Microbiology, part 23: Metabolism - Lipid & Protein Catabolism

Hi, I'm Cathy with Level Up RN. In this video, I'm going to continue my microbiology review series. Specifically, in this video, I'll be talking about fermentation. And at the end of the video, I'm going to give you guys a little quiz to test your understanding of some of the key points I'll be covering, so definitely stay tuned for that. And if you have our Level Up RN microbiology flashcards, go ahead and pull out your flashcard on fermentation so you can follow along with me.

Fermentation is an anaerobic process that releases energy from organic molecules such as glucose. Fermentation begins with glycolysis, but it does not include the citric acid cycle or the electron transport chain, so only two ATP are generated during glycolysis. The two main types of fermentation that I would be familiar with include lactic acid fermentation and alcohol fermentation. During lactic acid fermentation, pyruvate that was produced in glycolysis is reduced by NADH to form lactic acid. In addition, NADH is oxidized to NAD+, which can be used again in glycolysis to generate more ATP. So one of the main purposes of fermentation is to allow for the regeneration of NAD+ so we can keep producing ATP through glycolysis.

One example of lactic acid fermentation is the production of yogurt by Lactobacillus bacteria. During the fermentation process, the production of lactic acid creates a highly acidic environment, which denatures the proteins in milk, causing it to solidify into yogurt. Lactic acid fermentation also occurs in our muscle cells during times of strenuous exercise, when our respiratory system and cardiovascular system cannot keep up with the oxygen demand, so our muscle cells switch from aerobic respiration to fermentation. So if you are holding a wall squat for a long time and your thigh muscles start to burn, that is lactic acid that you are feeling.

The next type of fermentation we're going to talk about is alcohol fermentation. During alcohol fermentation, pyruvate that was produced in glycolysis is converted into acetaldehyde and carbon dioxide. Acetaldehyde is then reduced by NADH to make ethanol, and NADH is oxidized to NAD+, which can then be used in glycolysis to generate more ATP. And as I mentioned before, one of the main purposes of fermentation is to allow for the regeneration of NAD+ so we can keep producing ATP. Examples of alcohol fermentation include the production of alcoholic beverages, bread, and biofuels. In the case of bread production, when yeast in the bread dough uses alcohol fermentation, carbon dioxide gas is produced, and in turn, this forms bubbles in the bread dough, causing it to expand. And those bubbles leave small holes in the bread as well, which you can see if you look at a slice of bread. As a reminder, I want to emphasize that while fermentation and anaerobic respiration are both anaerobic processes, they are not the same thing. Fermentation only uses glycolysis, whereas anaerobic respiration uses glycolysis, the citric acid cycle, as well as the electron transport chain.

All right. It's quiz time, and I have three questions for you. Question number one. During lactic acid fermentation, blank is reduced by NADH to produce lactic acid. The answer is pyruvate. Number two. During alcohol fermentation, pyruvate produced in glycolysis is converted into blank and blank. The answer is acetaldehyde and carbon dioxide. Number three. How many ATP are produced during fermentation? The answer is two. All right. That's it for this quiz. I hope you did great, and I hope you found this video to be helpful. Take care and good luck with studying.