Re: basic question about light

On Feb 9, 2:57 pm, "Androcles" <Engin...@xxxxxxxxxxxxxxxxxxxxxx>
wrote:
"Randy Poe" <poespam-t...@xxxxxxxxx> wrote in messagenews:1171023849.729057.285510@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Feb 8, 5:24 pm, "Androcles" <Engin...@xxxxxxxxxxxxxxxxxxxxxx>
wrote:
"Randy Poe" <poespam-t...@xxxxxxxxx> wrote in messagenews:1170952542.670726.97310@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
[A photon] is absorbed by a pigment molecule in your retina.

Are TV signals absorbed by aluminium molecules in the antenna?

Biological and man-made systems use different strategies. Visual
pigments are not conductors. Their electrons are bound to them,
not free as in an antenna.
Here's a partial description of the transduction process:
(fromhttp://webvision.med.utah.edu/photo1.html)

"Upon absorption of a photon of light, the retinal isomerizes from
the 11-cis form to an all-trans form which starts conformational
changes in the molecule resulting in bleaching. Several intermediaries
are formed in bleaching among them metarhodopsin II which activates
the G-protein transducin and a further cascade of events summarized
below (see review by Hargrave and McDowell (1992) and by Archer,
1995).
"Light transduces the visual pigment via the following enzyme
cascade:
photons - rhodopsin - activated rhodopsin (metarhodopsin II) - a GTP
binding protein (transducin) - an enzyme hydrolyzing cGMP
(cGMP-phosphodiesterase) - closes a membrane bound cGMP-gated
cation channel."

utah.edu, huh? The mormon home of cold fusion, wasn't it?

No, this is the med school.

Thanks for the word soup, I'm sure it would have been all very
interesting if I'd bothered to read it.

I know you have attention-span problems. I was hoping you
saw enough to point out that what I said was correct: a photon
is absorbed by a visual pigment, initiating a set of chemical
reactions.

Let me highlight the relevant part without straining your attention
span:

"Upon absorption of a photon of light, the retinal..."

Got that? The molecule absorbed a photon.

"... isomerizes from the 11-cis form to an all-trans form"

Got that? The effect was to change the shape of the
molecule. I won't strain you by going farther.

You don't like utah.edu. Fine, let's look elsewhere:
http://www.biologymad.com/NervousSystem/eyenotes.htm
"In the dark retinal is in the cis form, but when it absorbs a photon
of light it quickly switches to the trans form. This changes its
shape..."

Got that? "absorbs a photon"? "changes its shape"?

Want to see another?
http://www.math.utk.edu/~vasili/va/descr/phototrans/
Doesn't have a writeup. Instead refers to the Utah writeup as a
"spectacular link".

Another?
http://www.ch.ic.ac.uk/vchemlib/mim/bristol/retinal/retinal_text.htm
"When a photon of light falls onto rhodopsin, the molecule absorbs the
energy..."

Got that? The molecule absorbs the photon.

"...and the cis-double-bond between C-11 and C-12 in the retinal is
temporarily converted into a single bond. This means the molecule can
now
rotate around this bond, which it does by swivelling through 180°."

Sorry, too many big words for you. I lost you. That's OK, we'll just
skip
ahead a sentence or two to where it uses short words again

"... it changed the shape of the retinal from curved to straight.
Essentially,
the energy in a photon has been converted into atomic motion."

Got that? Changed the shape.

These chemical transducers are pretty cool, actually. It's too bad
you don't believe in them.

I hope you'll agree that "isomerizing resulting in bleaching" or "an
enzyme cascade" is not a description of anything that happens in
an aluminum antenna upon absorption of a photon. It is, however,
what happens in your eye.

I hope you'll agree that antennae come in different sizes, with
giraffementhttp://www.mccullagh.org/db9/10d-17/giraffe-1.jpg

Yes they do, but visual pigments (sorry, you don't understand that)
I mean visual MOLECULES are not antennas.

to shrewment
http://www.taiga.net/wmac/consandmanagementplan_volume3/graphics/phot...

molecules with pigment
http://www.snoopy.com/comics/peanuts/meet_the_gang/images/meet_pig_pe...

Do you not know what "pigment" means?

molecules
somewhere in the middle to do the photon absorbing, but you
didn't answer my question, Blind Poe. Please note the word
"basic" in the thread title.

Which part of :
"Are
TV
signals
absorbed
by
aluminium
molecules
in
the
antenna?"
did you not understand?

I always have to slow things down for you, don't I?

The answer is: No. TV signals are not absorbed by Al
molecules in an antenna.

The followup is: That has nothing to do with the question
of how visual pigments work, since visual pigments are
not aluminum antennas.

Does that help?

- Randy

.

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