Anaerobic Cellular Respiration SBI4U

Under low oxygen conditions pyruvate oxidation, Krebs cycle and ETC cannot occur.

In Humans Under low oxygen conditions, NADH produced in glycolysis transfers hydrogen atoms to pyruvate in the cytoplasm producing lactate (lactic acid) and NAD+. The NAD+ is reused in glycolysis.

Lactic Acid... Causes stiffness and fatigue in muscles. When vigorous exercise stops, lactic acid is oxidized back to pyruvate and it can then enter pyruvate oxidation and the rest of aerobic CR can occur When you “pant” after strenuous exercise this is considered the body’s way of “paying the O2 debt”

Lactic Acid Build Up 2 Lactate (C3H6O3) + 6O2 -----------> 6 CO2 + 6H2O Build up of lactic acid in muscle cells causes the pH of the cell to decrease  this will effect every enzyme in the cell It can also cause the muscle cells to swell due to an influx of water due to osmosis As soon as oxygen levels increase, the body will metabolize lactic acid and clear it from the cell Too much lactic acid build up = muscle fatigue Gluconeogenesis (in liver) 2 lactate (C3H6O3) + energy (from 16 ATP) ---> glucose (C6H12O6)

In Yeast Some organisms do not perform the last 3 stages of CR, but rather function best under low O2 conditions.

In Yeast Acetaldehyde is formed in yeast when CO2 is removed from pyruvate by the enzyme pyruvate decarboxylase A H+ from NADH is transferred to acetaldehyde to make ethanol.

Alcohol Fermentation Pyruvate decarboxylase The 2 ATP molecules produced during glycolysis are enough to satisfy the organisms energy needs, ethanol and CO2 are waste products.

Ethanol fermentation Ethanol fermentation carried out by yeast is used by humans to: Bake: live yeast is added to baking, the yeast break down the glucose found in starch (from the flour) and release CO2, the bubbles of gas cause the baking to rise.

Ethanol Fermentation Alcohol: yeast are used to make beer, wine and other alcohols.