Brent Meeker writes:

> Russell Standish wrote:
> > The NS article is
> > 
> >  issue 2556 of New Scientist magazine, 19 June 2006, page 50
> > 
> > the actual published work is
> > 
> > Cell, vol 122, p 133
> > 
> > What he measured was the age of carbon in DNA, which is only a tiny
> > fraction of the total number of atoms making up a cell. So I guess you
> > are right in your more restricted meaning of "same".
> > 
> > Cheers
> 
> I wonder what part of neuron remains over a long period time.  I can well 
> understand 
> the electrolytes and other components that are part of the metabolic cycle 
> turning 
> over fairly quickly.  But what about the structural protiens that give shape 
> to the 
> axons?  What about the myline sheath?  Do they really turn over quickly too?

All cellular components are continuously being repaired and replaced, including 
structural 
ones. I am not sure of the actual figures for individual components in human 
brains but 
probably protein turnover has a haf-life of days. For example, experiments with 
radiolabeled 
tyrosine suggest that half the protein in a mouse brain turns over every ten 
days:

http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1164796

Jesse Mazer quoted a study a while ago suggesting that turnover of synaptic 
structures 
was even more rapid, a matter of minutes, but I cannot find the reference.

Stathis Papaioannou
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