Anaerobic Respiration

Anaerobic Respiration – Fermentation Oxygen is not needed directly for the matrix reactions (Krebs Cycle & Pyruvate Oxidation). However, if oxygen is not present to accept electrons at the end of the ETC – NADH cannot be oxidized by NADH Dehydrogenase. Thus, no NAD+ is being made to oxidize the molecules coming from glucose. Organisms need a way to generate ATP in the absence of oxygen – at least temporarily. This is achieved by recycling the NAD+ used to oxidize the molecules in glycolysis. This is referred to as fermentation. The only goal of fermentation is to produce NAD+, and allow glycolysis to continue. ALCOHOL FERMENTATION Alcohol fermentation is done by yeast and some kinds of bacteria. These microorganisms convert sugars in ethanol and carbon dioxide. Alcoholic fermentation begins after glucose enters the cell. The glucose is broken down into pyruvate. Pyruvate is then converted to CO2, and Acetaldehyde (2C). This 2 Carbon molecule then receives electrons from NADH, becoming ethanol, and allowing NADH to be oxidized into NAD+.

Lactic Acid Fermentation Many organisms will also ferment pyruvate into, other chemicals, such as lactic acid. Humans ferment lactic acid in muscles where oxygen becomes depleted, resulting in localized anaerobic conditions. This lactic acid causes the muscle stiffness someone may feel after exercise programs. The stiffness goes away after a few days since the cessation of strenuous activity allows aerobic conditions to return to the muscle, and the lactic acid can be converted into ATP via the normal aerobic respiration pathways.