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Understanding Anaerobic Pathways: From Fermentation to Oxygen Debt

Explore the anaerobic pathways in cells, from glycolysis to ethanol and lactate fermentation. Learn how NADH is oxidized, and delve into the concept of oxygen debt and VO2 max. Discover the crucial processes that sustain cellular energy production in the absence of oxygen.

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Understanding Anaerobic Pathways: From Fermentation to Oxygen Debt

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  1. ANAEROBIC PATHWAYS • NAD+ is in limited supply, so if the cell does not have a way to oxidize the NADH back to NAD+ glycolysis will come to a halt. • The ETC oxidizes NADH to NAD+ when oxygen is present. Eukaryotic organisms have two primary means of oxidizing NADH when oxygen is not present. Bacteria have developed tons of methods. • These processes are called fermentation. • Glycolysis occurs and glucose is broken down into 2 pyruvate, 2 NADH + 2H+, and 2 ATP (net). • Then:

  2. ETHANOL FERMENTATION (yeast cells) • Pyruvate is immediately decarboxylated into acetylaldehyde (CH3COH) • NADH is then oxidized back into NAD+ and the protons (H+) turn acetylaldehyde into ethanol. • Still only a net of 2ATP.

  3. LACTATE FERMENTATION (animal cells) • Pyruvate is immediately reduced by NADH (NADH is oxidized into NAD+) to form lactate • Lactate (lactic acid) is thought to cause muscle pain and stiffness, but current research suggests it is just a correlation • Oxygen debt is the amount of oxygen required to catabolize lactate into carbon dioxide and water. • Lactic acid is transported to the liver and is oxidized back into pyruvate when the oxygen debt is repaid.

  4. VO2 max • The maximum volume of oxygen that the cells of the body can remove from the bloodstream while the body experiences maximal exertion (mL/kg/min) • Measures the body's capacity to generate the energy required for physical activity • Higher VO2 values are associated with higher aerobic fitness (see Table 2 and 3, pg 122) • Average ~35 mL/kg/min, Elite athlete ~70 mL/kg/min • Lab Activity 2.3.4 p. 131 Estimating VO2 max (a less intense, inexpensive way to estimate your VO2 max).

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