Miracles of Science 3 RNA World Part 2

And, and the first thing I want to talk about is processing of RNAs.

Basic concept, almost all RNAs begin as an immature pre-RNA.

Pre-RNAs tend to be longer than the mature RNA because they contain a lot of information that tells the cell what to do with that RNA.

After all, the RNA is transcribed in the nucleus there off the DNA, but it does its work somewhere else in the cell.

So there's information in that immature RNA that tells the cell where to deliver this RNA.

It tells the cell what molecular machines this RNA may be participating in and, and gets it there.

And it provides all the inform-- in the RNA, all the information necessary to, to mature the RNA and get it ready to go to work.

So if someone talks about a tRNA, let's say, you should automatically assume that there must be a pre-tRNA family.

So just like you're used to thinking about pre-messenger RNAs, which are longer, have a lot more information than the actual molecule that, that makes a protein, there are pre-RNAs for every other kind of RNA as well.

And the other thing that's important to remember is all that information, none of it's wasted.

All of that information is necessary for the RNA to do its job, but it's usually gotten rid of before the RNA goes to work to do its job.

And so most of the time, processing an RNA means trimming things out as their use is finished, so you can get the RNA which is smaller then to be ready to go to work.

RNAs are processed, and they're processed because you need information to tell the cell what to do with the RNA before it can go to work, and you don't want that stuff in the way when the RNA gets ready to go to work.

Make sense? I hope so.

So it gets a little more [chuckles] complex than that because sometimes, I should say many times, in addition to getting rid of maybe thousands of nucleotides, a, a step in the processing is to add a few more nucleotides.

And so the general principle that pre-RNAs are longer than mature RNAs is, is certainly essentially always true.

But during that process, you may add some nucleotides to do something that, that has to happen a little later.

Now, a good example of that is the a- addition of stretch of the nucleotide adenosine.

Remember, there are four nucleotides, A, C, G, U in RNA, and so adenosine is one of the nucleotides that's present in RNA.

It's part of the genetic code.

But after a pre-mRNA is fully transcribed or while it's being transcribed, almost always there's an addition of a run of a bunch of As, A-A-A-A-A-A.

And that addition happens at the end, the three-prime end of a pre-mRNA.

Remember, RNAs are read left to right, just like you read in a book.

The left end of the RNA is called a five-prime end, and the right end is the three-prime end, and that has to do with the chemistry of nucleotides.

Doesn't really matter.