Glycolysis and Cellular Respiration - Shmoop Introduction

What do playing video games, watching Dancing with the Stars, and doing your homework have in common? At first glance, not much. Two of these things are fun and one isn't. Don't worry; we won't judge you on which one is the most unpleasant for you. They do have something in common, though. They all require energy.

Most of us know that we need to eat food for energy—unless you're a plant, in which case you just soak up the sun and carbon dioxide. And if you are a plant, congrats on learning how to read.

How does food become useful to cells in the body? Cells can't process pizza, mac 'n' cheese, or Doritos in their natural state (note: we use the term "natural" loosely here). Instead, the body needs to break these foods down a bit. The process of converting food into useful energy at the cellular level is called cellular respiration.

Cellular respiration is a misleading name: usually "respiration" refers to breathing. In this case though, cellular respiration refers to converting glucose, a simple sugar (i.e., carbohydrate), into energy for cells.

Cellular respiration is a bit like an old-school arcade game. Head over to the change machine and exchange a dollar for some tokens. What we just did there, that's glycolysis—breaking a glucose molecule (dollar bill) into useable parts (tokens).

Now, it's time to play. First up, a rockin' pinball game called the citric acid cycle. Flashing lights and wicked pew-pew sounds, and we won two tickets and two bonus tokens. Our tickets are adenosine triphosphate (ATP) molecules, and we can spend these later on great prizes. And the bonus tokens work for the next game, oxidative phosphorylation.

Oxidative phosphorylation is where we're guaranteed to win the most tickets: 38 to be precise. With 38 ATP molecules, we can head over to the prize counter and use that energy to power all our daily activities. Sorry. We know you had your eye on that pink unicorn with the rainbow tail, but such is life.

So how exactly does ATP provide energy for the cell? ATP is a source of chemical energy that can be used to:

• Drive chemical reactions
• Transport substances across membranes
• Do mechanical work

Chemical energy is the energy released in a chemical reaction, like when certain chemical bonds are broken. One molecule of ATP has three phosphate groups that are bound together. When a bond between phosphates is broken, a lot of energy is released. This energy can be used to power other processes in the cell.