I’ve been working hard this year to understand the secret world of amino acids. But amino acids are kind of useless all by themselves. It’s the way they join together that makes them so vitally important for life, or at least for life on Earth.
We’ve already looked at the anatomy of an amino acid. For today’s post, the crucial components are the amino group of one amino acid and the carboxyl group of another.
First, we remove one oxygen atom (the red ones) from the carboxyl group and two hydrogens (the white ones) from the amino group. One oxygen plus two hydrogens equals a water molecule: H2O.
Next, the carbon (in grey) in the carboxyl group reaches out for the nitrogen (in blue) in the amino group. When the two come together, they form what’s called a peptide bond.
This can happen over and over and over. One amino acids links up with another, which in turn links up with a third, which links with a forth and a fifth and a sixth….
I said at the beginning of this post that amino acids are kind of useless by themselves. That’s not quite fair. They can do plenty of fun, interesting chemistry on their own; but it’s this ability of theirs to form long peptide chains that makes them so useful (especially in a structural sense) for living organisms.
It’s entirely possible, in this big, wide universe of ours, that life exists without amino acids. But life without peptide bonds or something similar? Life without some easy way to string molecules together? Why, that would be pure science fiction!
P.S.: Or pure science fantasy, depending on how you define those terms.
Planet Pailly 
Life could be viewed as patterns of self replicating molecular strings run amok, at least as seen from the perspective of chemistry. Life is a molecular phenomenon, with macroscopic life just being immensely complex collections of that phenomenon. Looked at from that angle, it’s kind of amazing that it works as well as it does.
It also might show how arbitrary the distinction can be that we make between tribe/pack/groups of animals and the complex coalition of cells that is any one animal.
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Even single cells, as we currently think of them, are made of groups of organelles that work together. It may be that each organelle descends from what used to be a separate and distinct microorganism.
To this day, mitochondria still have their own DNA, separate from the DNA contained in the cell nucleus. So do chloroplasts, the organelles in plant cells responsible for photosynthesis.
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In ‘The Selfish Gene’, Richard Dawkins speculated that life began as self replicating molecules. Those gradually became more sophisticated, until they were something like what we now call DNA. Those molecules went on to develop mechanisms, carrying vehicles, to facilitate their replication. We call those mechanisms cells and organisms.
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I need to read more Dawkins.
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Dawkins is known as a strident atheist, but his science communications are mostly free of that. (Although be warned that he does let a little of it leak through.) I found ‘The Selfish Gene’ to be excellent. One of these days I hope to read ‘The Extended Phenotype.’
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