Tryptophan versus L-Tryptophan,
what’s the difference?

If you ever played with tinker toys as a kid,If you ever played with tinker toys as a kid,
You probably got A’s in Organic Chemistry.

Tinker toys and a lot of memorization, that’s about all it takes. Let me give you an example. Take amino acids. All the amino acids that you find in food - and that’s all we care about right now - follow a simple pattern. The atoms stick together in four easy-to-recognize groups, and these four groups form an amino acid. Here’s the basic pattern:

Ava's diagram of an amino acid.

The blue tinker toy is a nitrogen atom. Nitrogen is everywhere, so it’s nothing to be afraid of… except when it is used in explosives and fertilizers. In fact, almost 80% of the air we breathe is nitrogen, and the other 20%, give or take, is oxygen, depending on where you live.

Back in the time of the dinosaurs, in the Cretaceous era, when nuclear power plants were more tightly regulated, nitrogen was only about 68% and oxygen was a whopping 32% of the air, spawning the growth of giants of every sort: birds, fish, lizards, you name it.

Here's Ava teaching her first college course in organic chemistry.
from pine trees that hardens over time and traps small bubbles of air. These resin samples from the Cretaceous era were dated, and the air bubbles are changing our ideas of what made dinosaurs grow so big.

The red tinker toys are carbon atoms. There again, carbon is everywhere and nothing to be afraid of... except when it is used in thousands of different ways. And hydrogen (H) sticks to about everything, as you can see.


So, what’s the deal with “L” in front of the word L-Tryptophan? Tryptophan, like nearly all the other amino acids that link together to form proteins, can be assembled in two ways. Just like tinker toys.

You can stick the atoms together to make a lefthanded amino acid, hence we call it the “L” form. Actually, the L does not derive from the English word, left. It derives from the Greek prefix, levo, meaning “left”.

On the other hand… and even though such amino acids are absent from food… you can stick the same atoms together to make a right-handed amino acid. These amino acids are preceded by the letter “D”. In this case you would have D-Tryptophan. The D is derived from the Greek prefix, dextro, meaning “right”.

In nature, though, wherever you look, you find lefthanded amino acids, hence the “L” is so common it often is left off. People just leave it off because the L-form is about the only one you can find.

Last but not least, the amino acid, glycine, is the simplest amino acid, and where other amino acids have “other stuff” attached to that center carbon, glycine only has a hydrogen atom… so glycine is just too simple to create either a right or left handed molecule. That’s it!

If you have other questions for Ava, please let us know!

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