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Glycolysis Pathway: Steps, Products & Importance

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  • 0:05 Cellular Respiration
  • 0:50 Players and Stages of…
  • 3:24 Steps of Glycolysis
  • 5:32 Lesson Summary
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Lesson Transcript
Instructor: Kristin Klucevsek

Kristin has taught college Biology courses and has her doctorate in Biology.

Cellular respiration creates chemical energy in the form of ATP from the food we eat and the air we breathe. In this lesson, we'll learn about the first part of this process, glycolysis.

Cellular Respiration

When we're feeling tired or lethargic, sometimes all we need is some good food and some fresh air. A little outdoor picnic not only lifts our spirits, it also literally energizes us, as well as our cells. For a few lessons, we've done some dancing around cellular respiration, which is the process that converts food into chemical energy. All of our cells are constantly performing cellular respiration for us, and we can be reminded of this every time we sit down for a picnic and breathe in the open air. This air is chock full of oxygen. In this lesson and future lessons on cellular respiration, we'll walk through the steps that our cells take to use components in the food we consume and the air we breathe.

Players and Stages of Cellular Respiration

But first, let's step back for a reminder on the components of cellular respiration. The fancy chemical formula for cellular respiration is C6H12O6 + 6O2 + 32 ADP yields 6H2O + 6CO2 + 32 ATP.

C6H12O6, otherwise known as glucose, comes straight from the blueberry pie or whatever else is on your picnic plate. It represents the organic compounds that are derived from our food. O2, or oxygen, of course, is in the air that we breathe. You'll also remember that cellular respiration yields water and carbon dioxide. Carbon dioxide is removed from our bodies with every exhale.

Now, let's also take a second to review the final reactant in this equation, ADP, or adenosine diphosphate. An ADP molecule has two phosphate groups. You'll recall that this ADP is like an uncharged battery. The big goal of cellular respiration is to charge ADP to its fully energized form, otherwise known as the product ATP, or adenosine triphosphate. ATP is simply an ADP molecule with a third phosphate molecule.

Chemical structure of ADP and ATP
ATP Molecule

Take a good look at this chemical structure, because this is what cellular respiration is all about. ATP is the chemical energy that cellular respiration strives to make. It's essentially the chemical currency of life, used to 'pay' for all the reactions that cost energy in the cell. It's the energy that we get from our little picnic outdoors.

The last player in this chemical process we should remind ourselves of is not included in this equation. In our cells, we also have nicotinamide adenine dinucleotide, or NAD+, which is a coenzyme. NAD+ collects electrons and carries them to another location. When NAD+ picks up an electron, it becomes reduced and is now represented as NADH.

Now, creating ATP through cellular respiration is a long process. It occurs in three stages: glycolysis, the citric acid cycle, and the electron transport chain. In this lesson, we'll focus on what happens during glycolysis and how this feeds into the other stages. Glycolysis is the first stage in cellular respiration and happens in the cytoplasm.

Steps of Glycolysis

So to combine our players with the process, glycolysis is the first stage of cellular respiration and uses the following molecules: glucose, NAD+, ATP, and ADP. Glucose is a six-carbon sugar. We can represent glucose as a six-carbon sugar by using six blue circles, one blue circle for each carbon. In glycolysis, glucose is broken down using ten enzymatic reactions to produce two three-carbon molecules of pyruvate. Essentially, glucose is split in half and rearranged a bit.

Glucose is broken down to form two molecules of pyruvate
glucose split to form pyruvate

In this process, we come away with some valuable products. Instead of going through the nitty gritty of all the enzymes and chemical reactions involved, let's focus on some of the steps and how they get us to the next stage of cellular respiration. Importantly, we need to know that we use two ATP molecules to perform glycolysis. It may sound funny that we need to spend chemical energy to make chemical energy, but think of it like an investment of money that grows over time. You need to spend some chemical money to make some.

Glucose is transported into the cytoplasm of our cells. Here, it's rearranged and receives two phosphate groups from two different molecules of ATP, which then become ADP. Here, the addition of phosphate groups is represented by these two red circles. This is the energy investment.

Glucose receives two phosphate groups
phosphate group to glucose

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