Fermentation

Anaerobic Alternative to Aerobic Respiration

OK, if you are yeast...

• Making

• 2 ATP from glycolysis is enough

Only catch...

• NAD+ is used up

• So a cell needs a way to regenerate it

They Replenish NAD+

• When yeast and bacteria convert pyruvic acid to CO2 and ethanol (ethyl alcohol).

Alcoholic Fermentation

• “The production of ethanol from glucose”

• Is catalyzed by microbial (bacteria and yeast) enzymes

Yeast Acting on Pyruvic Acid

• Ethanol is released as a waste product O

o

o

o

NAD+

CO2

In Muscle Cells

• Lactic Acid Fermentation

• No CO2 given off

• Eventually carried back to liver to be converted to pyruvic acid

Lactic Acid in Bacteria

• Used in dairy industry to make cheese and yogurt

Strict Anaerobes

• REQUIRE anaerobic (no oxygen) to live

• EXAMPLES: those that live in stagnant ponds and soil

Facultative Anaerobes

• Can make ATP by fermentation either by chemiosmosis or by fermentation, depending whether O2 is present or not

• EXAMPLES: E. coli, yeasts

Why must oxygen be kept out of the wine and beer vats?

• If oxygen is

present, the pyruvic acid will make CO2 and water.

• If oxygen is not present, yeast and bacteria will make ethanol and CO2.