Several decades ago, the cellular process known as “DNA repair” was not even suspected. But since then, investigation of genetic functions has increasingly revealed a system that is mind-bogglingly elegant, minute, and effective.
A suite of several dozen proteins are active in our cells, each of which plays an integral role in the repair of damaged DNA. They include DNA Ligase, PCNA (a sliding clamp), and p53 and p21, which signal the appropriate DNA repair enzyme clamps to the corrupted DNA at the right place and time. There are also enzymes “tailored to deal with certain specific types of DNA damage,” as well as over 200 proteins peripheral to DNA damage detection and repair.1
Properly-functioning DNA repair mechanisms are important because they constantly combat the relentless accumulation of mutations that occurs from the jostling of molecules. Without a repair system in place, it is likely that excessive mutations would have dramatically shortened our lifespans, and would have caused our extinction long ago.2
A new DNA repair enzyme has been accurately modeled and its vital function discovered.3 The enzyme, Rtt109, ensures a bit of “slack” in what would otherwise be tightly-spooled DNA. Only if the DNA has the correct amount of slack in the right place will the other necessary repair enzymes have enough space to access and clamp onto the DNA properly.
If we postulate that new biological structures arise from the selection of genetic mistakes, called mutations, and that this process has resulted in the life functions we currently observe, then we have an enigma: random genetic mistakes created specific enzyme systems which operate with sequential coordination. With each new biochemical discovery, our picture of the complexity of cells grows.
Biologists of the 1800s thought of cells as simple blobs of protoplasm. We have since learned that cells contain armies of elegant and dazzling miniaturized motors.4 This evidence of complex, purposeful function is so compelling that it begs the question: if Charles Darwin had known what we know now, would he have even bothered to proffer a naturalistic mechanism for the formation of life?
- Weizmann Institute scientists discover a molecular security mechanism for keeping mutations in check. Weizmann Institute of Science press release, May 4, 2006.
- See Demick, D. 1999. The Blind Gunman. Acts & Facts. 28 (2).
- Researchers solve structure of an enzyme vital for DNA repair. Rockefeller University press release, August 11, 2008. Accessed on newswire.rockefeller.edu August 14, 2008.
This is well illustrated in “Molecular Visualizations of DNA,” a computer animation created by Drew Berry of the Walter and Eliza Hall Institute of Medical Research. A copy posted on YouTube.com on May 8, 2008 was available at the writing of this article through the following URL: http://www.youtube.com/watch?v=4PKjF7Oum
* Mr. Thomas is Science Writer.
Article posted on August 27, 2008.