What do zebras and cholesterol have in common?

It’s not straightforward

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Animation by the author of Zebras, a Eukaryotic cell and a bacteria.

Earth is filled with magnificent creatures and a vast variety of ecosystems. From gigantic elephants to unimaginable tiny creatures.

In spite of their tremendous differences, they are all ruled by the same ruthless laws of nature. But, how do they work?

How does a cell know how much cholesterol has to be produced?

How is the number of zebras regulated?

Cellular cholesterol production

That’s right! Your body also produces cholesterol. So, in reality, you have two sources of cholesterol: food and your own cells might produce it.

But what exactly is cholesterol?

It’s a type of fat that, contrary to popular belief, is essential for you. In fact, you wouldn't be alive without it.

It’s so essential because it allows our cell membranes to be stable and the right amount of flexibility.

Animation by the author of how cholesterol influences cell membrane fluidity.


Cholesterol is produced following a so-called metabolic pathway. This is essentially a route of chemical reactions that your cells follow to transform an initial substance (acetyl-CoA) to a final product (cholesterol). Like this:

Animation by the author of the cholesterol metabolic pathway.

This is all sped up by enzymes. Enzymes are basically proteins that accelerate a chemical reaction. Think of them as tiny machines that make things go quicker in your cell.

For example, here, HMG-CoA becomes mevalonic acid. This process is accelerated by HMG-CoA reductase (an enzyme).

Animation by the author of HMG-CoA becoming Mevalonic Acid.

Although it has an intimidating name, HMG-CoA reductase is very important because it limits how much cholesterol can be produced.