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From: 6065833@pucc.UUCP
Newsgroups: sci.bio
Subject: Re: Human asymmetry
Message-ID: <2190@PUCC.PRINCETON.EDU>
Date: Sat, 4-Apr-87 16:02:45 EST
Article-I.D.: PUCC.2190
Posted: Sat Apr  4 16:02:45 1987
Date-Received: Sun, 5-Apr-87 14:12:44 EST
References: <1003@aecom.UUCP> <586@batcomputer.tn.cornell.edu>
Reply-To: 6065833@PUCC.PRINCETON.EDU
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Organization: Princeton University - Computing and Information Technology
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Disclaimer: Author bears full responsibility for contents of this article

In article <1003@aecom.UUCP>, werner@aecom.UUCP (Craig Werner) writes:
 
>Chemists cannot tell prochiral centers apart, but enzymes can.
 
Not true; they can deduce their chirality by looking at the structure
of derivatives of those molecules.
 
>        It turns out that the size of macromolecules ensures that they
>will always be assymetrical, and an assymetric molecule can react with
>a symmetrical one assymetrically.
 
The second part of this sentence is true, both by the rules of logic,
and common sense, but how does SIZE "ensure" anything?  The odds are
greater, when there are more asymmetrically bonding atoms involved,
that a macromolecule be asymmetrical, but there need not be asymmetry.
(And note the correct spelling of 'asymmetry,' please.)
 
>'Cilia are the roots of all handedness.'
 
Fine and well, but there is a deeper level still, which, since it isn't
fully understood, is perhaps overlooked in medical school, but is
addressed in some academic courses.  Namely, given that cilia give a
rotational orientation to a cell, how does the cell consistently
decide to differentiate along a specific axis?  There must be an internal
mechanism.  This may be in the cytoplasm (which is not a protein soup,
contrary to popular belief).
 
>        It turns out that this ciliary movement ensures that the heart will
>always be on the left side, and the liver on the right.
 
This is one hypothesis.  That the cilia are the deciding elements
is not proven, just strongly suggested.
 
>        Certain people are born without functional cilia.  In addition
>to being sterile, and have chronic respiratory disorders, half of them
>have their internal organs reversed (i.e., without cilia to give
>direction, rotation IS random).
 
If immotile cilia are the only possible cause of organ inversions, as
you seem to suggest, anyone with inverted organs must have defective
cilia, correct?  But I know someone who does not have Kartegner's Syndrome,
or anything else wrong with him, yet still has an inverted heart.
This suggests to me that the mechanism is not as simple as you suggest.
 
An aside:  this condition refers primarily to which side of the heart
the aorta, etc. are on.  In true inversion, everything is a mirror
image of a typical person's circulatory system.  Some people, however,
have their heart on the right side of their chest, but do not have
inversion.
 
>                              Craig Werner (MD/PhD '91)
 
Does '91 mean you are a First year or Second year med. student, Mr. Werner?
Personally, I prefer to avoid causing confusion by refering to myself as
a junior or senior or whatever.  After all, nothing is definite until it
is over.
Una Smith   6065833@PUCC
 
I thought signature files were silly until I realized I usually forget to
identify myself.  No longer.  Please forgive my apparent rudeness.