Fwd: [Plant-education] Glucose is no more a product
(by wise from uwosh.edu)
Wed Dec 19 11:32:09 EST 2007
>Forgive me for returning to an old theme that I have troubled you with in
>For half a century or more, it has been clear that the path of
>starch synthesis in chloroplasts starts with triose
>phosphates and progresses to polymer formation via
>glucose-1-P rather than free glucose. Glucose is no more a product of carbon
>assimilation by illuminated chloroplasts than is sucrose.
>So, why do textbooks insist that it is?.
>If you wish to read a recent article about this you can find it by pasting
>Best Christmas wishes
>>From David Alan Walker, FRS; Emeritus Professor of Photosynthesis,
>University of Sheffield, UK.
This has frustrated me too, and I have always
ascribed it to the fact that most biology
textbooks are written by non-plant biologists who
think that chloroplasts are merely green
mitochondria that perform reverse respiration.
With that mindset, and given that glycolysis
clearly starts with glucose, then photosynthesis
must produce glucose in order for the mythical
symmetry to be maintained.
Yes, it's both false and foolish.
Another chloroplast/mitochondrion myth that
drives me bonkers the the oft-repeated
(mis-)statement that mitochondria and
chloroplasts are both bounded by a double
membrane. That is only true if your sole source
of data is electron microscopy and all you are
looking at is STRUCTURE. Two lines around the
mito--two lines around the chloro--must be the
same. If however, you actually start asking
questions about the FUNCTION of those membranes
(and I certainly hope my students ask those sorts
of questions) then you have misled the reader.
Just ask yourself questions like, "where is
chemiosmosis taking place--which membrane? Lipid
synthesis? Carotenoid synthesis? Metabolite
transport?" and the analogous double membrane
myth quickly falls apart.
To quote me (from "The Structure and Function of Plastids" Springer)=
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