To: David Rice Nov2493 17:15:48 Subject: Denton's Follies, #3 DR On page 284 he produces a

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From: Martin Goldberg To: David Rice Nov-24-93 17:15:48 Subject: Denton's Follies, #3 DR> On page 284 he produces a list of protein sequence differences DR> between a lamprey and some other species. It reads (numbers DR> are percent): DR> DR> lamprey -- carp (fish) 75 DR> lamprey -- frog (amphibian) 81 DR> lamprey -- chicken (bird) 78 DR> lamprey -- kangaroo (marsupial) 76 DR> lamprey -- human (placental) 73 DR> I'll leave it to biologists to comment on other blunders found in DR> Denton. Similarity at the DNA and preotein levels is a good indicator of biological relatedness. But lets look a little closer as what is being studied... The "Wobble" hypothesis says that in each codon (triplette of DNA sequence) that codes for an amino acid, there is a certain amount of room for conservative replacements..that is that there are a number of different codons for the same amino acid. I don't have the genetic code here but I think that "CCC" codes for glycine. Now each codon for an amino acid always starts witht he same letter, ie. all glycine codons start with "C". But int he second and third positions, there is room for replacement or wobble. substituting some different bases int he second and third position will also produce a glycine in the chain. But what if it does not? It is well known that amino acids can have certain semi conservative replacements and still generate active proteins. This is nto always true but often it is. So, looking at a protein chain, it is not needed to have a large amount of sequence similarity in order for proteins to be functionally identical. Why is this? Because the areas that are of greatest importance are the so called active sites of proteins. These include the active sites that bind ligands, do enzymatic catalysis, and the like. Adn the normally accoutn for little of the proteins total amino acid content. Now don't get me wrong...the primary structure (sequence) of proteins is important as this contributes tot he tertiary (3-D conformation) of the protein. We cannot simnply walk away from it, but to claim that sequence similarity is the basis of all is not the entire answer. In my lab, I ma involved in a project that sprang from my isolation of a gene from a gene library of T. pallidum (syphilis) DNA. This gene produces a protein of a molecular weight of about 38k daltons. About 35% of it is similar to the MEGL-B protein of another bacterial organism. We are on the bverge of showing it perform the smae function....that is, the binding of maltose. Yet the protein in it's entirety is not that similar to that of the E. coli version. so much for the creationists claims that proteins have to be similar.


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