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From: werner@aecom.UUCP (Craig Werner)
Newsgroups: sci.bio
Subject: Re: Analog/Digital Distinction
Message-ID: <590@aecom.UUCP>
Date: Thu, 13-Nov-86 00:16:05 EST
Article-I.D.: aecom.590
Posted: Thu Nov 13 00:16:05 1986
Date-Received: Sat, 15-Nov-86 23:58:37 EST
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Organization: Albert Einstein Coll. of Med., NY
Lines: 33
Summary: DNA Proofreading

> 
> 	The Genetic code is indeed 3-digit, base-4 numbers.  It's also an
> overloaded code 
	Not overloaded - it's redundant, which means sometimes mutations
can be silent at the level of the protein (and hence phenotype).
> 
> 	DNA exists in the cell most of the time as double stranded (dsDNA).
> 
> 	OK, now that we've got our base pairs, what do we do with them?
> Well, a wonderful thing happens -- an enzyme (Pol1?) comes along and
> re-reads both strands of the new dsDNA.  Every time it finds a place where
> a base-pair is wrong, it corrects it.  
>                                      how do you know which one to trust?
> The answer is that you don't!  You fix one of them at random and hope it's
> the right one.  


	First of all there is also another level of proofreading during
synthesis, so there is two chances to get it right before one leaves it
to chance. And of course, everyone I know is diploid.
	Secondly and totally irrelevantly, I would like to bring up a
quote attributed to someone who sequences genes for a living:

	"Since the DNA Polymerase, in-vivo and even in-vitro is much
better at proofreading than humans, the net result is that the mutation
rate of DNA sequences is much higher in press than in vivo."


-- 
			      Craig Werner (MD/PhD '91)
				!philabs!aecom!werner
              (1935-14E Eastchester Rd., Bronx NY 10461, 212-931-2517)
                                 "But I digress..."