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Glycolysis: Phase One of Cellular Respiration

Glycolysis: Phase One of Cellular Respiration

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This lesson will describe in detail the processes that occur in the glycolysis phase of cellular respiration.

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Tutorial

Glycolysis

Source: Video and Images Created by Amanda Soderlind

Video Transcription

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Welcome to this lesson on glycolysis. Today, we will be describing the processes that occur in the glycolysis phase of cellular respiration.

Glycolysis this is the first step in cellular respiration. Cellular respiration is a process in which ATP, or adenosine triphosphate, is produced for the cell. ATP is basically an energy storage molecule that cells use.

In glycolysis, the main big thing that's occurring is that one glucose molecule is being transformed into two molecules of pyruvate. In just a moment, we're going to take a look at how that happens. Glycolysis occurs in the cytoplasm of the cell. And it does not require oxygen to happen, meaning it's an anaerobic process-- it does not require oxygen.

As I mentioned, the main thing that's happening is a glucose molecule is being transformed into two molecules of pyruvate. Let's take a look at how that's happening.

OK, so glucose is basically a six carbon sugar. I'm going to use these dots to represent the carbons. So we have a six carbon sugar, one, two, three, four, five, six. This is representing our glucose.

Glucose will enter the process of glycolysis. What's going to happen from there is that two ATPs will donate their phosphate groups to this glucose molecule. This is called phosphorylation. This donation of phosphate from ATP is called phosphorylation.

Basically, the purpose of this is to transfer energy. ATPs are transferring their energy to this glucose molecule, so that I can go through the following phases of glycolysis-- so that glycolysis can be carried out. ATP is donating one of its phosphates.

ATP stands for adenosine triphosphate. The prefix "tri" means three. So it has three phosphate groups attached to it. One ATP is donating a phosphate here, and another ATP is donating a phosphate here.

When an ATP gets rid of one of its phosphates, it becomes ADP, which means adenosine diphosphate, meaning it has two phosphates. This ATP molecule donated a phosphate and became ADP. And the same thing happened over here with another ATP.

The next thing that's going to happen is that this molecule is going to break down in half. Now we have two three-carbon molecules still with this phosphate group attached. Then the phosphates are going to be donated back to ATP.

After it donated its phosphate, it became ADP. And when it gains its phosphate back, it becomes ATP again. So then, we're left with two three-carbon molecules.

And each of these molecules is a molecule of pyruvate. You'll notice, we started with one molecule of glucose, and we ended up with two molecules of pyruvate. That's what's happening in glycolysis. Glucose is being broken down into pyruvate. Then pyruvate will move into the next phase of cellular respiration to produce more ATP.

This here is going to represent glycolysis. As I mentioned, glycolysis happens in the cytoplasm of the cell. You'll notice our later stages of cellular respiration occurred within the mitochondria. However, glycolysis occurs in the cytoplasm.

We have glucose that takes part in glycolysis-- so we have glucose entering the glycolysis phase. And in order for glycolysis to happen, ATP, two molecules of it, have to enter glycolysis. Remember, we mentioned that one ATP donated a phosphate here, and another ATP donated a phosphate here. So two molecules of ATP are being used in glycolysis, and two molecules of ATP are being produced.

Now, in actuality, four molecules of ATP are being produced. But since we used ATP for the process to occur, we only have a net gain of two ATP. So this is our net gain-- two ATPs from glycolysis.

And this ATP energy actually comes from previous cycles of cellular respiration. So we're using ATP that was made in previous cycles to power glycolysis, to produce more ATP here. So our net gain is two ATP out of glycolysis.

This lesson has been a brief overview on the processes that occur in the glycolysis phase of cellular respiration.

TERMS TO KNOW
  • Glycolysis

    The first stage of cellular respiration which breaks a molecule of glucose into two molecules of pyruvate.

  • Glucose

    A type of sugar used in glucose to produce ATP. Glucose is broken down in the first stage of cellular respiration.

  • ​Pyruvate

    A 3 carbon sugar produced when glucose is broken down in the glycolysis phase of cellular respiration.

  • Phopshorylation

    ​The transfer of a phosphate group from an ATP molecule  to another molecule thus the transfer of energy to that molecule.