Anaerobic Respiration also called Fermentation Respiration without oxygen

Anaerobic Respiration (also called Fermentation)

• Respiration without oxygen as the electron acceptor • Electrons are not passed down the electron transport chain across the cristae • NADH and FADH 2 are not oxidized • Alternative system which will allow glycolysis to continue despite the lack of oxygen. • During anaerobic fermentation, hydrogens and electrons are removed from NADH and the end product pyruvate is still formed.

Two different anaerobic fermentation pathways • Alcoholic Fermentation • Lactic Acid Fermentation

Alcoholic fermentation • common in bacteria and yeast cells. • Pyruvate is first decarboxylated to yield a 2 -carbon substance acetaldehyde. • Acetaldehyde is then reduced as hydrogens are transferred from NADH to acetaldehyde to produce ethyl alcohol. Yeast cells Anaerobic bacteria

CO 2 (from glycolysis) + 4 ATP (Electron removed) *Net 2 ATP per glucose

• Obligate anaerobes These organisms do not use oxygen and will die in the presence of oxygen. • Facilitative anaerobes These organisms can survive with and without oxygen, they can utilize aerobic and anaerobic metabolic pathways.

Lactic Acid Fermentation • In animal cells when oxygen is reduced or absent. Also in some bacteria, such as lactobacillus ( causes tooth decay) • Pyruvate is used as the direct acceptor of the hydrogens removed from NADH. • The end product is a molecule of lactic acid. Lactic acid [or lactate] is a common by-product of anaerobic respiration in muscle cells. • Lactic acid is broken down by the liver back to pyruvate or also to water and CO 2

(from glycolysis) *Net 2 ATP per glucose + 4 ATP

• The steps of anaerobic fermentation do not themselves produce any additional ATP. Their sole value is that, by permitting the continued glycolytic activity, they allow at least some energy to be recovered in the absence of oxygen.