Anaerobic Respiration Process

Study Notes

Bacteria can use electron transport chains with exogenous electron acceptors other than oxygen, such as nitrate, sulphate, or carbon dioxide, which is less efficient in producing ATP due to less positive reduction potentials.
Facultative anaerobes, like enteric bacteria, can use nitrate as a terminal acceptor in the absence of oxygen, while obligate anaerobes cannot use oxygen at all.
Methanogens, which use carbon dioxide or carbonate as electron acceptors, reduce carbon dioxide to methane.

Replenishment of NAD+ and FAD+ is necessary to prevent glycolysis from stopping.

The second stage of metabolism involves the breakdown of glucose to pyruvate or acetyl-CoA through glycolytic pathways, including the Embden-Meyerhof-Parnas (EMP) pathway, pentose phosphate pathway, and Entner-Doudoroff pathway.
The EMP pathway is the most common and takes place in the cytoplasm of bacteria.

The Entner-Doudoroff pathway is used in a few bacteria, such as Pseudomonas spp. and some Gram-positive bacteria, and can operate aerobically or anaerobically.
It can occur simultaneously with the glycolytic and pentose phosphate pathways and is important in biosynthesis.

The third stage of metabolism involves aerobic, anaerobic respiration, and fermentation.
Pyruvate can be oxidized to carbon dioxide and acetyl-CoA, which can enter the TCA cycle.

Aerobic respiration releases the most energy in the form of ATP when pyruvate is degraded to carbon dioxide.
Acetyl-CoA enters the TCA cycle, which is functional in many aerobic bacteria, free-living protozoa, and most algae and fungi.
The TCA cycle provides carbon skeletons for biosynthesis.

The TCA cycle produces carbon dioxide, ATP, NADH, and FADH.
Most ATP is generated when NADH and FADH are oxidized in the electron transport chain.
The TCA cycle and electron transport result in a net energy gain of 38 ATP per glucose molecule.