Posted on 09/08/2003 4:58:18 PM PDT by bondserv
How the Eye Lens Stays Clear 08/28/2003
To act as a true lens that can focus light, the lens of the eye must remain transparent for a lifetime. Yet the eye lens is not a piece of glass, but a growing, living tissue made up of cells. How can such a tissue stay clear, when the cells must be nourished, and when they contain organelles and chromosomes that would tend to obscure light?
Actually, that is exactly the problem with cataracts, one of the leading causes of blindness, in which the lens becomes clouded. Scientists at Bassnet Labs at Washington University (St. Louis, Missouri) have been studying how the eye maintains transparency, and found an enzyme that, when it fails, leads to cataracts in mice. The job of this enzyme is to chop up and dispose of DNA in lens cells. In a normal eye, “Light can pass through the lens because the cells break down their internal structures during development,” reports Science Now. Nagata et al. at the lab found large amounts of an enzyme named DLAD in mouse lens cells that chops up DNA for disposal. Mice lacking this enzyme developed cataracts. Failures in this enzyme, or the gene that codes for it, are also probably implicated in cataract development in humans.
Their work, published in Nature Aug. 28, explains how lens cells develop: “The eye lens is composed of fibre cells, which develop from the epithelial cells on the anterior surface of the lens. Differentiation into a lens fibre cell is accompanied by changes in cell shape, the expression of crystallins and the degradation of cellular organelles.” Until now it was not known how the cell dismantled its organelles and DNA. The fibre cells have their nuclei removed during maturation, but the DNA remains. It is the job of DLAD to act like a chipper and degrade the long DNA molecules into fragments that can be expelled. Even if the other aspects of fibre-cell cleanup succeed, this study shows that DNA stragglers are enough to cause cataracts.
So normal eye operation depends on the successful cleanup and removal of construction equipment and blueprints: organelles and DNA. Science Now tells a little more about these remarkable lens cells: “Even so, these cells aren’t simply empty; they house a highly organized network of proteins called crystallins* that transmit and focus the light passing through. Any disruption in this sophisticated scaffolding can cloud the lens, causing cataracts.” (Emphasis added.)
Here is an electron micrograph from Birkbeck College, UK showing how the fibre cells in the lens are stacked in neat rows like lumber with hexagonal edges for close packing.
What an amazing thing a living, transparent lens is. Did you ever think about this process, that a sophisticated molecular machine had to be produced from the DNA library that could chop up DNA into fragments, so that they could be removed and not obstruct the light path? Undoubtedly this is not the only enzyme involved in the cleanup job. Each fibre cell needs organelles and DNA during development, but they must be cleared away at the right time, and in the right order before the lens is deployed into operation, or else the user is denied the wonder of sight. This is just one tiny aspect of dozens of complex systems that all must work for vision to work.
Think of an eagle, detecting from high in the air a fish below the water, and using its visual sensors to accurately gauge its approach velocity, pitch, yaw and roll in order for it to capture food for the young in the nest, whose eyes are just opening to the world. Muscles, nerves, specialized tissues, detectors, software, image processing, cleanup, maintenance, lubrication and systems integration are just a few subsystems that must be accurately designed and coordinated in this, just one of many such complex sensory organs in the body.
Evolution is a fake fur that gives warm fuzzies to people who think in glittering generalities. Those who put on lab coats and examine the details and try to fit them into an evolutionary history get cold shudders.*A National Library of Medicine paper describes one of these crystallin proteins: “alpha-Crystallin is a major lens protein, comprising up to 40% of total lens proteins, where its structural function is to assist in maintaining the proper refractive index in the lens. In addition to its structural role, it has been shown to function in a chaperone-like manner. The chaperone-like function of alpha-crystallin will help prevent the formation of large light-scattering aggregates and possibly cataract. ... Reconstructed images of alpha B-crystallin obtained with cryo-electron microscopy support the concept that alpha B-crystallin is an extremely dynamic molecule and demonstrated that it has a hollow interior. Interestingly, we present evidence that native alpha-crystallin is significantly more thermally stable than either alpha A- or alpha B-crystallin alone. In fact, our experiments suggest that a 3:1 ratio of alpha A to alpha B subunit composition in an alpha-crystallin molecule is optimal in terms of thermal stability. This fascinating result explains the stoichiometric ratios of alpha A- and alpha B-crystallin subunits in the mammalian lens.” (Emphasis added.)
The fact that we do not understand or are able to explain it means that the gradual evolution of the eye is a matter of faith with you. It is not science. Therefore you have no call to insult those who do not believe as you do and call them names. In addition, that complex systems - and that includes the eye could have evolved is totally unreasonable and that is why there is not a single scientifically legitimate explanation by any evolutionist of the gradual development of any system or major organ of which there are dozens if not hundreds in human beings alone.
Yup, science does muddle along trying to explain how organisms work. However, evolutionists do not. For them, imagining is enough, they don't need no stinkin facts.
Then saying that those who do not believe it evolved should go take a biology course was a bit dishonest of you - don't ya think?
The problem with evolution is that it constantly says something is a fact when there is absolutely no scientific evidence for it. This is what you have done and what evolutionists do all the time.
I'm a chemist by training and not a bioligist and freely admit to knowing nothing about elasmobranchs. However, my point is not about chemicals like progesterone that have a purpose, but rather the chemicals that don't have a purpose. Evolution would predict that the body should be churning them out all the time but they're just not there.I've always found that chemists have a lot more doubt about the current theory of evolution than biologists. It sounds like a great idea at the big picture level but it runs into all sorts of problems at the molecular level.
Nova was showing cave divers in Florida. In the cave they were diving in, they discovered a layer of cloudy bacteria seperating different layers of water. The salt water was completely seperated from the fresh water, with the bacteria acting as a protective layer to prevent the layers from mixing.
Hmm, so much for their argument that a global flood would mix the waters, destroying either all the fresh water marine life or all of the salt water marine life.
More garbage from your bud Don Linsay who seems to write it to order. Send him five bucks he will write an article on anything you like.
Please, we are talking science here and that excludes Lindsay, TalkOrigins, Dawkins and Gould (and of course Darwin who asks us to 'imagine' that the eye evolved - some proof!) Well, if that's all that is needed then I ask you to imagine that it did not - now that is just a good a proof as yours!
If science went by the standards set by Darwin and the evolutionists, we would still be riding horses.
If all you can do is sneak the bar higher and say, "What's the EVIDENCE of that?" (or in gore terms, "What's the PROOF of that?") then you should drop the "there is no way" argument.
The lenses in your eyes are dead cells that filled with protein before migrating to their assigned spot and dying. The truth is more interesting than this made-up stuff.
You should take endocrinology--you'd love it. Actually many of our biochemicals are manufactured in stages, e.g, cholesterol to progesterone to 5-alpha dihydrotestosterone to testosterone, etc., etc. For some of these intermediary stages function has been found. For others it has not been elucidated. These are some intermediary stages in neurochemistry that are so short-lived that neuroscientists are sure they are not identifying them all. Then there are the neuoropeptides secreted by the hypothalamo-hypophyseal axis. One such has been isolated long ago (adrenalcorticotropic hormone) but still today even the best methods still produce a "contaminated" product that has other (unidentified) neuropeptides present. These contaminants are bioactive.
It is your limiting factor for allowing all of these fascinatingly, awesomely complex systems to simultaneously develop.
And that's not counting the time to come up with life in the first place.
Is that like a cemetary in a moving swamp? Or does the driver and the hearst just fizzle away? :-)
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.