1. How Cells Release Stored Energy – Cellular Respiration

2. Aerobic Respiration: Whole Organism
Aerobic respiration at the whole organism level = process by which gases are exchanged with the environment. O2
CO2

3. Aerobic Respiration: Whole Organism
Respiratory Surface (= part of the organism where O2 diffuses into and CO2 diffuses out of the organism) must be moist, as gases must be dissolved in water before they can diffuse in or out.

4. Aerobic Respiration: Whole Organism
In unicellular aquatic protozoans: O2 dissolved in water passes across the cell membrane by diffusion, and CO2 exits.
CO2 O2

5. Aerobic Respiration: Whole Organism
Planarian
In multicellular aquatic plants and invertebrate animals: O2 dissolved in water enters cells by diffusion, and CO2 exits by diffusion. O2
CO2
Elodea cell

6. Aerobic Respiration: Whole Organism
In insects: O2 enters through small openings in the body wall (spiracles) and is carried through tracheal tubes to moist cell membranes, across which respiratory exchange occurs.
Spiracles
SEM
spiracle

7. Aerobic Respiration: Whole Organism
In fish: O2 (in H2O) diffuses across the surface of gills, into capillaries of the circulatory system and CO2 diffuses in the opposite direction.

8. Cellular Respiration: THE BIG PICTURE
Cellular respiration is the process by which organisms can get energy (ATP) from their food (glucose)
Cellular respiration is CRITICAL for life
Occurs in BOTH plants and animals
Two main mechanisms
Aerobic cellular Respiration – Requires Oxygen
Anaerobic cellular Respiration – Does not require Oxygen

9. Main Types of Cellular Respiration Pathways
Aerobic Respiration
Evolved later
Require oxygen
Start with glycolysis in cytoplasm
Completed in mitochondria
Anaerobic Respiration
Evolved first
Don’t require oxygen
Start with glycolysis in cytoplasm
Completed in cytoplasm

10. Aerobic Respiration Overall Equation: C6H1206 + 6O2 6CO2 + 6H20
glucose oxygen carbon water
dioxide
Several steps occur in the middle (intermediates)
Each step (rxn) catalyzed by enzymes

11. Aerobic respiration Overview
Stage One:
Glycolysis (cytoplasm)
Stage Two:
Preparation for Krebs (mitochondrial matrix)
Krebs Cycle (matrix)
Stage Three:
Electron Transfer Chain (across inner membrane of mitochondria)

13. The Role of Carrier Molecules
Several oxidation-reduction rxns take place in aerobic respiration (Glucose gets oxidized to carbon dioxide)
In order to aid in the redox rxns, enzymes use carrier molecules NAD+ and FAD to carry electrons from broken down glucose to the electron transfer chain
NAD+ and FAD accept electrons and hydrogen to become NADH and FADH2 during the first two stages of aerobic respiration (Glycolysis, Krebs) and deliver electrons and hydrogen to the Electron Transfer Chain to make ATP

14. Stage One: Glycolysis
Glucose (6-carbon) is broken down into 2 molecules of pyruvate (3-carbon)
Yields 2 ATP by substrate level phosphorylation

15. Glycolysis: Overall Reaction
2 ADP
2 ATP
G3P
(3C)
Pyruvate
(3C)
2 NAD+
2 NADH
2 ATP
2 ADP
Glucose
(6C)
Fructose
Bisphosphate
(6C)
2 NAD+
2 NADH
G3P
(3C)
Pyruvate
(3C)
2 ADP
2 ATP

16. Aerobic Respiration: 1. Glycolysis

17. Glycolysis: Net Yield Energy requiring steps: 2 ATP invested
Energy releasing steps:
2 NADH formed
4 ATP formed
Net yield:
2 ATP + 2 NADH + 2 molecules of Pyruvic Acid

18. What happens next? Depends on the organism and the presence of oxygen
If oxygen is around: Aerobic respiration, proceed to Krebs cycle
If no oxygen: Anaerobic respiration, Proceed to Fermentation

19. Second Stage: Krebs cycle
Preparatory reactions: Oxidation of pyruvate
Pyruvic acid is oxidized into two-carbon acetyl CoA units and carbon dioxide
NAD+ is reduced into NADH2
Krebs cycle
The acetyl units are oxidized to carbon dioxide
NAD+ and FAD are reduced into FADH and NAHD2

20. Oxidation of Pyruvate

22. The Krebs Cycle Overall Reactants Overall Products Acetyl-CoA 3 NAD+
FAD
ADP and Pi
Overall Products
Coenzyme A
2 CO2
3 NADH
FADH2
ATP

23. Results of the Second Stage
All of the carbon atoms in pyruvate end up in carbon dioxide
NAD and FAD are reduced (they pick up electrons and hydrogen)
One molecule of ATP forms
Four-carbon oxaloacetate regenerates

24. NAD/FAD Reductions during First Two Stages
Glycolysis 2 NADH2
Preparatory
reactions NADH2
Krebs cycle FADH NADH2
Total FADH NADH2

25. Electron Transfer Chain
Occurs in the mitochondria
Coenzymes deliver electrons to electron transfer chains
Electron transfer sets up H+ ion gradients
Flow of H+ down gradients powers ATP formation

28. Importance of Oxygen Oxygen is the finial Electron acceptor
Electron transport chain requires the presence of oxygen
Oxygen withdraws spent electrons from the electron transfer chain, then combines with H+ to form water

29. Summary of Energy Harvest (per molecule of glucose)
Glycolysis
2 ATP formed by
Krebs cycle and preparatory reactions
2 ATP formed
Electron transport chain
32 ATP formed

31. Efficiency of Aerobic Respiration
686 kcal of energy are released
7.5 kcal are conserved in each ATP
When 36 ATP form, 270 kcal (36 X 7.5) are captured in ATP
Efficiency is 270 / 686 X 100 = 39 percent
Most energy is lost as HEAT!

32. Anaerobic Pathways Do not use oxygen
Produce less ATP than aerobic pathways

33. Fermentation Pathways
Begin with glycolysis
Do not break glucose down completely to carbon dioxide and water
Yield only the 2 ATP from glycolysis
Steps that follow glycolysis serve only to regenerate NAD+

36. Evolution of Metabolic Pathways
When life originated, atmosphere had little oxygen
Earliest organisms used anaerobic pathways
Later, noncyclic pathway of photosynthesis increased atmospheric oxygen
Cells arose that used oxygen as final acceptor in electron transport

37. Summary of Cellular Respiration
Process
Where Process Occurs
Net Gain of ATP
Per Glucose
Anaerobic Glycolysis & Fermentation
Cytoplasm
2 ATP
Aerobic Krebs Cycle and Electron Transport
Mitochondrion
36 ATP

38. ATP / ADP Cycle ATP is constantly being used and remade in the cell.
Energy is released or stored by breaking or making a phosphate bond.