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Usage of opsin
I'm trying to write about opsins, and I can't decide what the word should mean. The usage in the scientific literature is inconsistent. I can't find a pattern. It's giving me fits. The article will need a a usage section. J G Campbell (talk) 14:16, 11 March 2009 (UTC)
Retinal can be confused with retinal
- Not a good idea; it would be like making a disambig on neural, which can mean "of, or pertaining to, the neuron". Anyway, I just started the retinal article, feel free to contribute. --Sadi Carnot 14:53, 16 September 2006 (UTC)
"Light" Symbol in Figure
The symbol in your figure and caption looks like a "gamma" to me. In chemistry, "light" (UV to visible to IR) is frequently indicated by "h nu" (Planck's constant h, Greek nu). Or sometimes a squiggly thunderbolt symbol, if you have one. I'm not sure what gamma symbolizes except maybe gamma radiation. Gamma rays are used to induce some reactions, e.g., reactions in crystals.
- Whilst γ is used to represent gamma rays in the context of nuclear reactions, γ and hν may be used interchangeably to represent a photon of any energy. Eutactic (talk) 12:25, 18 February 2009 (UTC)
Conjugated instead of unsaturated
I’m not sure how to fit this theory in. See:
- Than, Ker (2007-04-10). "Early Earth Was Purple, Study Suggests". LiveScience.com. Retrieved 2007-04-16.
- Anitei, Stefan (2007-04-11). "Early Earth Was Purple!". Softpedia. Retrieved 2007-04-16.
- Rio S. (2007-04-11). "Purple was the old green... early Earth dominated by purple microbes". QJ.NET. Retrieved 2007-04-16.
—LOL 00:11, 16 April 2007 (UTC)
- The use of retinal by archaea is worth mentioning, if it isn't mentioned already. The Purple Earth hypothesis is far too far removed from the retinal molecule to be included in the same article. If a Purple Earth article is created (and I may if I get time) it would link here when mentioning retinal. Robert Brockway 07:23, 8 May 2007 (UTC)
In the overview section, "...the retinal molecule absorbs a photon into one of the pi bonds found between the eleventh and twelfth carbon atoms..." sounds bizarre. As far as I know, photons generally interact with an entire molecule and not with single bonds, even if the only change is seen in a single bond. Would it perhaps be more accurate to say something like "The incident photon induces a state change in a retinal molecule, causing the pi bond between carbons 11 and 12 to change conformation"? I don't think that really changes the accessibility of the article but avoids technical errors JaredAllred (talk) 17:34, 13 January 2008 (UTC)
Action potential generation
This article describes the vertebrate photocycle, which is fine, but then implies that photoreceptor cells generate "electrical impulses," which includes a link to the "electricity" page. This is very misleading. Vertebrate photoreceptors are NOT neurons, they are cells that release vesicles in response to graded changes in membrane potential. The photoreceptors synapse onto actual neurons, including retinal ganglion cells, which send action potentials (I think we should call them that, not vague "electrical impulses") through the optic nerve. In invertebrates (e.g. insects), the situation is different, but in that case the invertebrate photocycle should be described. 184.108.40.206 (talk) 22:43, 20 January 2008 (UTC)
- I agree it's misleading to suggest that photoreceptors generate propagating action potentials. But from most perspectives, photoreceptors ARE neurons. They develop from the same neural ectoderm as other retinal neurons. They have many of the same components as other neurons in their synaptic zone. "Cells that release vesicles in response to graded changes in membrane potential" describes any neuron. The difference I think you are trying to point out is that photoreceptors do not (normally) generate action potentials.
- Also, photoreceptors DO NOT synapse directly onto retinal ganglion cells. Photoreceptor signals reach RGCs through intervening bipolar and amacrine cells. --Chinasaur (talk) 14:41, 4 February 2009 (UTC)
Seems remiss not to include any mention of dehydroretinal, which in many vertebrate species (e.g. amphibians) is used as the chromophore instead of retinal for at least part of the animal's development. Not the greatest reference, but its a start... --Chinasaur (talk) 14:46, 4 February 2009 (UTC)
- I've put dehydroretinal in the chembox under related compounds. It's on my agenda. J G Campbell (talk) 22:38, 9 March 2009 (UTC)
Number of photons needed
I'm taking out this sentence: "It takes a minimum of five photons to trigger a nerve impulse", which cites Feynman's QED. This is wrong; you must have misinterpreted Feynman. See, for example:
S. Hecht, S. Shlaer, and M. H. Pirenne. Energy, quanta, and vision. The Journal of General Physiology, 25(6):819–840, 1942.
D. A. Baylor, T. D. Lamb, and K.-W. Yau. Responses of retinal rods to single photons. J Physiol, 288:613–634, March 1979.
H. B. Barlow, W. R. Levick, and M. Yoon. Responses to single quanta of light in retinal ganglion cells of the cat. Vision Res, Suppl 3:87–101, 1971.
- You're both right. Certainly, a single photon can photoisomerize the chromophore, and trigger a cascade; but about four of five photons entering the human eye under the best dark-adapted conditions go astray. The abstract of the cat reference supports this. Cats have tapeta lucida which make their eyes almost twice as efficient as human eyes in dim light. Almost two times almost three is about five. J G Campbell (talk) 17:04, 15 March 2009 (UTC)
GPCRs are sexy
"Heterotrimeric guanine nucleotide-binding protein (G protein)-coupled receptors (GPCRs) respond to a variety of different external stimuli ..."—Palczewski, et al. Kinky. J G Campbell (talk) 19:55, 14 March 2009 (UTC)