Aerobic cellular respiration No O 2 present

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Chapter 7
Anaerobic Respiration and
Fermentation
Anaerobic respiration
• Anaerobic respiration uses molecule other
than O2 as the final electron acceptor in the
electron transport chain.
• Only prokaryotes can respire anaerobically.
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Concept 7.5
• Without O2, the electron transport chain will
cease to operate*. If the electron transport chain
is not operating, glycolysis couples with
fermentation to produce ATP.
• Two common types are alcohol fermentation and
lactic acid fermentation.
© 2014 Pearson Education, Inc.
Figure 7.16a
2 ADP  2 P
Reactants
Glucose
i
2 ATP
Glycolysis
2 Pyruvate
2 NAD
2 NADH
2
2 ADP  2 P
Glucose
2 ATP
i
Glycolysis
2 Pyruvate
2 NAD
2 Ethanol
(a) Alcohol fermentation
2 NADH
 2 H
2 CO2
2 Acetaldehyde
Figure 7.16b
2 ADP  2 P
Glucose
2 ATP
i
Glycolysis
2 NAD
2 NADH
 2 H
2 Pyruvate
2 Lactate
(b) Lactic acid fermentation
Comparing Fermentation with Anaerobic and Aerobic
Respiration
• All use glycolysis (net ATP  2) to oxidize glucose
and harvest chemical energy of food.
• In all three, NAD is the oxidizing agent that accepts
electrons during glycolysis.
• The processes have different final electron
acceptors: an organic molecule (such as pyruvate or
acetaldehyde) in fermentation and O2 in cellular
respiration.
• Cellular respiration produces 32 ATP per glucose
molecule; fermentation produces 2 ATP per glucose
molecule.
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• Obligate anaerobes carry out only fermentation or
anaerobic respiration and cannot survive in the
presence of O2.
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facultative anaerobes
CYTOSOL
Glucose
Glycolysis
Pyruvate
No O2 present:
Fermentation
O2 present:
Aerobic cellular
respiration
MITOCHONDRION
Ethanol,
lactate, or
other products
Acetyl CoA
Citric
acid
cycle
The Evolutionary Significance of Glycolysis
• Very little O2 was available in the atmosphere until
about 2.7 billion years ago
Figure 7.18-5
Proteins
Carbohydrates
Amino
acids
Sugars
Fats
Glycerol Fatty
acids
Glycolysis
Glucose
Glyceraldehyde 3- P
NH3
Pyruvate
Acetyl CoA
Citric
acid
cycle
Oxidative
phosphorylation
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