Genome complexity: DNA repair a saltation? (Introduction)

by David Turell , Friday, February 03, 2017, 01:34 (2638 days ago) @ David Turell

There are two methods to repair broken DNA, one of which employs enzymes:

https://www.sciencedaily.com/releases/2017/02/170202085851.htm

The results are significant for gene therapy procedures and for our understanding of cell transformation. A team of researchers has discovered that the processes for repairing DNA damage are far more complex than previously assumed. The ends of breaks in the double helix are not just joined, they are first changed in a meticulously choreographed process so that the original genetic information can be restored.

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Over the course of evolution, ways to repair this DNA damage have developed, in which many enzymes work together to restore the genetic information with the maximum possible precision.

As it stands today, there are two main ways of repairing DNA double-strand breaks, which differ greatly in terms of their precision and complexity. The apparently simpler method, so-called non-homologous end joining, joins together the break ends as quickly as possible, without placing particular importance on accurately restoring the damaged genetic information. The second method of repair, homologous recombination, on the other hand, uses the exactly identical information present on a sister copy to repair the damaged DNA with great precision. However, such sister copies are only present in dividing cells, as the genetic information has to be duplicated before the cells divide. But most cells in the human body do not undergo division, which therefore assigns them to the apparently more inaccurate method of end joining.

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We found it difficult to understand how it was that important genetic information could get lost during the non-homologous end joining repair process." As a result, the research teams examined the enzymatic processes occurring at the breaks before they join together -- with surprising results. In contrast to previous schools of thought, the break ends are not simply joining together, but are being changed by specific enzymes, so that the information that was lost as a result of the break could be identically repaired with the aid of a copy.

These changes at the break ends -- called "resection" in the lingo -- are highly reminiscent of the homologous recombination process, where a sister copy acts as a matrix for precise repair. It is just that in non-dividing cells, there is no sister copy of the DNA, so at present it is still unclear where the copy of the genetic information necessary for precise repair could actually come from. However, the new findings provide clear evidence that cells that do not divide also use copies of genetic information to repair DNA double-strand breaks.

Comment: DNA is an intricate code, beyond any invented by humans. There must be exac t copies as cells divide. The first cells of life had to copy exactly or life would not have lasted. The repair mechanism had to appear at the point of origin of the DNA code. An obvious saltation by a brilliant mind. Nothing else fits, does it?