Transcript Fermentation

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
NAD+
o
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.