Glycolysis: ATP Production and NADH Generation in Cells

Glycolysis occurs in both eukaryotic and prokaryotic cells, yielding ATP and NADH as electron carriers.

### Understanding Glycolysis: The Initial Stage of Cellular Respiration
* 🔬 Glycolysis is the **first step of cellular respiration**, occurring in both eukaryotic and prokaryotic cells, and takes place in the **cytoplasm**.
* ⚙ The multi-step process of glycolysis involves specific enzymes catalyzing each reaction, with most enzyme names ending in "**ACE**".
* ⚡ Despite the overall cellular respiration process requiring oxygen, glycolysis does not, and instead generates a **net gain of two ATP molecules per glucose molecule**.
* 🔢 Glucose, a 6-carbon molecule, is broken down into two 3-carbon compounds (**pyruvate**) during glycolysis, with each step tracked for **carbon conservation**.
* 🔋 In addition to ATP production, glycolysis generates **NADH molecules**, which are crucial electron carriers for the later stages of cellular respiration.
* 💡 "So this is pyruvate at the end, and remember, it only shows **one pyruvate** because that's tracking from **one molecule of one 3-phosphoglycerate** when we know that we have **two of those from every molecule of glucose**."
* 🔄 The overall outcome of glycolysis for each glucose molecule is the production of **two pyruvate molecules**, a **net gain of two ATP**, and **two NADH molecules**.
* The electrons carried by NADH are derived from the breakdown of glucose bonds during glycolysis, setting the stage for their role in **subsequent cellular respiration processes**.

OK, so moving forward in our discussion of cellular respiration, we're going to talk in detail about the first process that's called glycolysis. And glycolysis occurs in the cytoplasm of the cell. So I want to make sure we understand that this is happening in eukaryotic cells and this is happening in prokaryotic cells. So the other thing that's important, even though the overall reaction of cellular respiration requires oxygen, this portion does not require oxygen. Now, let's get into the details. So we have multi-step reactions that are going on from glucose, and each of these. So when it has step number one, step number two, all of these, there is an enzyme that is catalyzing this reaction, a specific enzyme, and you'll notice that it has the enzyme name at the bottom. You don't need to know those enzyme things. But I do want to point out to you that most enzymes, their

name ends in ACE. And so I do want you to know that just like when we talked about metabolism or the overall chemical reactions in the cell, most of these are mediated or catalyzed by an individual enzyme. That's what lowers the energy of activation. So the reaction can go forward. OK, we start with glucose, and you'll see that we have a conversion to glucose six-phosphate. What's important is not for you to know those structures or to know the names of those, but to see that the cell is actually making an investment of ATP at this point. Remember, what's the overall goal of cellular respiration? Well, it's to produce ATP for the cell. So this seems counterintuitive that there's an investment of ATP, if that's actually what we're after, but in fact, still has to invest not one, but two molecules of ATP at the beginning of glycolysis. Now, what I want you to see is in step four, so so excuse me back at the beginning,

we need to make sure that we mark or note to ourselves that glucose has six carbons. So we're interested in following each one of these carbons all the way through until they become a carbon of carbon dioxide. So every carbon that we're beginning with in glucose, every one of these will eventually end up as a carbon in carbon dioxide. So we follow it through, we get to step forward and we see that these six carbons of glucose are now broken apart into three carbon compounds. We have two, three carbon compounds, but we still have our six carbons. If we count them up, we still have 6 carbons, we just now have two. It's been separated into two molecules rather than one. OK, and we move on continuing from there, and what I want you to see is here are these two carbon-containing compounds, right? There's three carbons here and there's three carbons here. We still have all six carbons. So this part here that says two times

that means each of these. So this is taking us one of these molecules all the way through till the end of glycolysis. Where we get a pyruvate. Two times means each of these molecules is going to have to go through this process. Right. So we do that times, too, because we're tracking an entire glucose molecule. So we see that overall at the end. For every glucose molecule, we're going to get two molecules of pyruvate. So this is pyruvate at the end, and remember, it only shows one pyruvate because that's tracking from one molecule of one three best bisphospho-glycerate when we know that we have two of those from every molecule of glucose. So do we still have all six carbons? Yes, we do, because pyruvate has three carbons, and we have two of those, so we haven't lost any carbons yet to carbon dioxide. The other thing I want you to see is we

have a production of ATP. So you can see that. The arrow here. What's coming in is ADP, and what we're getting out is ATP in both of these cases, whereas before we were investing ATP. So remember this. This happens twice for every one three bisphospho-glycerate. So if we do the math, we invested two ATP. So we were negative two ATP from the start. But we get two ATP out for every 1-3 bisphosphoglycerate, meaning four total for each glucose. So we're positive two ATP at the end of glycolysis. So in addition to two pyruvate, it's important that we see that we get it, we have a net gain of two ATP. And the other important thing that I want you to see is right here. We have the generation of a molecule that's an electron carrier called NADH, and remember this, it's happening two times. So that means we have two

NADH. Now, these are electron carriers, and these are going to be very important on our last stage when we talk about the electron transport chain. So we're going to keep track of how many of these NADH molecules we're generating as we go through this process. Now, one last thing I want to point out to you is where are the electrons coming from that are being carried by NADH? Well, we've seen that glucose has been broken down, so bonds have been broken, therefore releasing electrons. So these electrons that have been picked up by of these are from glucose.

Glycolysis: Glucose to Pyruvate

Natalie Russell

The Process of Glycolysis in Cellular Respiration

Glycolysis is the first step of cellular respiration, taking place in the cytoplasm of both eukaryotic and prokaryotic cells, and it does not require oxygen.

The multi-step process involves specific enzymes, with most of their names ending in ACE, and it includes an initial investment of two ATP molecules to ultimately produce ATP for the cell.

The Fate of Glucose Carbons in Glycolysis

Glucose's six carbons are ultimately transformed into two molecules of pyruvate during glycolysis.

Despite the carbon compounds being separated into two molecules, all six carbons from glucose are still present in the pyruvate.

This process shows that no carbons from the original glucose are lost as carbon dioxide during glycolysis.

ATP Production and Net Gain in Glycolysis

Glycolysis results in a net gain of two ATP for each glucose molecule.

In addition to ATP, it also generates the electron carrier molecule NADH.

The process involves investing two ATP initially, but ultimately leads to a positive two ATP at the end of glycolysis.

The Significance of NADH in the Electron Transport Chain

NADH is crucial for the electron transport chain, as it serves as an electron carrier generated during the process of glucose breakdown.

The electrons carried by NADH are derived from the breakdown of glucose bonds.

Keeping track of the production of NADH molecules is essential for the last stage of the electron transport chain.