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Catabolism: Definition & Examples

Instructor: Laura Foist

Laura has a Masters of Science in Food Science and Human Nutrition and has taught college Science.

In this lesson, we will learn about catabolic reactions and how they create energy for the body. Read on to learn more about catabolic reactions and why they're important to the body before testing your knowledge with a quiz.

What is Catabolism?

A hamburger may not only be delicious, but it will also give you energy to go about your day's activities. But how does that hamburger turn into energy? It happens through several reactions, all of which are catabolic. Catabolism is the breakdown of molecules into simpler ones. This process releases energy that can be used to fuel growth and activities, such as as running or jumping.

Let's return to that hamburger from earlier: It contains fat, protein, and carbohydrates. These are all basic sources of energy on which our bodies rely. The body can either immediately break them down for energy, or it can store them for later use: protein in the form of muscle, fat in the form of fat, and carbohydrates in the form of glycogen (a starch-like structure). For the body to use these substances for energy, they need to be broken down into smaller pieces through the process of catabolism. After being broken down into their simplest possible forms, energy can be released for use by the body.

The opposite of a catabolism is anabolism, the process of using simple molecules to create more complex units. This is how muscle, bone, and other parts of the body grow and are maintained. However, the two are intertelated, since catabolism must break down the molecules that anabolism then uses to create more complex units.

Catabolism Examples

The body has many catabolic reactions that take place to provide the body with usable energy. Lets look at the main ones that occur when you eat a hamburger in order to extract and utilize all of its energy: digestion, glycolysis, and beta oxidation.

Digestion

In order for us to eat the hamburger, we first chew it up. This is similar to the catabolic process. The teeth don't actually cause a reaction to occur, but a larger material is being broken down into smaller ones. Later in the process, enzymes in the saliva, stomach, and intestines actually break the larger molecules down into smaller ones:

  • Protein gets broken down into individual amino acids.
  • Carbohydrates get broken down into mono- or disaccharides, such as maltose or glucose.
  • Fat triglycerides get broken down into individual fatty acids.

Once the body has started the digestion process, these smaller units can be absorbed into the body. The energy from digestion cannot be stored by the body; the purpose of this step is simply to create small enough molecules for the body to absorb.

Glycolysis

The next step depends on the type of nutrient. Let's take glucose, the first source of energy that the body will utilize and the only source of energy that the brain can use. Glucose continues on into glycolysis. Through a series of reactions, glycolysis breaks the six-carbon glucose down into two three-carbon atoms called pyruvate. Since it is now a smaller molecule, energy (in the form of adenosine triphosphate, or ATP) can be released to be used by the body.

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