The Miracle of Ribosome Assembly Evolution

New research is uncovering the details of how the cell’s protein factory—the ribosome—is constructed. The ribosome translates messenger RNA molecules—edited copies of DNA protein-coding genes—into a string of amino acids, according to the genetic code. The ribosome has two major components (one smaller and one larger), each made up of both RNA and protein molecules, and is constructed via a complex sequence of events.

The RNA components of the ribosome are copies of DNA genes. These ribosomal RNA molecules—known as rRNAs—are initially in a raw copy of DNA which eventually is edited. For instance, one of these copies of DNA may contain many rRNAs, separated by spacer segments. The spacer segments need to be removed, leaving the individual rRNAs ready for assembly.

One of the findings of the new research is that in the early stages of assembly, one of the DNA copies folds up such that a spacer segment binds to one of the rRNAs. In particular, the spacer binds to the special segment of the rRNA that reads the messenger RNA molecules, in the final, assembled ribosome. When the spacer is removed, the rRNA switches to its correct shape, for function in the ribosome. One implication of this finding is that ribosome construction can be regulated by this switch. Remove the spacer and ribosome construction proceeds. Leave the spacer, and ribosome construction halts. As the researchers concluded:

our data show that the intrinsic ability of RNA to form stable structural switches is exploited to order and regulate RNA-dependent biological processes.

RNA tends to fold up into a variety of shapes. In this case, as lead researcher Katrin Karbstein suggests, RNA folding properties are part of the design:

Perhaps, nature has found a way to exploit RNA’s Achilles’ heel—its propensity to form alternative structures … Nature might be using this to stall important biological processes and allow for quality control and regulation.

But of course this mechanism brings yet more complexity:

What is interesting is that as the organism becomes more complex, the number of cleavages needed increases. This may make the process more accurate and that may be an evolutionary advantage, but even in bacteria this cutting is not done in a simple way. We still don’t know exactly why that is.

Karbstein suggests that the strictly ordered cutting and pasting steps in ribosome assembly are introduced to produce singularly perfect intermediates. As she explains:

Ribosomes make mistakes rarely, on the order of one in 10,000 amino acid changes. A lot of this accuracy depends on conversations between different parts of the ribosomes, so if the structure of the RNA isn’t correct, these conversations can’t happen. And that means more mistakes, and that’s not good because it can lead to any number of disease states.

Ribosomes don’t just happen. They are not easily assembled and the evolution of this choreography calls for several just-so heroics. Yes, this fine-tuned set of mechanisms makes for fantastic regulation of the cellular protein making factory, but it means that evolution must have gone through a stage where life didn’t work. For the spacer segment that binds to the rRNA is a show-stopper. It would be selected against instantly.

The only way to resolve this problem is to have the spacer removal mechanism already in place, before the spacer sequence itself evolved. As usual, evolutionists would need to rely on the needed mechanism just happening to serve some other useful purpose, and when the spacer sequence happened to arise for no reason, the removal mechanism found new work for itself. In other words, mutations arose that caused the DNA copy to fold, rendering ribosome synthesis—and life itself—impossible. But as luck would have it, there just happened to be the right molecular machine lying around that removed the problematic segment at just the right time and place. Not only was the fatal flaw obviated, but a brilliant new means of regulation invented. Amazing. Over time, further mutations happened to refine its actions and today we have the fine-tuned ribosome assembly process.

There you have it—evolution’s just-add-water version of science. For the umpteenth time evolution becomes a charade. Behind the scenes, in deep-time where no one can see it working, evolution once again performs miracle after miracle.