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From: shenkin@cunixf.cc.columbia.edu (Peter S. Shenkin)
Newsgroups: sci.chem,sci.bio
Subject: Re: What is tortoise shell made of?
Message-ID: <1990Aug30.125414.19171@cunixf.cc.columbia.edu>
Date: 30 Aug 90 12:54:14 GMT
References: <1990Aug29.133624.8472@cunixf.cc.columbia.edu> <3984@kitty.UUCP>
Reply-To: shenkin@cunixf.cc.columbia.edu (Peter S. Shenkin)
Organization: Columbia University
Lines: 25

In article <3984@kitty.UUCP> larry@kitty.UUCP (Larry Lippman) writes:
>In article <1990Aug29.133624.8472@cunixf.cc.columbia.edu>, shenkin@cunixf.cc.columbia.edu (Peter S. Shenkin) writes:
>> Is it alpha chitin, or something else?
>
>	The exoskeleton of lobsters, snails and other crustaceans is formed
>of chitin (a polysaccharide and linear polymer of N-acetyl-d-glucosamine)
>impregnated with calcium carbonate.  It seems to me that the same material
>may constitute tortoise shells, but I do not know for certain...

I just asked a biologist, and got the following answer.  The shell is made
of something called dermal bone, a primitive sort of bone similar to our
skull bones.  The bone constituting the upper shell is bonded to the spine,
which is a unique architecture that I suppose defines tortoises/turtles.
However, the bone is covered with keretin, not chitin, as I had guessed,
and it is the keretin that we see, and which was used to make combs and
so on.  Keretin is proteinaceous, unlike chitin, which is a carbohydrate.

I suspect that, in general, vertebrates don't make chitin;  the exoskeletons,
of insects, as well as crustaceans, are made out of it.  

	-P.
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Peter S. Shenkin, Department of Chemistry, Barnard College, New York, NY  10027
(212)854-1418  shenkin@cunixc.cc.columbia.edu(Internet)  shenkin@cunixc(Bitnet)
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