On Fri, May 16, 2014 at 11:02:35AM -0700, meekerdb wrote: > On 5/16/2014 12:55 AM, Bruno Marchal wrote: > >> > >>It turns out the carbon atoms in the DNA of neural cells is remarkable > >>long lived, as chronicled via the radiation spike due to atmospheric > >>nuclear weapons testing in 50s & 60s. I don't have a cite on hand, > >>but the result is that your neuronal DNA is on average about two years > >>younger than your own age. For most other cell types, the average age > >>is around 7 years, or something like that. > > > >That looks like the age of the cell, but all piece of DNA are > >changed many times, > > Do you mean replaced by a copy as part of cell metabolism (which I > think happens on cell division? Or do you mean each DNA molecule > suffers random changes during the life of a cell - due to radiation, > etc. > > >so the age of a DNA does not seem to me to be necessarily the age > >of the atoms making the structure. > > Of course the carbon atoms were produce in a super nova and are likely > millions of years old. >
What is being measured is the age of the DNA molecule, not that of the individual atoms. DNA is made up of carbon atoms, and the ratio of Carbon 14 to Carbon 12 will reflect the environmental ratio of those two isotopes at the time the DNA was constructed. In particular, during the period of atmospheric atomic testing, there was a spike in carbon 14, and this is visible in the DNA extracted from neurons of organisms born during that period, indicating that the DNA atoms haven't been replaced during the organism's lifetime. > >brain is the place where the metabolic activity is the highest, so > >I am not sure our neurons are so stable at the constitutive level. > > The common theory is that long term memories are encoded by growth > and change in neuronal axons and synaptic connections, which would > take metabolic activity. But it wouldn't require changes in neuron > cell DNA. > Yes - of more interest is whether or not the cytoskeleton's material structure is preserved, particularly in the axons, as this is presumably where memories are stored. I mainly offer this research tidbit as a counter to those who claim that every atom in our bodies has been replaced over the course of our lifetimes. Well, it just aint so. The situation is far more subtle. It's an open question as to whether the atoms that are preserved during a lifetime are important for an individual's identity, to be sure, but you can't just dismiss the question by saying that all atoms are recycled, hence identity cannot be tied to matter. -- ---------------------------------------------------------------------------- Prof Russell Standish Phone 0425 253119 (mobile) Principal, High Performance Coders Visiting Professor of Mathematics [email protected] University of New South Wales http://www.hpcoders.com.au Latest project: The Amoeba's Secret (http://www.hpcoders.com.au/AmoebasSecret.html) ---------------------------------------------------------------------------- -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
