Molecular Monday: Meet Glycine

Friends, I’ve told you before: chemistry is hard. But I think I’ve learned enough to be able to introduce you to our first amino acid. This is glycine, the simplest amino acid.

By my count, amino acids have four key components. They are (in no particular order):

• An amino group: the part that gives amino acids their name.
• A carboxyl group: the part that includes a loosely attached hydrogen atom, which makes an amino acid an acid.
• An alpha carbon: provides structural stability by separating the amino and carboxyl groups. In the highly technical diagram above, the atom with the smiley face is the alpha carbon.
• The side chain: a group of atoms that attaches to one of the alpha carbon’s two extra bonding sites. An additional hydrogen atom caps whichever bonding site isn’t used for the side chain.

It’s these side chains which really distinguish one amino acid from another. Depending on which side the side chain attaches to, we’ll either have a right-handed or left-handed amino acid.

It’s important to be aware of the “handedness” of amino acids (of the “chirality” of amino acids, to use the technical term). Human DNA and the DNA of all life on Earth only codes for left-handed amino acids. In theory, there could be life forms on other planets that rely on the right-handed kind.

But glycine is a special case. Glycine’s side chain, if we can justifiably call it a side chain, is one single hydrogen atom. This is why glycine is considered the simplest amino acid: you can’t get much simpler than one hydrogen.

Also, this single hydrogen “chain” is indistinguishable from the single hydrogen used to cap the alpha carbon’s other free bonding site. This means glycine is non-chiral. It can be either right-handed or left-handed. I supposed you could say glycine is ambidextrous.

Because glycine is non-chiral and because it is the simplest amino acid, I have a feeling glycine could play a special role in astrobiology. Maybe… just maybe… glycine is universal to all life in the cosmos.

Or maybe not. This is just a pet theory I came up with based on what I’ve learned so far.  I’m sure I’ll have more to say about this as we get to know some of the other amino acids.

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Today’s post is part of a special series here on Planet Pailly called Molecular Mondays. Every other Monday, I struggle valiantly to understand and explain some concept in the field of chemistry. Please note: I suck at chemistry, but I’m trying to learn. If I made a mistake, please, please, please let me know so I can get better.