1. FERMENTATION

2. Calling all NAD+ please!
Glycolysis allows organisms to obtain energy from nutrients in the absence of oxygen
Step 6 in the glycolytic pathway reduces NAD+ to NADH
However, cells possess a limited supply of NAD+
If glycolysis continues without a mechanism to oxidize NADH back to NAD+, step 6 would be blocked and glycolysis would STOP
In aerobic respiration, the ETC oxidized NADH allowing glycolysis to continue

3. Oh give me another way…
Organisms have several ways of recycling NAD+ and allowing glycolysis to continue when oxygen is not available
One method involves the transfer of the hydrogen atoms of NADH to certain organic molecules instead of the ETC
This process is known as fermentation

4. Fermentation Eukaryotes use 2 methods of fermentation
Ethanol fermentation
Lactic acid (lactate) fermentation

6. Ethanol Fermentation

7. Ethanol Fermentation: The Process
Some bacteria, yeast, mold, etc.
NADH from glycolysis passes its hydrogen atoms to acetaldehyde, a compound formed when CO2 is removed from pyruvate by pyruvate decarboxylase
Acetaldehyde is reduced to form ethanol, oxidizing NADH to NAD+ so it can return back to glycolysis and glycolysis can continue

8. Ethanol Fermentation
The 2 ATP molecules produced in glycolysis satisfy the organisms energy needs and the ethanol and CO2 are released as waste products
Humans use these waste products to produce breads, pastries, wine, beer, liquor, etc.

9. Lactic Acid Fermentation

10. Lactic Acid Fermentation
During strenuous exercise, muscles respire glucose faster than oxygen can be supplied
Under these conditions, oxidative respiration slows down and lactic acid fermentation begins

11. Lactic Acid Fermentation: The Process
NADH produced in glycolysis transfers its hydrogen atoms to pyruvate
This produces lactic acid and regenerates NAD+
Lactic acid is transported through the blood stream from the muscles to the liver
When vigorous exercise ceases the lactic acid is oxidized back to pyruvate which will again start aerobic respiration

12. Homework
Section 4.4 p
Answer p , 7, 8