Intro to Glycolysis: Study with Video Lessons, Practice Problems & Examples

Glycolysis is a crucial part of carbohydrate catabolism, occurring in the cytosol and consisting of two phases: the energy-consuming phase and the energy-producing phase. Initially, glucose (a 6-carbon molecule) is phosphorylated and cleaved into two Glyceraldehyde 3 Phosphate (G3P) molecules, consuming ATP. Subsequently, G3P is oxidized to produce pyruvate, generating NADH and ATP. This process can lead to either fermentation (anaerobic) or enter aerobic respiration, progressing to the Krebs Cycle and oxidative phosphorylation, ultimately yielding ATP.

Intro to Glycolysis Concept 1

Now in our journey to understand food catabolism, we can say that glycolysis is part of stage 2 of carbohydrate catabolism. And we're going to say that it oxidizes glucose to yield pyruvate and high energy molecules. In this case, we're talking about ATP and NADH. If we take a look here, remember we have stage 1, which is basically the breaking down of our proteins, carbohydrates, and lipids through digestion into their amino acids, monosaccharides, and fatty acids. Here, we're looking at the monosaccharides portion. We're going to say here that it takes place in the cytosol. This is the portion that is outside of the mitochondria and therefore does not require oxygen. If we take a look here, we have our monosaccharides, we've grayed out the amino acids and the fatty acids because we'll talk about those later on. For now, let's just focus on our monosaccharides. Here, they enter glycolysis, and in the process, we're going to create our high energy molecules in the form of NADH and ATP. NAD⁺ is what we have initially before it gains its electrons. Through glycolysis, we have our monosaccharide getting oxidized to create our pyruvate. We have 2 pyruvates that are being created. With this pyruvate, we've highlighted this portion, this Acetyl group portion, which is going to further go into Acetyl CoA formation. Now, this pyruvate that we create can either go through the fermentation route, which is under anaerobic respiration, the absence of oxygen, or it can go in the aerobic respiration route where it does need oxygen. And from there we go into stages 3 and 4, which take place within the mitochondrial matrix. Now remember, this is what we've learned so far in terms of food catabolism with stage 3 dealing with the Krebs cycle or the Citric Acid cycle. And then going into stage 4, which deals with the Electron Transport Chain (ETC) and oxidative phosphorylation and the formation of ATP molecules. Right? So just keep in mind, when we're talking about carbohydrate catabolism, we're taking a look at stage 2 and specifically glycolysis.

Intro to Glycolysis Example 1

Which one of the following molecules is not a product of glycolysis? Now remember, with glycolysis, we have our monosaccharides that go into it. And with it, we have NAD⁺ gaining electrons to become NADH. So, NADH is a product of glycolysis. In addition to this, we also have the formation of another high-energy molecule in the form of ATP. We also have the oxidation of our glucose which helps to form Pyruvate. So, Pyruvate is yet another thing that's created through glycolysis. What's not created is Acetyl CoA. Acetyl CoA happens later on in stage 3. But remember, glycolysis represents stage 2 of our carbohydrate catabolism. So here, answer d would be our answer. This is not a product of glycolysis.

Intro to Glycolysis Concept 2

In this video, we're going to take a look at the phases of glycolysis. Now, firstly, we're going to say that glycolysis is a linear catabolic pathway that consists of two phases. Now, here we're going to say Phase A is our energy-consuming phase. Here we have Phosphorylation and Bond Cleavage, a reaction that splits a glucose molecule. Remember, glucose molecules have six carbons. Now, here it's going to produce two molecules of Glyceraldehyde 3-Phosphate, which we will abbreviate as G3P. Because it's energy-consuming, it has to consume a high-energy molecule in the form of ATP. So here we have our glucose which is our six carbons. ATP is invested into this process; it's an energy-consuming one. Doing that helps us to split our glucose into two Glyceraldehyde 3-Phosphates.

Now, in the energy-producing phase, we're going to say that we have oxidation and dephosphorylation; it converts our Glyceraldehyde 3-Phosphate to Pyruvate. Remember, oxidation reactions here will produce NADH and ATP. So, this is the energy-producing phase of glycolysis. So here we have our two Glyceraldehyde 3-Phosphates. In the process of oxidation, we're going to create NADH, ATP, and as a result, our Glyceraldehyde 3-Phosphate is converted into two pyruvate molecules. Right? So just think of glycolysis broken down into these two simple phases at this point.

Intro to Glycolysis Example 2

Which of the following statements is incorrect about glycolysis? Glycolysis produces pyruvate, NADH, and ATP. Yes. This is true. These are our 3 major products of glycolysis. So, this is true. The first phase of glycolysis does not produce any energy. That is also true. Phase A is the energy-consuming phase of glycolysis. Phase B of glycolysis produces 2 molecules of Glyceraldehyde. Here this is false, this is incorrect because Phase B creates 2 molecules of Pyruvate by converting 2 molecules of Glyceraldehyde 3-phosphate. So this is what's incorrect. Now, here glycolysis produces more energy than it consumes. That is also true. Yes. It takes energy to go through phase A, but it's okay because the payout from phase B will be larger. You make more energy at the end than we've consumed in the beginning. So here, option D is correct. So here, the only statement that is incorrect would have to be choice C.

Which one of the following molecules is a source of energy in the energy-consuming phase of glycolysis?

• A. NADH
• B. FADH₂
• C. ATP
• D. Acetyl CoA

How many carbon atoms are lost when one glucose molecule undergoes glycolysis?

• A. 0
• B. 2
• C. 1
• D. 3

Here’s what students ask on this topic:

What is glycolysis and where does it occur in the cell?

Glycolysis is a metabolic pathway that breaks down glucose, a 6-carbon sugar, into two molecules of pyruvate, each containing 3 carbons. This process occurs in the cytosol of the cell, which is the fluid portion outside the mitochondria. Glycolysis does not require oxygen, making it an anaerobic process. It consists of two main phases: the energy-consuming phase, where ATP is used to phosphorylate glucose, and the energy-producing phase, where ATP and NADH are generated.

What are the two phases of glycolysis and what happens in each phase?

Glycolysis consists of two phases: the energy-consuming phase and the energy-producing phase. In the energy-consuming phase, glucose is phosphorylated and split into two molecules of Glyceraldehyde 3 Phosphate (G3P), consuming ATP in the process. In the energy-producing phase, G3P is oxidized to form pyruvate, generating ATP and NADH. Specifically, oxidation reactions convert G3P into pyruvate, producing high-energy molecules like ATP and NADH.

What are the end products of glycolysis?

The end products of glycolysis are two molecules of pyruvate, two molecules of ATP (net gain), and two molecules of NADH. Pyruvate can either enter the fermentation pathway under anaerobic conditions or proceed to the Krebs Cycle and oxidative phosphorylation under aerobic conditions, leading to further ATP production.

How is ATP generated during glycolysis?

ATP is generated during glycolysis through substrate-level phosphorylation. In the energy-consuming phase, ATP is used to phosphorylate glucose. In the energy-producing phase, the oxidation of Glyceraldehyde 3 Phosphate (G3P) leads to the production of ATP. Specifically, two molecules of ATP are produced for each molecule of G3P, resulting in a net gain of two ATP molecules per glucose molecule.

What role does NAD+ play in glycolysis?

NAD+ acts as an electron carrier in glycolysis. During the oxidation of Glyceraldehyde 3 Phosphate (G3P) to pyruvate, NAD+ is reduced to NADH by gaining electrons. This reduction is crucial for the continuation of glycolysis, as NADH carries the high-energy electrons to the electron transport chain in aerobic respiration or is reoxidized to NAD+ during fermentation in anaerobic conditions.