1. Cellular Respiration
Chapter 9

2. Chemical Pathways Food serves as the source of energy for cells.
Stores a lot of energy
1 gram of glucose releases 3811 calories of heat energy when burned in the presence of oxygen
calorie: amount of energy needed to raise 1 gram of water 1 degree Celsius

3. Chemical Pathways
Cells don’t burn glucose or other food compounds – they gradually release energy
Cellular respiration: the process that releases energy by breaking down glucose and other food molecules in the presence of oxygen
Equation: (you must memorize)
6O2 + C6H12O6  6CO2 + 6H2O + energy

4. Chemical Pathways There are three main stages of cellular respiration:
1st – Glycolysis
2nd – Krebs Cycle
3rd – Electron Transport Chain (ETC)
When there is no oxygen present, glycolysis is followed by fermentation.

5. Cellular Respiration

6. Glycolysis
The process in which one molecule of glucose is broken in half, producing 2 molecules of pyruvic acid (a 3-Carbon compound)
Takes place within the cytoplasm
ATP
In glycolysis, the cell has to put in 2 ATP
The cell then releases 4 ATP at the end of glycolysis
This results in a net gain of 2 ATP
Also produces 2 NADH by adding a pair of high-energy electrons to NAD+

7. Glycolysis

8. Fermentation Occurs after glycolysis in the absence of oxygen
Fermentation releases energy from food molecules by producing ATP
Anaerobic – absence of oxygen is required
Cells convert NADH back into the electron carrier NAD+, which is needed for glycolysis
This allows glycolysis to continue producing a steady supply of ATP

9. Fermentation 2 types of fermentation Alcoholic Fermentation
Yeasts and some other microorganisms
Pyruvic acid + NADH  alcohol + CO2 + NAD+
Lactic Acid Fermentation
Occurs in muscles during rapid exercise
Pyruvic acid + NADH  lactic acid + NAD+

10. Krebs Cycle
When oxygen is available, glycolysis is followed by Krebs and electron transport  this makes up cellular respiration
Aerobic – requires oxygen
In eukaryotes, Krebs takes place inside the mitochondria
Pyruvic acid is broken down into carbon dioxide in a series of energy-extracting reactions

11. Krebs Cycle
Begins when pyruvic acid (from glycolysis) enters the mitochondria
One carbon atom from pyruvic acid becomes part of a carbon dioxide molecule, which is eventually released into the air.
The other 2 carbon atoms from pyruvic acid are used in a series of reactions.
During these reactions, 2 energy carriers accept high-energy electrons  NAD+ is turned into NADH and FAD is turned into FADH2
NADH and FADH2 carry high-energy electrons to ETC

12. Krebs

13. Electron Transport Chain (ETC)
Uses the high-energy electrons from Krebs to convert ADP into ATP
In eukaryotes, it is composed of a series of carrier proteins located in the inner membrane of the mitochondria
In this pathway, high-energy electrons move from one carrier protein to the next.
Their energy is used to move hydrogen ions across the membrane through a protein called ATP Synthase
Each time an ATP Synthase spins, a phosphate group is added to an ADP to make ATP.

14. ETC

15. Energy Totals
In the absence of oxygen, all the energy that a cell can extract from a single glucose is 2 ATP – the product of glycolysis
In the presence of oxygen, the cell can extract much more
Krebs and the ETC allow cell to produce 34 more ATP per glucose
Cellular respiration = 36 ATP total