P.S.

This week’s post is a postscript to the preceding one.

First, a correction. The (2) SLIDESHOWS (.pptx) and the STOP-MOTION ANIMATION (.mp4) made to go with the Gene Expression Simulation Bundle are available for free download on the Resources page. Enjoy!

Second, a little elaboration. I said that dsRNA (codon-anticodon pairing) is “the heart of the genetic code.” The poetic license used here should perhaps be suspended, or revoked. The word ‘heart’ was just used to indicate importance. Maybe a better metaphor for these short-lived, important little double-helices is a SECRET HANDSHAKE. Or rather, a set of 61 different secret handshakes.

What we should be sure to emphatically make clear is that each tRNA molecule acts as an ADAPTOR, physically coupling two things that otherwise would have no material connection. Or in linguistic terms (allegory again!), the tRNA is a “DECODER” - linking a byte from the GENE language (a specific mRNA codon) with a bit from the PROTEIN language (a specific amino acid).

{here’s a byte of binary code: 01101010 - this gets decoded as a ‘bit’ of our Roman alphabet, the lowercase letter j.}

OK, but now once these adaptors’ central role in gene expression is appreciated, you’ve got to ask: where do these come from?? Where’s the adaptor factory? Well, factories, plural actually - in fact 20 kinds, one for each kind of amino acid. Each of twenty different kinds of these enzymes (they’re all proteins) recognizes one or more (up to 6 at least) specific kind of tRNA, and loads it with just one specific kind of amino acid. (Mentioned on Slide 14 of the Gene Expression Pt.2 slideshow.) These enzymes have a regrettably unwieldy moniker, literally describing their biochemical activity: they are the AMINOACYL-tRNA SYNTHETASES.

With a name like that, it’s no wonder that they’re missing from the standards in a high school biology curriculum. But surely we must agree that they seem very, very important? Discuss.

Next blog post title: So What??