9.3: Anaerobic Respiration

oxygen’s role in cellular respiration

complete oxidation bc oxygen is the final electron acceptor = net energy captured per glucose 32 ATP and waste products H2O and CO2 = complete cellular respiration

cellular respiration in anaerobic conditions

No oxygen = no final electron acceptor = incomplete oxidation and pyruvate from glycolysis is metabolised by fermentation = waste products lactic acid or ethanol and CO2 and net energy captured per glucose is 2 ATP = less energy than aerobic

fermentation

the metabolic process that converts sugars to acids, gases, or alcohol in the absence of oxygen and without cellular respiration, producing a small amount of energy.

what does fermentation involve

glycolysis and reactions that regenerate NAD+ by transferring electrons from NADH to pyruvate. NAD+ reused to oxidise sugar by glycolysis which nets 2 ATP

NAD+

a coenzyme that carries electrons and used for oxidation reactions that form carbon–oxygen double bonds

different types of fermentation

alcohol (yeast and bacteria) and lactic acid (animals)

lactic acid fermentation

Converts sugars into ATP and lactic acid - in muscle cells during intense exercise. Go through glycolysis but opposed to pyruvate moving into mitochondria into 2nd stage of cellular respiration, the pyruvate instead undergoes transformation into lactate by lactate dehydrogenase

• C6H12O6 + 2 ADP + 2 Pi --> 2 lactate + 2 ATP

alcoholic fermentation

Converts sugars into ethanol in 2 steps:

1st - CO2 released from pyruvate is converted into acetyl aldehyde. 2nd - acetyl aldehyde is reduced by NADH to ethanol = regenerates NAD+ needed for continuation of glycolysis

• C6H12O6 + 2 ADP + 2 Pi --> 2 ethanol + 2CO2 + 2 ATP

disadvantage of fermentation

cellular respiration yields more energy (32 compared to 2) and glucose is only partially oxidised so more energy remains in the products than in CO2 = fermentation less efficient