Tuesday, August 19, 2008

Topoisomerase



Every cell that has DNA needs a set of tools for copying it so the cell can reproduce. We turn over most cells in our bodies, so new ones have to be made. Also, when the organism reproduces, DNA must be replicated.


Last time I talked about Archaea and Cyanobacteria, since they are some of the first organisms to be seen in fossilized form on the Earth. We will see some of the microscopic tools these ancient organisms must have had from the start. To begin, they needed the DNA itself, shown at top. In my previous post I had a picture of the molecules which make up the rungs and sides of the DNA (which is shaped like a twisted ladder). Though scientists speculate that molecules evolved from RNA, these organisms all need DNA. Some of the DNA is stored in circular form, but it needs to be copied for reproduction and production of cell products, the proteins.


The molecule at the right in the top picture is called "topoisomerase." This molecule is necessary in the process of copying DNA. In circular DNA, it loosens the DNA which is packed tightly. A picture of a topoisomerase acting on a DNA strand is at left. The molecule in one species of Cyanobacteria has 933 amino acids, as shown in Uniprot Q2JJ84. The atoms of this molecule have to be arranged in an order that will do the job of systematically working on the DNA to prepare it for reproduction.

Each of the 933 amino acids themselves must be in correct order of atoms, since the order determines the arrangement of charges which hold the topoisomerase molecule together. The 933 amino acids first are connected in a straight line, but then they must attract each other in just a way to make folds that make a working machine.

The probability that 933 amino acids formed by chance 3.8 billion years ago so that the DNA of a Cyanobacteria could be copied is, as you might guess, infinitesimally small. It is less than 1 event in all the events of the universe so far, including chemical reactions (which is 10^150). But we have many more molecules to go to show the extent to which Cyanobacteria had probably already developed.

Many scientists think there was some way that these molecules could form naturally, such as following a law which caused arrangements that could perform these tasks. . The scientists insist life started without supernatural help from God. In the meantime, though they are far from finding the supposed way it happened, they are incensed when others are reluctant to believe a non-established theory that life somehow started by materialistic, naturalistic means.

Even many scientists who are Christian insist that it is unreasonable to look to direct supernatural intervention to explain life. Are they worried that children will not grow up with curiosity in science? I think curiosity is a human trait that comes from and through all circumstances. No one will stop wondering about science just because of Intelligent Design Theory. Some fear Intelligent Design Theory will suppress the pursuit of knowledge. I hope my blog shows that the more one pursues knowledge, the more the wonders of the biological world reveal earmarks of design.
Added 8/9/2010: I have moved from using the term "Intelligent Design Theory" to "Creationism" to describe my own stance. Though ID theory has done much to show the science of biology, the theological attitude is that the designer could be anyone. I do not agree with this. If you are a Christian, you believe that God is the creator and designer. Science cannot be separated from theology for a Christian in the way the ID advocates say.

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