General Metabolism (Bio 101)

Metabolism? Common word — Not So Common Understanding

What really is this “metabolism” word that people always throw around?

Well, we should probably start from the beginning, shouldn’t we?

The Encyclopedia Britannica defines metabolism as “the sum of the chemical reactions that take place within each cell of a living organism and that provide energy for vital processes and for synthesizing new organic material.”[1]

There is one very important thing to realize about eating before we can get started:

==> The “form” that food comes into your body is not the way it stays in your body. You don’t eat fat, and then it just sits as fat in your stomach and liver. It breaks down into other compounds when it enters your body. Same thing with carbohydrate.

This known as “metabolism.” Generally speaking: metabolism is your body changing the molecular structure of compounds. This usually has to do with the morphing of food molecules into usable energy.

Metabolism exists as two main forms:

1)  The breaking down of a molecule is called “catabolism.” This is the kind of metabolism we are talking about when you are breaking down your food into “energy.”

2)  The building up of a molecule is called “anabolism.” This occurs when your body needs to produce nutrients and larger molecules (such as proteins for repair).

Your body heavily relies on both of these metabolic pathways. They both have to do with turning food into usable energy and other usable compounds.

Let’s look at a simple example on metabolism:

Metabolism of Carbohydrates

This might be throwing you way back to your freshman Biology class. Good!

It doesn’t ever hurt to do a quick refresher. “Quick” is maybe a strong word… But it is better to break it down slowly. There is no rush.

Once we break it down, we can build it back up with the juicy fats involved.

Cellular Respiration (Turning Carbs Into Energy)

The process outlined below can be found in any introductory Biology textbook.[2]

(It might seem “super sciency” sounding. Don’t worry about the other bio words! All you have to understand: the context in which we talk about metabolism, catabolism, and anabolism. We will be referring back to this list later on to help you understand.)

  • You eat a carbohydrate, such as bread.
  • Enzymes break down that carbohydrate into smaller pieces called “glucose.”
  • Your body breaks down that glucose sown into “pyruvate.”
  • That pyruvate then breaks down into “Acetyl-CoA.”
  • When that acetyl-CoA breaks down in the Krebs Cycle, “ADP” builds up into “ATP.” 
    • The energy released by breaking down a molecule is used in the building up of another.
  • From the Krebs Cycle, FAD and NAD+ receive electrons.
    • They build up into FADH2 and NADH — electron transporters.
  • These transporters “drop off” their electrons in the electron transport chain
    • The “dropping off” allows the creation of more ATP from ADP. 
    • Those electrons then end up reducing O2 into H2O.
  • This ATP is the energy of life
    • It holds tremendous amount of potential energy to be released for necessary functions across the whole body.
    • When it breaks up during other processes, that energy is released in one form or another.

Whew, that might have seemed like a lot. Quite a mouthful.

You might even be thinking to yourself, “Simple?!?! No way!” But again, the point was to understand that your body both breaks down molecules and builds them up.

(And there was a reason we chose the breaking down of glucose into energy. We will save that for later…)

Now, let’s move onto metabolism of fat – specifically saturated fat. This way we can fully understand what pathways it follows in our bodies. It is perfectly natural, and our body has quite the ability to use the fat we eat.

==> Metabolism of Saturated Fat


[1] “Metabolism”. Encyclopedia Britannica. (2018). [Online]. Available: Accessed: 13 May 2018.

[2] Campbell, NA, et al. (2017). Campbell Biology in Focus. Pearson Education Limited.

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