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Anaerobic respiration
• Anaerobic respiration uses molecule other than O2 as the final electron acceptor in the electron transport chain.
• Only prokaryotes can respire anaerobically.
© 2014 Pearson Education, Inc.
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 2 ATPPi
Glucose Glycolysis
2 Pyruvate
22 NADH2 NAD
Reactants
2 ADP 2 2 ATPPi
Glucose Glycolysis
2 Pyruvate
2 CO22 NADH
2 H
2 NAD
2 Ethanol
(a) Alcohol fermentation
2 Acetaldehyde
2 ATP
Figure 7.16b
2 ADP 2 2 ATPPi
Glucose Glycolysis
2 Pyruvate
2 NADH 2 H
2 NAD
(b) Lactic acid fermentation
2 Lactate
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. © 2014 Pearson Education, Inc.
• Obligate anaerobes carry out only fermentation or anaerobic respiration and cannot survive in the presence of O2.
© 2014 Pearson Education, Inc.
Glucose
CYTOSOLGlycolysis
Pyruvate
O2 present:
Aerobic cellular respiration
No O2 present:
Fermentation
Ethanol,lactate, or
other products
Acetyl CoA
Citricacidcycle
MITOCHONDRION
facultative anaerobes
The Evolutionary Significance of Glycolysis
• Very little O2 was available in the atmosphere until about 2.7 billion years ago
Figure 7.18-5Proteins
Aminoacids
Carbohydrates
Sugars
Glucose
Glycolysis
Glyceraldehyde 3-
Pyruvate
P
Acetyl CoA
Citricacidcycle
NH3
Fats
Glycerol Fattyacids
Oxidativephosphorylation