Mitotic spindle and magnetic poles.
rsn_ at _comcast.net
Tue Nov 25 22:36:08 EST 2003
On Tue, 25 Nov 2003 20:08:46 +0000, Tom Anderson
<ucgatan at socrates-a.ucl.ac.uk> wrote:
>On Tue, 25 Nov 2003, r norman wrote:
>> On 24 Nov 2003 22:06:58 -0800, rgregoryclark at yahoo.com (Robert Clark)
>> In the spindle, the process is very different. The spindle fibers
>> radiate outward from both poles. Some of these, the astral fibers,
>> always remain that way. These do not look at all like the magnetic or
>> electric dipole lines but look more like a magnetic or electric
>> monopole. Others meet (either by direct contact as in the polar
>> fibers or by connecting to the same chromosome in the kinetochore
>> fibers). These fibers tend to spread out from one pole and then
>> rejoin at the other, and so sort of look like the field lines of the
>> magnetic or electric dipole. Since the fibers that attach to the
>> chromosomes are the "important" ones, they are the ones shown in all
>> the diagrams.
>Ah, but if that was all it was, the spindle fibres would be straight,
>wouldn't they? They aren't, they definitely curved.
Are you sure they are curved? Don't look at diagrams or drawings.
Look at pictures of the fibers. Tubules tend to be straight except
that they are flexible and can bend around obstacles. The pictures of
the kinetochore tubules (the ones that attach to chromosomes) and the
astral tubules (the ones that radiate out) are distinctly straight
except when there are obvious obstacles bending them. The polar
tubule (the ones radiating from pole to pole without connecting to
chromosomes) are different. These are curved for a different reason.
Each one radiates out straight from the pole but, when they meet, they
tend to become aligned. These do have a curved shape somewhat
reminiscent of the field lines of a dipole (electric or magnetic) and
for the same reason that things that radiate out from one pole and
converge on another must necessary curve in between.
There is still no relationship to a magnetic dipole even though
intense magnetic fields may disrupt tubule formation.
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