 Hey everybody, Dr. O here. Let's talk about fermentation. Actually, before we jump into fermentation, just want you to understand that we've already covered aerobic respiration start to finish and how you can generate that 36 to 38 ATPs. Many organisms use something other, some other inorganic substance other than oxygen as their final electron acceptor, as you can see here, and they're going to use what's called anaerobic respiration. So I won't go into detail here, but they don't have quite the concentration gradient or electrochemical gradient that we have when we use oxygen. So they can't generate as much ATP. As you see here, the totals for anaerobic respiration are between five and 36, depending on the electron acceptor. Here's a couple of quick examples here. I think the nitrate and nitrite using denitrifying organisms in the soil are very important. So they take nitrogen and change its form in the soil. So it's other examples of where it's important. Another example that's relevant in microbiology, bacteria like E. coli, if oxygen's not available, can switch and start using the nitrate as a final electron acceptor. That's why we have bacteria that are called facultative anaerobes. They prefer oxygen, so they grow better in its presence, but they can switch their metabolism and grow OK without oxygen as well. So there's a couple of quick things there, but let's focus in on fermentation here. So fermentation is when you use an organic final electron acceptor. It's usually going to be pyruvate. So where would you get pyruvate from glycolysis? So these fermenters are still going to use anaerobic glycolysis. The fermentation process takes that pyruvate and changes it, but doesn't actually generate any more energy. So the reason that you do it, and I'll show you the path in just a moment here, but why would we undergo fermentation? What do we need to do with this pyruvate? So let's go ahead and let me show you, but you see the numbers here real quickly. Fermentation is only going to release those two ATP directly that come from glycolysis. But here's an example of lactic acid fermentation where you convert glucose to pyruvate using glycolysis, exactly like we talked about before. Net gain of two ATP and you have those two NADHs produced. So why would you go on? What fermentation does as it turns pyruvate into lactate or lactic acid in this situation is liberates those NAD pluses. So here's the key to note. Fermentation doesn't generate any more ATP directly, but without it, we'd run out of NAD plus and we couldn't undergo glycolysis. So that fermentation step isn't to generate energy directly, it's to keep glycolysis going and that's why you do it. And here's the thing, so we have, obviously we have ethanol fermentation, there's lots of kinds of fermentation, but in this class, lactic acid fermentation is the most important one. And that's because we use lactic, this is how we produce lactate in our bodies, in our muscles, if we don't have enough oxygen. So we've already covered that. Without oxygen, we turn pyruvate into lactic acid. But think about like the microbes that do this as well. You have, so the same process would happen in a bacteria that's going to turn milk into yogurt or cheese. So what happens here is, when fermenters get a hold of your milk, they drop the pH and that's what causes the curdling and that's what turns milk into a solid, something like yogurt or cheese. So it's going to be important in our food, but it's also going to be important into our health as well. And that's because we want a lot of lactic acid fermenters inside our body. So you think about the lactic acid fermenters that are in your gut. They keep the pH low and that inhibits the growth of pathogenic bacteria. We've talked about that. So that's why your probiotics are dominated by lactic acid producers like lactobacillus and befitus. So we want these bacteria keeping the pH in our gut low to inhibit the growth of pathogens, pathogens don't like low pHs. That's why sauerkraut is, if you have sauerkraut for a year, it's still probably safe to eat whereas you wouldn't want cabbage sitting around for a year and then eat it. The low pH is what protects or preserves that food. This is even more important in the vaginal microbiome. When you have, we always talk about the microbiome, a key being diversity. So most microbiomes are going to be, you want them to be very diverse, not the vaginal microbiome. You want a minimum of 70% of the microbes in the vaginal microbiome to be lactic acid producers keeping the pH low and that's what keeps the bacterial infections and those types of things away. All right, so those are two reasons why lactic acid fermentation is very important to our health from a microbiological standpoint. Last key thing I want to note here then is where does the energy go? So when we're done fully oxidizing glucose, we've taken all the energy. We generated those 36 or 38 ATP. So oxidative phosphorylation, aerobic respiration steals all the energy, leaving low energy or useless end products. Fermentation takes only a tiny bit of energy away, which means the end product still have the energy. So I was like to say that respiration leaves useless end products. Fermentation leads useful end products. Let's go ahead and take a look at some examples here. I'm just going down the right hand side. We have commercial solvent, things like acetate. Gas alternatives like ethanol, beer, bread, wine, butter, sauerkraut, yogurt, cheese. Some pharmaceuticals use mixed acid fermentation. Swiss cheese is separate. Swiss cheese is going to use a different organism. But still, as you see, these end products are very, very useful. So with fermentation, you take pyruvate and you turn it into some amazingly useful end product. Like I'm a big fan of cheese. I'm sure some people are bigger fans of alcohol, but I'll take cheese any day. So that's kind of the cool thing about fermentation. So fermentation, they only get a little bit of energy. They do fermentation in order to keep glycolysis running. That's why fermentation matters. But for us, we can get very useful end products out of fermentation. And we've been doing this for thousands of years as humans, borrowing microbial fermentation for our food. And now we have gas alternatives, et cetera. I think that's kind of cool. All right, so that's fermentation in a nutshell. I hope that helps. Have a wonderful day. Be blessed.