Anaerobic Respiration

During the last stage of cell respiration, electrons from glucose are passed

down the electron passport chain to the

final electron acceptor, oxygen

Chemiosmosis couples the electron transport

chain to ATP synthesis:

Aerobic Respiration

• When oxygen is the final electron acceptor, the process is called aerobic respiration

• Aerobic = occurring in the presence of oxygen

Anaerobic Respiration

• Some prokaryotes are able to carry out anaerobic respiration, respiration in which an inorganic molecule other than oxygen (O2) is the final electron acceptor.

• For example, some bacteria, called nitrate reducers, can transfer electrons to nitrate (NO3

-) reducing it to nitrite (NO2-).

• Less efficient: usually 30-34 ATPs per glucose molecule.

What happens if there is no available electron acceptor?

Glucose

2 pyruvate

2 ATP

2 ADP 2 NAD+

2 NADH

Aerobic respiration: The NADH then passes its high energy e- to the electron transport chain (becoming NAD+ again) and eventually to O2

Anaerobic respiration: Without O2, NADH has nowhere to donate its e- to, NAD+ cannot be regenerated, and glycolysis stops

glycolysis

Anaerobic fermentation

• Fermentation: An alternative set of reactions that can follow glycolysis in the absence of oxygen as a final electron acceptor.

• Extremely inefficient: no Kreb’s cycle, no ETC. Glycolysis produces a net of 2 ATP’s per glucose molecule

Glucose2

Pyruvate

2 NAD+ 2 NADH

2 ADP 2 ATP

Fermentationby-product

Intermediate accepts electrons from NADH

FERMENTATION PATHWAYS ALLOWS CELLS TO REGENERATE NAD+ FOR GLYCOLSIS

Glucose

2 Pyruvate

2 NAD+ 2 NADH

2 ADP 2 ATP

2 Lactate

Pyruvate accepts electrons from NADH

LACTIC ACID FERMENTATION OCCURS IN HUMANS

During heavy exercise, ATP production will switch from aerobic respiration to

anerobic respiration

Glucose

2 Pyruvate

2 NAD+ 2 NADH

2 ADP 2 ATP

2 Ethanol 2 Acetylaldehyde

2 CO2

ALCOHOL FERMENTATION OCCURS IN YEAST

The Stuff of Life