Fermentation
H. Biology
Ms. Kim
Fermentation
• Fermentation enables some cells to
produce ATP without the use of oxygen
(O2)
• Cellular respiration
–Relies on oxygen to produce ATP
• In the absence of oxygen
–Cells can still produce ATP through
fermentation
Cellular respiration vs. fermentation
Oxygen Present →
Aerobic Respiration
(efficient!)
Oxygen NOT Present →
Fermentation (not
efficient)
Respiration = 66% efficient
Fermentation = 3.5% efficient
Fermentation
• If there is no oxygen present (anaerobic) the
pyruvate (from glycolysis) goes to fermentation
• The main goal of fermentation is:
– To make NAD+ to put back into glycolysis
– This makes NO ATP on its own (it just keeps glycolysis
going so that it can make 2 ATP at a time)
• Occurs in the cytosol
• 2 types of fermentation
– 1) Alcohol
– 2) Lactic acid
• Glycolysis
–Can produce ATP with or
without oxygen, in aerobic or
anaerobic conditions
–Couples with fermentation to
produce ATP
Types of Fermentation
• Fermentation consists of
– Glycolysis plus reactions that regenerate
NAD+, which can be reused by
glyocolysis
Alcohol Fermentation
• Pyruvate is converted to ethanol (ethyl
alcohol) in two steps, one of which
releases CO2
• Ex: bacteria and yeast
• In alcohol fermentation
–Pyruvate is converted to
ethanol (ethyl alcohol) in two
steps, one of which releases
CO2
GLUCOSE  Pyruvate  Ethanol and CO2
• Ex: bacteria and yeast do this
Alcoholic Fermentation
- Pyruvate is turned
into ethanol
- CO2 is released
(bubbles!)
- Done by yeast for
brewing
Remember: Goal is to produce NAD+ to
send back to glycolysis so it can keep
going and produce more ATP
3C Pyruvate → 2C Ethanol
Lactic Acid Fermentation
• During lactic acid fermentation
–Pyruvate is reduced directly to NADH
to form lactate as a waste product
–NO CO2 is released
• Ex #1: fungus and bacteria in dairy industry
to make cheese/ yogurt
• Ex #2: Human muscle cells
Lactic acid
fermentation
3C Pyruvate → 3C Lactate
- Pyruvate is turned into
Lactate (or lactic acid)
- Lactate is eventually
carried away by the blood
to the liver where it gets
converted back into
pyruvate
- Example: Muscle Cells
- The lactic acid is what
makes your muscles sore
after lifting or intensive
exercise
- No CO2 is released
Remember: Goal is to produce
NAD+ to send back to glycolysis
so it can keep going and produce
more ATP
Lactic acid vs. alcohol
fermentation
Similarities:
1. Both start with pyruvate from
glycolysis
2. Both create NAD+ to be sent
back to glycolysis
3. Neither make any ATP on their
own
Differences:
1. Lactic acid is made and does
NOT give off CO2
2. Alcohol makes ethanol and
gives off CO2
Fermentation - Overview
Obligate Aerobes →
needs oxygen; can do
respiration only
Obligate Anaerobes →
can’t have oxygen;
fermentation only
Facultative Anaerobes
→ can live with or
without oxygen; prefer
oxygen b/c more
efficient
Respiration is 19 times more efficient than
fermentation (38 ATP vs. 2 ATP)
P1
2 ADP + 2
Glucose
2 ATP
O–
Glycolysis
C
O
C
O
CH3
2 Pyruvate
2 NADH
2 NAD+
H
H
C
C
OH
2 Acetaldehyde
(gets reduced by NADH. It is
the oxidizing agent.)
(a) Alcohol fermentation
2 ADP + 2
Glucose
C
P1
2 ATP
Glycolysis
2
O
C
O
CH3
2 Ethanol
H
CO2
H
CH3
NO
CO2
made
2
NAD+
O
OH
CH3
2 Lactate
(b) Lactic acid fermentation
O–
2 NADH
C
O
C
O
CH3
2 Pyruvate
(gets reduced by NADH. It is
the oxidizing agent.)
Fermentation and Cellular
Respiration Compared
• Both fermentation and cellular respiration
– Use glycolysis to oxidize glucose and other
organic fuels to pyruvate
• Fermentation and cellular respiration
– Differ in their final electron acceptor
• Cell respriraition uses O2
• Fermentation uses NAD+
• Cellular respiration
– Produces more ATP (~36-38 ATP)
• Fermentation
– Produces 2 ATP per cycle
Exit Slip
1) Alcoholic fermentation
converts glucose to
2) Alcoholic fermentation is
utilized by what organisms?
3) Lactic acid fermentation
converts glucose to
4) Lactic acid fermentation is
utilized by what organisms?
5) What is the final acceptor for
alcoholic fermentation?
6) What is the final acceptor for
lactic acid fermentation?
7) What is the final acceptor for
cellular respiration?
8) Draw and label the
diagram