Let’s look more closely at the building blocks of DNA – the nucleotides.

Notice that it is more complex than an amino acid, where three complex chemical groups are covalently linked together. And unlike amino acids, nucleotides are not recovered in Miller-Urey type experiments. In fact, Robert Shapiro, professor emeritus of chemistry and senior research scientist at New York University, notes:

And no sample of a nucleotide, the building block of RNA or DNA, has ever been discovered in a natural source apart from Earth life. Or even take off the phosphate, one of the three parts, and no nucleoside has ever been put together. Nature has no inclination whatsoever to build nucleosides or nucleotides that we can detect, and the pharmaceutical industry has discovered this.

What is also remarkable about nucleotides is that it is possible to connect the sugar, phosphate group, and nitrogenous base together to form different structures.

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We’ve seen that the logic of protein structure entails the covalent linkage of a pattern of noncovalent interactions. This is how we encode a three-dimensional reality in one-dimensional terms. And all of this was made possible by the fact that amino acids are linked together in a way where their side chains were not involved in the linkage and thus served more like appendages.

But we have also seen this very logic is at play when it comes to the formation of a chain of nucleotides. As with the side chains of amino acids, the nitrogenous bases can interact with each other through noncovalent forces causing the nucleotide chain to fold into a three-dimensional structure. This is what happens with a lot of RNA and explains its ability to function as a catalyst. But let’s turn to DNA.

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We’ve seen that a protein is formed by covalently linking amino acids, yet in a fashion where the diverse side chains do not participate in this binding. This frees them to function elsewhere. So what do the side-chains do? In short, they interact with each other. Through electrostatic interactions, they fold most proteins into a compact, globular shape and it is the shape that is at the very heart of protein function (if you disrupt the shape, you disrupt the function).

What I’d like to do now is impress upon you the very brilliance of this design, as it goes a very long way in explaining why proteins have been so useful for evolution.

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