Anaerobic Energy-Releasing Pathways

AP BiologyFall 2010

Anaerobic pathways operate when oxygen is absent (or limited)

Pyruvate from glycolysis is metabolized to produce molecules other than acetyl-CoA

Organisms that carry out fermentation (fermentors) are diverseMany die when exposed to oxygenOthers use oxygen but switch when it

becomes scarce Fermentation yields enough energy for

many single-celled anaerobic organisms Sufficient for some aerobic cells when

oxygen levels drop Insufficient for large, multi-celled

organisms

Lactose fermenting bacteria turn bright pink!

Fermentation begins with glucose degradation to pyruvate

Cellular enzymes convert pyruvate to acetaldehyde, which then accepts electrons from NADH to become alcohol

Yeasts are valuable in the backing industry and in alcoholic beverage production Carbon dioxide by-product makes dough

“rise”

Certain bacteria (as in milk) and muscle cells have the enzymes capable of converting pyruvate to lactate

No additional ATP beyond the net two from glycolysis is produced

NAD+ is regenerated

When muscle cells are very active, they convert to producing lactate temporarily

Slow stitch muscle fibers (dark red) Support steady, prolonged activity because

they have many mitochondria making large quantities of ATP

Fast twitch muscle fibers (light colour) have few mitochondria and produce small amounts of ATP by lactate fermentationSupporting quick, non-sustained demands

for energy

1. T/F Yeast is used in bread making because it produces carbon

dioxide2. T/F In lactate fermentation FAD is

regenerated 3. T/F Fast twitch muscles are dark red

and support steady, prolonged material

1. True2. False NAD+ is regenerated 3. False This describes slow twitch

muscles