X-Message-Number: 2019
From:  (Phil Goetz)
Newsgroups: sci.cryonics
Subject: Re: Radiation
Message-ID: <>
Date: 23 Mar 93 22:37:09 GMT

References: <> 

In article <>  (Timothy Freeman) writes:
>To quote from "Freezing of living cells:  mechanisms and implications" by
>Peter Mazur:
>The dose of ionizing radiation that kills 63% of
>representative cultured mammalian cells at room temperature (1/e survival)
>is 200-400 rads (19).  Because terrestrial background radiation is some 0.1
>rad/yr, it ought to require some 2,000-4,000 yr at -196 degrees C to kill
>that fraction of a population of typical mammalian cells.

The dose that kills operating cells is only comparable to the dose that will
kill frozen cells if we assume that the cell's self-repairing mechanisms
come online immediately after reanimation.  That is, none of the enzymes
involved in DNA repair are damaged by freezing.

If DNA repair had to be "rebooted" by reproducing the repair enzymes from
the (damaged) DNA, it would take much less radiation to kill a cell.

A human chromosome has 6*10^9 purines in
each cell (genome length 3*10^9 base pairs, two copies of each chromosome).
The "average" human cell suffers 5,000 to 10,000 depurinations per cell per
day.  At an initial 7,500 depurinations/day, the number of undamaged
purines remaining would be halved about every 1100 years.  In 50 years,
you would expect one in every 44 purines to be damaged, which corresponds
to about one in every 44 amino acid products.  (1/2 of the time the
replication is done off the damaged strand; assuming damage to the third
codon position doesn't matter, each amino acid has 2 chances to be mutated,
so freq(amino acid mutation) = 1/2 * 2 * freq(b.p mutation).)
Try mutating one in every 44 amino acids of any protein; I guarantee the
protein won't work!

So you also have to ask what mechanism is causing those depurinations, and
how much it will be slowed down by freezing.  If a large percentage of them
are caused by radiation, the rate will not slow down much.


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