1. Cellular Respiration

2. Nutrients + oxygen water+ ATP+ CO2
Cellular respiration – process in which mitochondria break down food molecules to produce ATP in plants & animals; occurs in the presence of oxygen
Nutrients + oxygen water+ ATP+ CO2
The equation for cellular respiration is:
6O2 + C6H12O6 → 6CO2 + 6H2O + Energy
oxygen + glucose → carbon dioxide + water + energy
Process changes organic chemical energy (glucose) into inorganic chemical energy ATP

3. Overview of Cellular Respiration
3 Stages:
Glycolysis – anaerobic process; does not require oxygen - cytoplasm
Citric Acid (Krebs) Cycle – aerobic; does require oxygen – mitochondria
Electron Transport Chain – aerobic; does require oxygen - mitochondria

4. Glycolysis
Glycolysis – breaks down glucose into two molecules of pyruvic acid (colorless acid)
This reaction uses enzymes and takes place in the cytoplasm of the cell (anaerobic reaction)
Produces:
2 Pyruvic acid molecules (used in Step 2 of cellular respiration)
2 ATP molecules (energy cell can use)
2 NADH molecules (electron carrier)

5. At the beginning of glycolysis, the cell uses up 2 molecules of ATP to start the reaction.
4 ADP
2 ATP
4 ATP
2 ADP
2 ATP
2NAD+
2 Pyruvic
acid 2
To the electron transport chain

6. Fermentation
Fermentation releases energy from food molecules by producing ATP in the absence of oxygen; anaerobic process
During fermentation, cells convert NADH to NAD+ by passing high- energy electrons back to pyruvic acid.
This action converts NADH back into NAD+, and allows glycolysis to continue producing a steady supply of ATP.

7. 2 Types of Fermentation
1. Lactic acid fermentation – process that supplies energy when O2 is scarce
Ex.) released during vigorous exercise; “feel the burn”
2. Alcoholic fermentation – used to produce CO2 and ethyl alcohol
Ex.) Yeast Cells

8. The Krebs Cycle
Named after Hans Krebs – British biochemist; won Nobel Prize in 1953 for discovery of this cycle
Aerobic process
Pyruvic acid produced from glycolysis along w/O2 start the 2nd stage of cellular respiration
Pyruvic acid is broken down into CO2 in a series of endergonic reactions

9. 2 Parts of the Krebs Cycle
Part A Step 1: Cycle begins when pyruvic acid enters the mitochondrion

10. The Krebs Cycle
2. Carbon molecule is removed, forming CO2, & electrons are removed, changing NAD+ to NADH.
3. Coenzyme A joins the 2-carbon molecule, forming acetyl-CoA.

11. The Krebs Cycle Citric acid
4. Acetyl-CoA then adds the 2-carbon acetyl group to a 4-carbon compound, forming citric acid.
Citric acid

12. The Krebs Cycle
Part B
Step 1: Citric acid is broken down into a 5-carbon compound, then into a 4-carbon compound.

13. The Krebs Cycle
Step 2: Two more molecules of CO2 are released and electrons join NAD+ and FAD, forming NADH and FADH2.

14. The Krebs Cycle
Result: 1 molecule of ATP is produced

15. Energy totals from 1 molecule of pyruvic acid is :
4 NADH
1 FADH2
1 ATP
Electron Transport Chain = 3rd step in cellular respiration, aerobic process, uses the high-energy electron carriers from the Krebs Cycle to convert ADP into ATP.
Carrier molecules produced are used to generate ATP via the Electron Transport Chain

16. Electron Transport Chain
High-energy electrons from NADH and FADH2 are passed along the electron transport chain from one carrier protein to the next.

17. The Totals
Glycolysis produces just 2 ATP molecules per molecule of glucose.
The complete breakdown of glucose through cellular respiration, including glycolysis, results in the production of 36 molecules of ATP.

18. The Totals: Overview

19. Comparing Photosynthesis and Cellular Respiration
The energy flows in photosynthesis and cellular respiration take place in opposite directions.

20. On a global level, photosynthesis and cellular respiration are also opposites.
Photosynthesis removes carbon dioxide from the atmosphere and cellular respiration puts it back.
Photosynthesis releases oxygen into the atmosphere and cellular respiration uses that oxygen to release energy from food.