Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!utgpu!water!watmath!clyde!rutgers!ames!hao!boulder!pell From: pell@boulder.UUCP Newsgroups: sci.bio,sci.med,comp.ai,sci.misc Subject: Re: Taking AI models and applying them to biology... Message-ID: <1331@sigi.Colorado.EDU> Date: Tue, 9-Jun-87 22:49:55 EDT Article-I.D.: sigi.1331 Posted: Tue Jun 9 22:49:55 1987 Date-Received: Sat, 13-Jun-87 02:09:23 EDT References: <622@unicus.UUCP> Sender: news@sigi.Colorado.EDU Reply-To: pell@boulder.Colorado.EDU (Anthony Pelletier) Organization: University of Colorado, Boulder Lines: 68 Xref: utgpu sci.bio:351 sci.med:2060 comp.ai:465 sci.misc:274 (Craig D. Hubley) writes: (cognative psycology) >far from developing a bold new metaphor for human thinking, has (to a degree) >copied at least one metaphor from third-generation computer science. > one of the things that has always amused me is that, to the extent that I understand the structuring of computers, it seems that the cell and the computer scientists have come up with similar solutions to many of the same questions. This is particularly true when one looks at information flow in the cell. I feel comfortable in assuming that the cell had little help from the CS types in solving problems of information flow. It is likely to be true that contemporaries of in different scientific fields play with each other's ideas. This is why "Nature" insists on being so broad and why F.H.C.C. can get work. But I should stay more to the point. >The Question or WHAT DO YOU THINK? >---------------------------------- >Apparently, all human organ weights begin to decline shortly after puberty. >The cumulative effect of this seeming reduction of resources isn't felt so >strongly until middle-age, when we become more susceptible to disease. >- Is mitosis sufficiently prone to failure to account for organ decline? > >I've heard that mammal cells appear to suffer a "hard" reproductive limit >of 52 mitosis operations, and that meiosis "resets this counter" to 0. > It would seem to me that the step that is likely to give the cell trouble is not mitosis but DNA replication. If a whole chromosome lost or non-disjoined, that cell is in some serious trouble. Progressive accumulation mistakes through replication and general maintanence seems a more likely culprit. I confess that once the topic turns to outside the single cell or involves more than, say, two cells, I am hopelssly lost. So the question of aging is outside my capabilities. This will not, of course, stop me from volenteering the following: I have never liked the "hard-wired-number-of-mitosis" model. I am not sure why; it just seems implausible, or worse yet, unecessary. Supposedly "immortal" cells, like bacteria, actually have a rather high death rate in the population (try doing a particle count then plating them out to see how many are actually able to continue dividing). Their apparent immortality is the result of unrestrained growth. I suspect the failure rate is similar between bacteria and individual cells of a metazoan. The difference may be simply that a metazoan cannot tolerate unrestrained growth of cell populations. The cells are forced to stop dividing when in contact with other cells. they can be induced to re-enter the cycle by growth factors released, for example, when the skin is cut. I would guess that if one coupled the limitations on growth necessary to be a metazoan with accumulated errors, both during replication and simple maitanence, one could explain gradual breakdown of tissue without invoking the "hard-wire" model. oh well, I've gone on too long already. tony (few degrees are worth remembering--and none are worth predicting) Pelletier Molecular etc. Bio Boulder, Co. 80309-0347 P.S. I think alot about information flow problems and would enjoy discussions on that...if anyone wants to chat.