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.)
El Chupacabra?
--Boris
The article makes it already, no need for more. One can 'imagine' whatever one likes but to build such a system (which is only a small part of a greater system, which is intself only a small part of the greater system - the whole organism) takes a lot more than imagination.
Larry Niven calls them "The Handicapped". Dolphins. As I recall, in a few of his stories, humans aid them by providing prosthetic "hands"...
Whales evidently sing epic songs to one another; dolphins play. I dunno.
--Boris
Do you think horses haven't suffered predation from leopards, lions, tigers, cougars, wolf packs, and even humans? (Hint: the wild ancestors of the domestic horse typically weren't so impressively large. We bred them for that.)
You're sitting around thinking of reasons why things are impossible without magic. Everything's impossible if you're determeined to find it so, especially if you never stick your head out the door to check your work.
It's a long case, but there is one there to make. In general, the notion is that life is too complex to have naturally evolved. Not even over a billion years.
The terms that usually get used for this are like "Intelligent Design" or "Divine Design". There is a lot of stuff around. If you get into it, it's pretty interesting.
It is not necessarily Christian. The basic idea is just what I said above. Life as we know it could not have evolved.
Since you are so smart, suppose you tell us how the human eye with its numerous parts evolved gradually. Kindly include all the parts necessary for it to have proper functioning and also kindly do not use the words 'imagine', 'possibly', 'perhaps', 'maybe' or 'could be' which are not scientific terms.
No, we don't! Surely you didn't write that with a straight face.Progesterone is not a chemical that is waitng for something to do. If evolution as taught today is correct, we should have millions of currently useless chemicals in our body hanging around just in case evolution needs them. We don't.
It's chemistry, not morphology that is the bugaboo of Darwinism as it is currently taught.
Problem is that the above is not just due to a single mutation, it is a system. The makeup of the eye would be useless without the enzymes to clear it up. It all has to work together. In addition, need creates nothing at all without intelligence behind it.
Turtles have far better color vision than man. Why? I don't know. I can tell you how, but not why. The question of "why" begs the question of teleology, a doctrine explaining phenomena by their ends or purposes, and some evolutionists make the mistake of asking teleological questions. For their error the rest of us life scientists pay the price of having to defend the undefensible.
Until we find hard evidence of the creator and the blueprints, we will never know "why."
In the meantime, science muddles along trying to explain "how."
Yes indeed! Every creature could profit from more intelligence - some humans too!
Take a comparative endocrinology course and then tell me about it.
This is what gets really stretched. Lots of DNA similarities are non-functional and amount to viral infection scars, yet they trace a tree of common descent. There is no reason for a designer to be putting that stuff in there at all, much less for Him to be putting a pseudo-history in porpoises that makes it look like they're more related to camels than to sharks.
You inherit DNA changes whether they're good for you or not. Whether you live and/or pass your genes to anyone else is a function in part of how good your own heritage was. That, and luck. What we see in DNA makes sense against this model.
What kind of designer tries to pass forward forever every design change--even if it's just accidental noise--that isn't seriously harmful to the designed? What we see in DNA does not make sense against a designer model unless the designer is a mindless robot.
Instead of insulting people why don't you just show us all, oh genius, how the eye evolved and rid us of our ignorance?
It's not a matter of a bunch of uneducated, over-religious rubes being astounded by the complexity of biology, it's that the numbers just don't add up. That doesn't mean that there is nothing to evolution -- I believe that it does happen -- but it does mean that the currently taught dogma about a pimple on amoeba turning into an eye has to change. New theories to address reality are needed because the old ones aren't working.The emperor of evolution is buck naked. That doesn't mean that he can't find clothes somewhere else, but there are still too many of his followers who think that his current clothes look just fine.
But, the fact that we do not understand does not mean it didn't occur.
Then they switch to the mild intellectual putdown:
That the complexity of it all overwhelms you is not evidence that there is an "intelligent" designer.
And (often) they go into the anti-religion insult: “Oh, you just explain everything away with the Magic Man in the Sky.” – although they don’t seem to realize that a spiritual (super-natural) explanation that cannot be understood by Man is exactly the same as a “natural” explanation that cannot (yet) be understood by Man.
I give Rudder a lot of credit for making a calm, rational case for evolution without resorting to any sort of swipe at religion. That's unusual on these threads (I will note that VadeRetro has appeared and has made his obligatory comment about "magic").
You've stopped making sense. Read the posts again slowly.
I don't know, nor does anyone else. But still the search goes on.
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