Welcome to Molecular Monday! On the first Monday of the month, we take a closer look at the atoms and molecules that make up our physical universe. Today, we’re looking at:
AMINO ACIDS ON TITAN
My spaceship has completed orbital insertion at Saturn. During last year’s Mission to the Solar System, I missed the opportunity to explore Saturn’s largest moon, Titan, in any detail. I intend to correct that error.
Titan may or may not support life, but one thing is certain: it is a chemically active world. And that chemical activity is vaguely reminiscent to the biochemistry found on Earth.
While my spaceship is still on approach to Titan, this seems like a good time to review what I’ve learned so far about amino acids.
Anatomy of an Amino Acid
- Amino Group: a structure on one side of an amino acid that can serve as a base in acid/base chemistry.
- Carboxyl Group: a structure on the opposite side of the amino acid that can serve as an acid for acid/base chemistry.
- Alpha Carbon: A single carbon atom separating the amino and carboxyl groups, preventing them from accidentally reacting with each other. Some amino acids also include a beta carbon, a gamma carbon, or even a delta carbon, further separating the amino and carboxyl groups.
- The Side Chain: A chain of atoms dangling from the alpha carbon. These side chains vary in composition and complexity, giving each amino acid its own unique flavor (sometimes literally).
Functionality of Amino Acids
- Peptide Bonds: The amino group of one amino acid can link up with the carboxyl group of another, forming a peptide bond (a water molecule is produced as a byproduct). This process can be repeated over and over, forming incredibly long peptide chains.
- Proteinogenic Amino Acids: While there are hundreds (perhaps thousands) of different amino acids, life on Earth uses only twenty-three of them in the formation of proteins. We humans use only twenty-one.
- Chirality: Side chains can be attached to one side of an alpha carbon or the other. Life on Earth only uses amino acids with side chains on the “left” side. Right-sided side chains are incompatible with our DNA, and we can’t use them for the construction of proteins (though our bodies can use some of them for other purposes).
When I arrive on the surface of Titan, I do not know what I will find. Amino acids? Probably. Peptide bonding? Maybe. Long peptide chains, like some sort of proto-DNA? It’s possible.
We’ll just have to wait and see what happens when I get there.