and FADH2 Hand off Electrons to the ETC
NADH and FADH2 drop off their electrons at different points in the ETC
NADH drops off electrons to FMN at the top of the chain
FADH2 drops off electrons a little ways into the chain
FADH2 will produce less ATP

25. Chemiosmosis
Each time an electron moves, an H+ ion is pumped across the membrane
This creates an electrochemical gradient as there is a much greater concentration of H+ ions in the intermembrane space
The only way H+ ions can diffuse into the matrix is through ATP synthase

26. Pumping Protons

27. ATP Synthase

28. Mechanism of ATP Synthase
Diffusing protons turn a cylinder (like water pushing a mill)
This causes the cylinder to essentially spin – changing the shape of the enzymatic regions of the protein
This activates the enzyme, synthesizing ATP

29. ATP Synthase produces ATP as H+ ions diffuse through it

31. Oxygen reduced to Water
Electrons at the end of the chain are donated to oxygen.
Oxygen, with these new electrons, can combine with H+ ions to form water.
4H+ + 4e- + O2 → 2H2O

32. For each molecule of Glucose...
34 ATPs are synthesized via oxidative phosphorylation
Each NADH produces 3 ATP
10NADH*3ATP = 30 ATP
Each FADH2 produces 2 ATP
2FADH2*2ATP = 4 ATP
Total = 34 ATP (roughly)
(plus 6 molecules of Water)

33. Review of Respiration

34. Chemical Summary
C6H12O6 + 6O2 + 38ADP + 38Pi
→ 6CO2 + 6H ATP

35. Efficiency of Cellular Respiration
40% of the energy is converted to ATP
Although it may sound low, this is a remarkably high amount
Cars at the most convert about 25% of their fuel to usable energy
The rest of the energy is lost as heat per the 2nd Law of Thermodynamics (entropy!)

36. Cellular Respiration Occurs in all eukaryotes and some bacteria
Glycolysis occurs in cytosol of ALL cells
The rest of respiration occurs in mitochondria
Krebs cycle in the mitochondrial matrix
ETC is in the inner membrane

37. Review Glyolysis – Sugar split, forming ATP and NADH
Krebs cycle – sugar fully broken down to CO2 forming NADH and FADH2
Oxidative phosphorylation – lots of ATP made via chemiosmosis

38. Aerobic Respiration The process we have learned is aerobic respiration
Oxygen is necessary
Glycolysis → Krebs Cycle → Oxidative Phosphorylation
Lots of ATP produced

39. Anaerobic Respiration
ATP can be made without oxygen (just not as much)
Glycolysis makes 2 ATP
NAD+ can oxidize glucose to pyruvate, generating ATP
But we must regenerate NAD+ as it is converted to NADH in glycolysis
This is solved by fermentation

40. Alcohol Fermentation
In alcohol fermentation pyruvate is converted to ethanol, regenerating NAD+
Yeast are used to make alcoholic beverages
Generates CO2

41. Lactic Acid Formation
Muscle cells can generate some ATP without oxygen
Glycolysis occurs
Fermentation converts pyruvate to lactate, regenerating NAD+

42. Lactic Acid Build-Up
When muscle cells cannot get oxygen fast enough (i.e. when you're sprinting) Lactic Acid Fermentation occurs
Build up of lactic acid is what makes muscles feel heavy and tired
Lactic acid is carried to liver where pyruvate can be regenerated
Lactic acid is also important in the making of cheese and yogurt

43. Glycolysis Evolved Early
Glycolysis evolved long before oxygen was present in the atmosphere
All cells undergo glycolysis
Aerobic respiration provides much more ATP, but some organisms can survive only by fermentation
Some organisms (and cells) can switch switch between fermentation and aerobic respiration
i.e. muscle cells
If oxygen is present, pyruvate enters Krebs cycle, if not it heads to fermentation

44. Other Sources of Fuel
Starch and glycogen can be broken down to glucose
Proteins can be converted to intermediates of respiration
Fatty Acids can be broken down to 2- carbon fragments that enter the Krebs cycle via Beta Oxidation
Provides lots of ATP

46. Feedback Inhibition
When excess ATP is present, it shuts off glycolysis, preventing accumulation of ATP and preserving energy stores