Fermentation - Video Tutorials & Practice Problems
On a tight schedule?
Get a 10 bullets summary of the topic
concept
Fermentation
Video duration:
6m
Play a video:
Video transcript
The fate of pyruvate is then determined by what type of conditions our cell is performing glycolysis under and also what type of cell we have. If we have anaerobic conditions in our cells as humans, we are going to generate lactate. If we have anaerobic or hypoxic meaning not a lot of oxygen conditions and or yeast for example, we're actually going to make ethanol and carbon dioxide and and this is actually the basis for making things like beer. Very important process in human history, fermentation of alcohol. It's actually one of the reasons that some people, some anthropologists believe humans organized into societies but that's a whole other story. And, lastly, if we have aerobic conditions, our pyruvate is going to be turned into Acetyl CoA and that's what we're going to talk about, in the next unit when we get into aerobic cellular respiration. For now, let's talk about fermentation. So, alcohol fermentation, let's talk about that first because, well, it's a subject near and dear to my heart. As someone who has, brewed beer in the past. It's very fun, super awesome, process that relies on organisms to actually carry out these reactions. Super cool. On organisms to actually carry out these reactions. Super cool. Alright. So basically, what we have on top is the short version of glycolysis, right? We start out with our 6 carbon, glucose. We make our 3 carbon pyruvate. And in the process, we're going to generate a net of 2 ATP and 2 NADH. And the whole point of fermentation is that in the absence of oxygen, we can't use that NADH to, fuel oxidative phosphorylation. So, we have to do something with it because we need more NAD plus to keep glycolysis going. There's not just infinite NAD plus in a cell and so the cell has to take that NADH, do something with it to make more NAD+o regenerate NAD+o. It needs to oxidize NADH and so fermentation is the way our cells accomplish that. And again, the whole point is to sustain glycolysis in the absence of oxygen and it's worth noting that actually some cells only do fermentation. Our red blood cells for example, only carry out glycolysis. So they rely on fermentation in order to keep glycolysis going. Now, of course, our red blood cells don't do alcohol fermentation. Otherwise, we'd all get drunk when we go for a run and obviously that doesn't happen. We do lactic acid fermentation which we're going to get to in a second. So, in alcohol fermentation, here's our pyruvate. What's going to happen is we are going to decarboxylate our pyruvate and remember, our carbon numbering here is 3 or 4, 25, and 1 or 6. And we're going to decarboxylate this group right here, right? So the CO2 that's leaving, that's that carbon is either carbon 3 or carbon 4 from glucose. What we're left with is a molecule called, acetaldehyde. Acetaldehyde is going to contain carbon 2 or 5 and carbon 1 or 6 and this molecule is currently somewhat oxidized, right? We have a carbonyl there. It's going to get reduced by NADH. And remember, of course, we have we have, 2 NADH and we have 2 of these molecules for every one glucose we put in. And it's going to get reduced to ethanol. Oops, I wrote ethanol. Ethanol and just to be crystal clear, that's carbon 2 or 5 and that's carbon 1 or 6. So that's alcohol fermentation and the whole point is to recycle NAD plus so that we can continue glycolysis. Now, let's take a look at lactic acid fermentation or what's known as the Cori cycle, named after the guys who discovered it. And here, pyruvate is actually going to be direct, directly reduced by NADH to form lactate and NAD plus So again, we have our 1 glycolysis I'm sorry, 1 glucose go through glycolysis, make a net two ATP, two NADH NADH and we're going to have 2 pyruvates. Numbering is same as above. And here, NADH is going to directly reduce this molecule to lactate this molecule. This is lactate and that's going to regenerate NAD plus and you can see we're reducing this carbonyl here and the numbering stays the same. So, our numbering hasn't changed. We have 3, 4, 2, 5, and 16. And again, the whole point of fermentation is just to keep glycolysis going by regenerating NAD plus Alright. With that, let's turn the page.