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Author
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Topic: a review
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ancient
Member
Member # 1649
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posted 13. May 2005 05:43
http://www.amazon.com/gp/product/customer-reviews/0684834936/ref=cm_cr_dp_2_1/102-5176147-2016962?%5Fencoding=UTF8&customer-reviews.sort%5Fby=-SubmissionDate&n=283155
quote:
A Biochemist Unimpressed with 'science' in the book, April 27, 2005
Reviewer: B. Kelch "BK"
I'll give a specific example. Behe used a calculation to try to show that a protein like trypsin (which is a protein in your intestines and helps you digest food) could never evolve through natural selection. Trypsin contains a specific kind of bond (called a disulfide bond) that stabilizes the structure of the protein; if this bond isn't formed then the protein doesn't work. Behe decided he'd try to predict the probability of a disulfide forming throughout natural selection. His calculation requires that the protein form a disulfide only at one certain position in the protein's structure, which was his first scientific error. A disulfide bond can form not just in one specific place in the protein for it to stabilize the protein, as Behe presumes in his calculation. Additionally, a protein doesn't necessarily need a disulfide bond to be stable, there are many other mechanisms to stabilize a protein than Behe considers in his calculations. When you factor these 2 caveats into the equations, then natural selection suddenly becomes much, much more attractive as a model for biological change than Behe claims.
any comments?
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David Carreon
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Member # 1837
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posted 14. December 2005 16:27
While it is true that disulfide bonds can form anywhere (between two cystines), it's not true that they'll have the same effect on the protein's final conformation if they are anywhere but where they're supposed to be. Displacing it one residue would likely cripple the protein (I'm sure people have done this: do a literature seach on the function of trypsin after various mutations and you'll get a bunch of papers).
While I haven't read the section referred to, I'm somewhat familiar with the argument. Even if you grant 10 other sites that the disulfide bond could go to make trypsin work exactly the same, it's only going to reduce the ridiculously impossible number to a slightly less ridiculously impossible one.
Also, there are other effects that lead to protein folding, disulfide bonds are by far (~10x) stronger than alternatives (such as ion-pairs or hydrogen bonds). So even if one assumes that it was possible to form a simliar bond with hydrogen bonding, it would require on the order of 18 additional amino acids to maintain the stability of one disulfide bond.
David
[ 14. December 2005, 16:30: Message edited by: David Carreon ]
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