Mitotic spindle and magnetic poles.
rsn_ at _comcast.net
Sat Nov 29 11:25:35 EST 2003
On 29 Nov 2003 01:50:55 -0800, rgregoryclark at yahoo.com (Robert Clark)
>r norman <rsn_ at _comcast.net> wrote in message news:<n678svknctqsnub9qerajfaie5ueprr783 at 4ax.com>...
>> 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.
>Take a look at the image of the mitotic spindle of a Drosophila embryo
>in Figs. 1,b and 1,c on this page:
>1. Study of the Effect of Electric Fields on E. coli
> Note that the spindles are straight close to the middle but are more
>rounded further out.
> Then compare this to the images of the field lines of magnetic and
>electric dipoles on the same page in Figs. 2 and 3. They are also
>straight close to the middle but more rounded further out.
> A definitive test would be to use the very sensitive magnetometers
>available now to see if the mitotic spindle generates a magnetic
>field. Inexpensive magnetometers are available now that can measure in
>the nanotesla range or 10 microgauss. As a comparison the magnetic
>field of the Earth is on the order of .5 gauss.
Yes, there is a resemblance of shape, but I still claim that this is
absolutely no indication of any resemblance of mechanism. That is,
there is no reason to believe that magnetic fields and forces are
involved in producing the shape of the mitotis spindle. The fact that
strong electromagnetic fields might disrupt the spindle does not
indicate that magnetic fields cause the spindle. The experiments
described in your web site are particularly strange since they have
absolutely nothing whatsoever to do with mitotic spindles!
The diagram shown as figure 1a in the web site described exactly what
I was saying about the spindle fibers. They tend to form in straight
lines, although they are flexible and can be bent by external forces.
What the diagram clearly shows are polar fibers the align antiparallel
where they meet. That forces the entire fiber, spanning from pole to
pole, to bend near the center. The entire shape is completely
explained by the tendency to form a straght line combined with the
tendency to align where the two meet. There is no reason to invoke
any other electric or magnetic force. The diagram also shows
kinetochore fibers, the ones that attach to the chromosomes, as being
pretty much completely straight, not bent. In reality, even the
astral fibers (the ones that just radiate out straight from the
spindle poles) are somewhat bent as they interact with other cell
structures and as they are deformed by the movements of both the
spindle poles and the chromosomes during mitosis.
More information about the Bioforum