Chapter 7Anaerobic 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.

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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.

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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