Great question. We used to think that brain cells
stopped replicating soon after birth. It makes
sense because we learn when brain cells make
connections. New cells would be like late-comers
shoving their way into an intricate dance. It
turns out that there is some brain cell
replication in adults, though not a lot.
The mitochondria have basically the same DNA in
every cell. At least as far as we know. You
started out as one fertilized egg that got all its
mitochondria from your mom. The mitochondria have
their own DNA (that’s another story). Each time
the mitochondria divide, the DNA in them is
copied. There may be the occasional mutation, but
as far as we know, this is a random event. It’s
not controlled by whether the mitochondrion is in
a brain cell or a skin cell.
On the other hand, the DNA in the nucleus of
your brain cells and skin cells is also the same.
What is different is which parts of the DNA
are being used and how much they are being used.
As you say, mitochondria divide on their own
schedule. It must be regulated in some way or
cells that don’t divide much would end up packed
with mitochondria and fast dividers wouldn’t have
enough. It turns out that there are probably
several proteins that control mitochondria.
Mitochondria can fuse (squish together to make
one) as well as divide. This may allow them to
make repairs, change their shape and function, or
cause a cell to die (this is useful if the cell is
damaged or taken over by cancer or viruses).
It turns out that mitochondria are much more
interesting than the passive-looking ovals in your
textbook pictures. They’re travelling all
over the cell with the help of the cytoskeleton,
changing shape, breaking apart, getting together,
and probably doing other things we haven’t learned
If you were designing a way to trigger more
or less division of mitochondria, what would your
signal be? Oxygen level? Number of other
mitochondria around? Amount of ADP?
If you are interested in questions like this,
you might want to explore cell and molecular
Thanks for asking. I learned something today.