Path: utzoo!attcan!uunet!lll-winken!lll-tis!ames!nrl-cmf!ukma!tut.cis.ohio-state.edu!bloom-beacon!athena.mit.edu!ayermish
From: ayermish@athena.mit.edu (Aimee Yermish)
Newsgroups: sci.bio
Subject: Re: Nature Articles. Anyone read them?
Keywords: amino acid tRNA charging code
Message-ID: <6209@bloom-beacon.MIT.EDU>
Date: 14 Jul 88 23:14:24 GMT
References: <1628@runx.ips.oz>
Sender: daemon@bloom-beacon.MIT.EDU
Reply-To: ayermish@athena.mit.edu (Aimee Yermish)
Organization: Massachusetts Institute of Technology
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Schimmel &co. found what appears to be the way transfer RNA molecules
know which amino acid to pick up.  They haven't done the whole code
yet, to my knowledge (lots of tedious work, if I'm not mistaken).

I had never before realized just how terrible science reporting is in
the popular press.  I heard and read several totally incomprehensible
articles about this discovery before I finally got sick of it and
found the real info myself.

"Second genetic code" is a nice term to latch on to.  The idea is that
the "first" genetic code tells you how to go from three bases in
messenger RNA to a particular transfer RNA.  The code that Schimmel's
working on tells you how to go from a particular transfer RNA to a
particular amino acid.  If you don't charge your tRNA with the right
amino acid, plugging it into the right spot in mRNA is worthless.

"Primitive" is, as far as I can tell, a poor choice of words.  The
media is making a big deal out of the fact that while mRNA uses
three-base codons, tRNA only uses two bases to specify an amino acid.
It's really very simple.  There are twenty amino acids used in
proteins (some are modified, later, but the argument still holds), and
you need a stop codon, too.  mRNA has only four possible bases
(adenine, cytosine, guanine, and uracil), so it must use three bases
in each codon to uniquely specify an amino acid (4x4=16, that's not
enough.  4x4x4=64, wayplenty).  In tRNA, there are one or two more
kinds of bases (pseudouracil is the only one I can think of offhand),
letting the cell uniquely specify an amino acid in only two bases
(sounds like Name that Tune, huh?).

"Performing some of the functions of DNA"  Wow, I hadn't even heard
that one before.  DNA has two functions.  It replicates itself and it
codes for proteins (and ribosomal and transfer RNA).  tRNA can't do
any of that, last I checked.  Maybe someone else could clarify?

--Aimee

------------------------------------------------------------------
Aimee Yermish		ayermish@athena.mit.edu
MIT couldn't care less about anything I say. 
(as long as I finish that last paper...)