17.3.4: Anaerobic Respiration (keep but move to 9.2?)

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Conditions without oxygen are referred to as anaerobic. In this case, the pyruvate will be converted to lactate in the cytoplasm of the cell as shown below.

Figure 6.281.png

Figure 9.2.2.2.1 Pyruvate fork in the road, what happens depends on whether it is aerobic or anaerobic respiration¹

What happens if oxygen isn't available to serve as the final electron acceptor? As shown in the following video, the ETC becomes backed up with electrons and can't accept them from NADH and FADH₂.

Web Link

Video: What happens when you run out of oxygen? (0:37)

This leads to a problem in glycolysis because NAD is needed to accept electrons, as shown below. Without the electron transport chain functioning, all NAD has been reduced to NADH and glycolysis cannot continue to produce ATP from glucose.

Figure 6.282.png

Figure 9.2.2.2.2 Why NAD needs to be regenerated under anaerobic conditions²

Thus, there is a workaround to regenerate NAD by converting pyruvate (pyruvic acid) to lactate (lactic acid) as shown below.

Figure 6.283. .png

Figure 9.2.2.2.1 3. The conversion of pyruvic acid to lactic acid regenerates NAD^3,4

However, anaerobic respiration only produces 2 ATP per molecule of glucose, compared to 32 ATP for aerobic respiration. The biggest producer of lactate is the muscle. Through what is known as the Cori cycle, lactate produced in the muscle can be sent to the liver. In the liver, through a process known as gluconeogenesis, glucose can be regenerated and sent back to the muscle to be used again for anaerobic respiration forming a cycle as shown below.

Figure 6.284.png

Figure 9.2.2.2.4 The Cori cycle⁵

It is worth noting that the Cori cycle also functions during times of limited glucose (like fasting) to spare glucose by not completely oxidizing it.

Contributors

Brian Lindshield and Claudia Kelley

References & Links

simple.Wikipedia.org/wiki/Mi..._en_(edit).svg
en.Wikipedia.org/wiki/File:CellRespiration.svg
en.Wikipedia.org/wiki/Pyruvi...D-skeletal.png
en.Wikipedia.org/wiki/Lactic...d-skeletal.svg
commons.wikimedia.org/wiki/F...iCycle-eng.svg

Video

What happens when your run out of oxygen? - http://www.youtube.com/watch?v=StXlo1W3Gvg