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Lactic Acid & Alcoholic Fermentation: Comparison, Contrast & Examples

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  • 0:05 Fermentation
  • 1:33 Review of Aerobic…
  • 3:15 Lactic Acid Fermentation
  • 4:33 Alcoholic Fermentation
  • 5:25 Lesson Summary
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Lesson Transcript
Instructor: Kristin Klucevsek

Kristin has taught college Biology courses and has her doctorate in Biology.

When in an anaerobic environment, some cells can use glycolysis and fermentation to keep producing ATP. Lactic acid fermentation happens in our muscle cells when we are exercising feverishly, while alcoholic fermentation is used in yeast cells and is what leads to beer, bread, and wine.

Fermentation

Playing on a local basketball league can be an excellent time. Good times, good friends, good sportsmanship - but also lots of hard work and exercise. Perhaps you celebrate a win at a local pub with your teammates. Team celebrations are also an excellent part of being in a local league. As you toast your victory beer to your friends, you notice your arms are also sore from all those free throws. Make no mistake - you worked hard today. Your team deserved that win. There were plenty of times that you were up and down the court, completely out of breath, but somehow you found the energy to just keep on going.

That reminds us... so, did you know that your mug of beer and your effort on the basketball courts actually have something in common? Both the energy you spent playing the game and the alcohol in your beer are byproducts of a similar biological process - fermentation. Now that's a little extra something to think about as you enjoy your beer. In this lesson, we'll explain just what we mean.

See, your body's cells normally undergo aerobic cellular respiration, or a process that uses oxygen to convert food into energy. However, there are times when cells undergo anaerobic cellular respiration, or a process that does not use oxygen to convert food into energy. Your muscles' cells, when deprived of air, will use anaerobic cellular respiration. Yeast, which is an organism used to make beer and wine, will follow a similar pathway when deprived of oxygen, too.

Process of aerobic cellular respiration
Aerobic Cellular Respiration

Review of Aerobic Cellular Respiration

Before we delve into how this process works, let's first review cellular respiration as a whole. Remember that in aerobic cellular respiration, there are three stages: glycolysis, the citric acid cycle, and the electron transport chain. In glycolysis, a net of two molecules of ATP, or chemical energy, are produced. The citric acid cycle produces another two molecules, while the electron transport chain produces a whopping 28 molecules of ATP. Oxygen is used in aerobic cellular respiration as the final electron acceptor in the electron transport chain, which is part of why it's able to create so much ATP.

But what happens when oxygen doesn't exist? Like when you're running so hard that you can't catch your breath during the game? The electron transport chain can then no longer be used because there's a shortage of oxygen. Instead, in anaerobic cellular respiration, the only step of this process that occurs is glycolysis. This is unfortunate because ATP is like the chemical currency of the cell, and we lose the ability to 'pay' for all the cellular processes when we run out of ATP. Glycolysis only provides two molecules of ATP. By skipping the final two steps of this process, we lose out on a lot of cash.

However, sometimes some energy is better than no energy at all. Therefore, in anaerobic conditions, some organisms perform fermentation, which is a process that anaerobically generates ATP by performing glycolysis and one extra step. There are two types of fermentation we'll discuss in this lesson - lactic acid fermentation and alcoholic fermentation.

Lactic Acid Fermentation

Glycolysis occurs in the cytosol. Along with 2 ATP, it also produces 2 NADH + H+ electron carriers and two 3-carbon pyruvate molecules. Normally the pyruvate molecules would continue on to the citric acid cycle, while the electron carriers would continue on to the electron transport chain. Here, these electron carriers would drop off their electrons and become oxidized back to NAD+. Then NAD+ molecules would be able to return to glycolysis to perform cellular respiration all over again. But when there is no electron transport chain to go to, what is a poor electron carrier to do with its electrons?

The process of lactic acid fermentation
Lactic Acid Fermentation Process

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