origin of light-sensitivity: C elegans cell senses light (The atheist delusion)

by David Turell , Tuesday, November 22, 2016, 00:59 (2922 days ago) @ David Turell

C. elegans is a very simple worm, in which a light-sensitive cell has been found:

http://www.livescience.com/56913-new-photoreceptor-found-in-worms.html

"An international team of researchers found the photoreceptor, called LITE-1, in the millimeter-long nematode Caenorhabditis elegans, a model animal that scientists often use in research. The finding is a remarkable one, they said, as it's only the third type of photoreceptor to be identified in animals. (The other two are opsins and cryptochromes, they said.)

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"An earlier study published by Xu and his colleagues showed that although nematodes have no eyes, they still move away from flashes of light. The new study suggests why: Instead of serving as an intermediary that senses chemicals formed by light reactions, LITE-1 absorbs light directly, "indicating that LITE-1 is highly efficient in capturing photons," they wrote in the study.

"'Photoreceptors convert light into a signal that the body can use," Xu said. "LITE-1 is unusual in that it is extremely efficient at absorbing both UV-A and UV-B light — 10 to 100 times greater than the two other types found in the animal kingdom: opsins and cryptochromes. The next step is to better understand why it has these amazing properties."

"After analyzing LITE-1's genetic code, the researchers realized that it was extremely different from photoreceptors found in plants, animals and microbes, Xu said.

Moreover, LITE-1 has several unique features. In animals, photoreceptors usually have two components: a base protein and a chromophore (a light-absorbing compound). If these two components are broken apart, the chromophore is still able to work, though not as well, the researchers said.

"In contrast, LITE-1 can't absorb light if its two components split up, Xu said.
In addition, the team found that LITE-1 is dependent on the amino acid tryptophan, which is present in two different places within it. To test this, researchers added a modified GUR-3, a nonlight-sensitive protein in the same family, to the tryptophan residues. However, GUR-3 only had about a third of the sensitivity to UV-B as LITE-1 did, they found."

Comment: Light sensitivity had to start somehow during evolution. It is hard to imagine C elegans stumbled upon this complex molecule by chance. Still it is a giant jump from this type of non-descript sensitivity to Cambrian animal eyes, which appeared with no precursors. No wonder Darwin was so afraid of the Cambrian Explosion and was sure stepwise forms would be found. They haven't been and the gap just gets wider and wider in their absence since the preceeding Ediacaran fossils have been well displayed with no eyes showing.