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.)
While you may call the above an 'unfair' question, it is not. It is what science is about - what is the evidence for something. Therefore, right there you are admitting that you are not talking science at all.
Now, if all it takes for something to be true is imagining it, well, not only can I imagine a flying pig, but I can even give you a gif of it!:
Au Contraire! Such terms are not out of place in scientific discourse. Scientists are continually seeking to improve their knowledge and understanding of all that surrounds us ("Creation", if you please...). We scientists know that our data, knowledge and understanding are incomplete; hence we must, in all honesty, use terms like "approximate", "perhaps", "possibly", "maybe", :could be", et cetera.
It is only those who think/believe they "know" -- in a doctrinaire sense -- that they have the only "true" answer... who have the ignorant effrontery to make supercilious statements like yours quoted above.
FWIW, and before you label me in your mind as a "heathen", know this: I am a born-again believer in Christ Jesus, and accept the bare outline of creation in Genesis as fundamental truth. (The Bible, is, after all, a spiritual guide -- not a science text.)
However, as a scientist (physical chemist), I consider it my calling in life to "read" the "other book" God left as a record for us -- all his mighty works -- so that I might seek to understand the majesty of all that He has made. Where you sneeringly use the term, "evolved", I prefer, "how He did it".
Supercilious, sneering remarks like yours only serve to diminish you (and your witness) in the eyes of those you might seek to reach for Christ. Childish taunting of intelligent people who have spent their lives seeking knowledge only weakens your case.
"As man extends the radius of his knowledge, the circumference on which he confronts his ignorance increases by a factor of 2 Pi..."
At least we scientists are honest enough to acknowledge our ignorance...
I agree with boris concerning the overall enigma of eyeness in evolution theory!
Y'all might find the following article - from the evolution side - frank and refreshing:
Giving a long list of true facts does not prove evolution. The problem is that there are many essential processes in life which are quite complex and which do not work at all without numerous different parts working together. This is an impossibility for gradual evolution since the different parts would be useless until all the parts were present - and working together as a unit. More important, the numerous systems in an organism all have to be present and work together also. Can you live without a heart, without lungs, without a brain, a stomach? There you have the problem for evolution - systems within systems within systems - all having to work together and be present for life to be possible.
What is your evidence that this is true? The limited humans understanding at this time might not explain every single facet, but that doesn't rule it out or prove that it's impossible.
Imagination is a creative, intelligent, designing process.
Have I threatened you?
Pretty good point.
In a spiritual sense, all of us should "evolve a brain" so we can see.
I'm not arguing that imagination is undirected or unintelligent. Your reply misses my point.
If you say something needs God, angels, or aliens to happen, I shouldn't be able to imagine a scenario in which it happens without same.
"here would seem to be a niche for long-winded predators with legs as long as horses."
I guess this is the obverse of the "panda's thumb," which I never found convincing (nature's specimens are not "perfect," therefore all life forms developed at the juncture of random mutation and natural selection).
You can imagine pigs flying all you like. That is not science though, it is not reality either. You can live in a world made up of your own fictions if you like, but most of us would rather live and function in the real world.
You rejected that exact same criticism when I pointed it out about one of your articles purporting to "disprove" evolution.
And people say you don't remember things - nice to see that my posts get recycled ;)
I don't know, but octopuses and mammals independently arrived at the same sort of plan for eyeballs. Furthermore, jellyfish and neon tetra fish both show that transparent tissues can certainly come into being, especially when it means they won't get eaten.
And why not an eye in the back of my head? Wouldn't that be handy?
Maybe it would - spiders have about a dozen eyes and flies, hundreds or thousands. Prey birds have only two eyes, but their visual fields span nearly the entire view, front to back. But predatory birds, like owls, have eyes on the front of their heads, just like we go. Is this evidence of a designer, or evidence that prey animals which can't see behind them are eaten (and don't reproduce), while predators that don't have good stereoscopic vision can't catch prey (and don't reproduce)?
However, as one who has degrees in chemistry and chemical engineering (and a whole lot of math since school), the odds for all these amazing things happening in the same place -- like the eyeball -- seem pretty slim, no matter how much time you give it.
The odds change significantly if the survival of a species depends on it. Consider the odds of a bacterium resisting any given antibiotic. And then multiply these odds by each other to come up with astronomically unlikely odds that no bacterium can possibly resist a few or even a dozen different types of antibiotics.
And then wonder why it is that there exist so many multiply-resistant bacteria, especially in hospitals. Additionally, consider that you can grow a petri dish-full of these bugs with a non-resistant strain, some mutagen, and all the antibiotics you wish to develop a resistance against. Simply dose the dish with a near-but-not-quite-fatal dose of antibiotic #1, and some mutagen, until you have a strain that resists #1. Then repeat with antibiotic #s 2, 3, and 4. (Etc.) At the end of the process, which might only take a week or month, you have not just one, but billions of bacteria that are resistant to every single drug you have exposed them too. Tell me, what are the odds against that? Replace the mutagen with billions of years, and the antibiotics with all the other critters out there that are trying to eat them, and you can get pretty crazy survival strategies, like locusts that emerge only every 17 years, or stick bugs that look just like little twigs.
Darwinism seems nice and neat and tidy from a macro standpoint, like when looking at the similarities between a shark and a tuna, but when you get down to the level of chemical compounds, evolution all of a sudden becomes immensely more complicated than was dreamed of even a few years ago.
On the contrary, my example of how to develop antibiotic resistance is very much understood at the molecular level.
To come up with something as complicated as the eye, our bodies ought to be full of millions of different chemicals just hanging around for evolution to perhaps find them useful. However, our bodies just aren't that way and we seem to have exactly the chemicals we need -- no more, no less -- in exactly the right places.
Not so - there are unexpressed proteins in all of us, that some diseases are simply the unwanted expressions of. Why do we have appendicies? Why do hens have the genes for teeth, or snakes the genes for arms and legs? They're in there, they're just not in use right now. But if non-teethed hens or legless snakes were put under survival pressure, some mutants that did have teeth, or legs, would find a greater chance to reproduce, and we would again see birds with teeth, and lizards, that toothless birds and snakes once descended from.
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