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"Our cells repair DNA copying errors"

Juustin

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Juustin
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Dec 19, 2006
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Partially because of the note in this weeks SWIFT bulletin, and partially because I sometimes do these things to try to stimulate my brain, I just paid a visit to the Official Jehovah's Witness website, watchtower.org, to check out the newer articles. I enjoy reading the more "scientific" articles, because they often employ a lot of logical fallacies and it's fun to try and spot them.

Anyway, I found this in their current article about aging:

The fact that we do not wear out was seen to be even more remarkable when biologists began studying the molecules within living cells. When your cells are regenerated, each new cell must have a copy of your DNA, the molecule that contains much of the information needed to reproduce your entire body. Imagine how many times DNA has been reproduced, not just during your lifetime in your own body but since human life began! To understand how amazing this is, consider what would happen if you used a photocopier to copy a document and then used the new copy to make the next copy. If you did this repeatedly, the quality of the copies would deteriorate and eventually become unreadable. Happily, the quality of our DNA does not deteriorate or wear out when our cells repeatedly divide. Why? Because our cells have many ways of repairing DNA copy errors. If that were not true, mankind would long ago have become a pile of dust!
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My question is this: Obviously if DNA was able to be "corrected" everytime there was a copying error, it seems like a lot of problems would be cleared up in the world. I just wanted to check in with anyone with more of a genetic/biology background than myself, and see if this statement is completely fabricated or if there's some minor truth to it that's being completely misrepresented.
 
Juustin said:
My question is this: Obviously if DNA was able to be "corrected" everytime there was a copying error, it seems like a lot of problems would be cleared up in the world. I just wanted to check in with anyone with more of a genetic/biology background than myself, and see if this statement is completely fabricated or if there's some minor truth to it that's being completely misrepresented.
Click to expand...
Yes, we have mechanisms for correcting most (not every) error in DNA replication; some errors still get past the goalie- allowing evolution.
 
Most mutations are either inconsequential, or harmful, and still most are corrected. The net result is that while mutations rates tend to be low, most mutations that get through suck. A few have been beneficial, even in humans in recent history, such mutations that confer immunity to HIV.
 
Thanks. By the context of the article, and knowing their typical viewpoints, I got the impression that their answer on that seemed a little too simple. I know they're pretty strict creationists, so I wasn't sure if they were wording it in such a way that ruled out any mutations from surviving. I might have been overly suspicious of it, which is why I wanted to double check.

Full article is here: http://www.watchtower.org/e/200605/article_02.htm
 
Juustin said:
My question is this: Obviously if DNA was able to be "corrected" everytime there was a copying error, it seems like a lot of problems would be cleared up in the world. I just wanted to check in with anyone with more of a genetic/biology background than myself, and see if this statement is completely fabricated or if there's some minor truth to it that's being completely misrepresented.
Click to expand...

It is partially correct and partially misrepresented. We (all living cells, in fact) are able to repair the DNA damage which results from 'sloppy' copying. It is when this system fails that we get mutations, and thus variation, and thus evolution.

Here is a press release on Science Daily, and here is the link to the abstract that press report speaks of.

What is wrong about what is being said is that humans would not be "dust" if no DNA repair occured.

ETA: Beaten to it! :o
 
DNA repairWP.

All human beings turn to dust, those without DNA repair mechanisms tend to do it faster than others.
 
P.S. Tangentially, aging is a really complicated subject. There's been a lot of excitement over the discovery of teleomeres, and how cancer cells which do not age and die like other cells have mechanisms that prevent their telomeres from shortening, leading to what appears to be immortality.
 
A quick and dirty guide to DNA replication:

The molecules that perform DNA copying do so with an error rate of about 1/10,000,000. This causes a lot of errors, in the grand scheme of things, when you consider the amount of replications that occur.

However, after the fact there are mechanisms to correct these errors. This accounts for most of them. In addition, there is a very good chance that the error occurred in an inactive region of the DNA molecule, resulting in a net zero phenotypical expression. Lastly, mechanisms to kill off aberrant cells (where the encoding errors have expressed and altered its behavior, cancer being a popular example of this) also exist.

But we do wear down. One reason is the accumulation of these errors. Another reason is that the DNA molecule is truncated after time by all of these replications; the mechanism snips off the end fairly often. Fortunately there is a large "dead" area at the end of the molecule that prevents this from being an issue for quite a while.

I hope this helps, it has been quite a while since my microbiology class, so I can't recall the details of which polymerase does what, or the exact numbers on errors.

H.
 
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