1. Notes: Cellular Processes (Part 3) Cell Respiration
CELL ENERGY, PHOTOSYNTHESIS, AND CELLULAR RESPIRATION

2. Part 3 Cellular Respiration
Plants are the main producers of glucose via photosynthesis. Both plants and animals break glucose down to release its stored energy for different cell processes.

3. 1. Overview of Cellular Respiration
Like a bank storing money, glucose stores energy. Each bond in the glucose molecule can be broken down to release energy for necessary cell processes. The equation is basically the reverse of the photosynthesis equation.
oxygen + glucose carbon dioxide + water + energy
6O C6H12O → CO H2O + Energy (ATP)

4. 1. Overview of Cellular Respiration
Cellular Respiration has three main processes: glycolysis, the Krebs Cycle, and the Electron Transport Chain. Glycolysis is anaerobic, meaning oxygen is not needed. The Krebs Cycle and the ETC are both aerobic, meaning oxygen is required.

5. 2. Glycolysis
The prefix “glycol” means sweet, and the suffix “lysis” means to cut or break. Glycolysis is the first initial cut of the sugar molecule glucose.

6. 2. Glycolysis
A. First, two ATPs cut 6-carbon glucose into two 3-carbon molecules called G3P. Second, the 3-carbon molecules are rearranged into a different 3-carbon molecule called pyruvate. When pyruvate is formed, 4 ATP and 2 NADH molecules are made. (Recall NADP+ and NADPH are similar molecules used in photosynthesis.)

7. 2. Glycolysis
B. The summation of glycolysis: Input of 1 glucose and 2 ATP. Output of two 3-carbon pyruvates, 4 ATP and 2 NADH. The net (overall) total of ATPs made is 2. Most energy is still stored in the pyruvate molecules.

8. 3. Krebs Cycle
The goal is to release the remaining energy stored in pyruvate molecules while releasing carbon dioxide waste. This is called the Krebs Cycle or citric acid cycle or tricarboxylic acid cycle.
A. The pyruvate molecules move into the mitochondrial matrix. A series of carbon molecule changes follow:

9. 3. Krebs Cycle
1. The 3-carbon pyruvate releases one carbon to CO2. The remaining 2-carbon molecule bonds with a four-carbon molecule that was recycled from the previous Krebs cycle. This required help from the enzyme Acetyl CoA.
2. The molecule is now a 6- carbon molecule. It will release a molecule of CO2 and again be a 5-carbon molecule.

10. 3. Krebs Cycle
3. Several energy carriers come to pick up energy, releasing another molecule of CO2 until all that remains is a 4-carbon molecule that is recycled back up to step 1 of the Krebs Cycle.

11. Krebs Cycle
A. The Krebs Cycle happens twice, since there were two pyruvate molecules from glycolysis.
B. The summary: the two pyruvate molecules provided a net total of 6CO2 molecules, 2 ATP molecules, 8 NADH molecules, and 1 FADH2 molecule.

12. 4. Electron Transport
A. When oxygen is available, aerobic respiration takes place. This is ideal, because the maximum amount of ATP is made in aerobic respiration. Electrons are transported through the matrix membranes of mitochondria, which has many proteins.

13. 4. Electron Transport
B. NADH releases its electron, again forming NAD+ and returning to the Krebs cycle.
C. FADH2 releases its electron, again forming FAD, which returns to the Krebs Cycle, and H+ ions.

14. 4. Electron Transport
D. The H+ ions are pumped through the matrix membrane, creating 32 net total ATP.
E. Oxygen also diffuses through the membrane, bonding with H+ ions to make H2O.

15. 4. Electron Transport
F. In eukaryotes, 36 total ATP molecules are made from each molecule of glucose. 2 ATP from glycolysis + 2 ATP from Krebs Cycle + 32 ATP from aerobic respiration = 36 ATP cellular respiration
G. Prokaryotes need energy, too, but do not have mitochondria. Instead of using the mitochondrial matrix, the cell membrane is used. Bacteria is so small, that the molecules don’t have to move around as much, saving energy. Prokaryotes get 38 ATP from each glucose molecule.

17. 5. Anaerobic Respiration
Oxygen isn’t always readily available. Either the environment the organism lives in doesn’t have a ready supply, or glucose is being broken down faster than oxygen supplies can be replenished. Glycolysis can occur, but will stop once NAD+ is used up. Some energy is better than none, so anaerobic respiration occurs, also called fermentation.

18. 5. Anaerobic Respiration A. Lactic Acid Fermentation
1. When cells cannot provide enough oxygen, like during rigorous exercise, muscle cells will make lactic acid. The lactic acid is painful in muscles when it builds up.
2. The two pyruvates from glycolysis are converted into lactic acid, which produces a molecule of NAD+, thus allowing glycolysis to continue.

19. 5. Anaerobic Respiration A. Lactic Acid Fermentation
3. Lactic acid fermentation does not allow much energy to be produced, and is not ideal.
4. Many microorganisms survive by lactic acid fermentation, which we use to make foods, like cheese, yogurt, and sour cream.

20. 5. Anaerobic Respiration B. Alcohol Fermentation
1. Many organisms like yeast or some bacteria survive due to alcohol fermentation Again after glycolysis, 2 pyruvates are formed. 2 CO2 molecules are released (think of the holes you see in slices of bread – made from the release of CO2!) and ethanol is produced The production of ethanol requires a NADH molecule to again become NAD+, returning to glycolysis.

21. 6. Photosynthesis and cellular Respiration: the Comparison!!
A. The Equations!
Photosynthesis
carbon dioxide + water light energy oxygen + glucose CO H2O → O C6H12O Cellular Respiration
oxygen + glucose carbon dioxide + water + energy
6O C6H12O → CO H2O + Energy (ATP)

22. 6. Photosynthesis and cellular Respiration: the Comparison!!
B. Energy:
Photosynthesis harvests energy from the sun, makes ATP and NADPH in the Light Reactions, then stores that energy in glucose molecules.
Cellular Respiration breaks down glucose molecules to release the stored energy when ATP is needed.

23. 6. Photosynthesis and cellular Respiration: the Comparison!!
C. Energy Carriers:
Photosynthesis Cellular Respiration ADP + P → ATP ADP + P → ATP
NADP+ → NADPH NAD+ → NADH
FAD → FADH2

24. 6. Photosynthesis and cellular Respiration: the Comparison!!
D. Which uses what?
Photosynthesis: Only plants and some bacteria
Chemosynthesis: only organisms near thermal vents deep under the ocean.
Cellular Respiration: Both plants and animals. Bacteria have a slightly different process because no mitochondria.

25. 6. Photosynthesis and cellular Respiration: the Comparison!!
E. The processes:
Intake
Photosynthesis
Output
Light reactions
light & H2O
Photosystem 2
O2, H+, e-
e-, NADP
Photosystem 1
NADPH
ADP + P
Chemiosmosis
ATP
Dark Reactions
CO2, ATP, NADPH
Calvin Cycle
Glucose
Intake
Cellular Respiration
Output
ADP, NAD+
Glycolysis
ATP, NADH, Pyruvates
Pyruvates, FAD, NAD+, ADP
Kreb’s Cycle
CO2, FADH2, ATP, NADH
O2, H+ (from FADH2, NADH)
Aerobic Resp.
H2O, ATP, FAD, NAD+

26. 6. Photosynthesis and cellular Respiration: the Comparison!!
F. The Locations:
Photosynthesis – light reactions in chloroplasts on thylakoid membranes, dark reactions in chloroplasts in stroma.
Cellular Respiration – glycolysis in cell cytoplasm, Krebs and aerobic respiration in mitochondrial matrix.