Genome and evolvability: a DNA timer for mutations (Introduction)

by David Turell , Monday, February 05, 2018, 20:12 (2482 days ago) @ David Turell

A mechanism that allows for copy mistake mutations is found. This will drive the process of evolution:

https://www.sciencedaily.com/releases/2018/01/180131133343.htm

"Scientists have discovered that the helical structure of DNA contains a kind of built-in timer that determines the frequency at which specific mutations spontaneously occur. They show that certain DNA bases can shape-shift for a thousandth of a second, transiently morphing into alternative states that can allow the replication machinery to incorporate the wrong base pairs into its double helix. Such mismatches, though rare, could serve as the basis of genetic changes that drive evolution and diseases, including cancer.

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"The study, published in a 2015 issue of Nature, showed the bases G and T nudging aside the atoms on their surface so they could connect like puzzle pieces. The researchers found that these rearrangements came in different varieties, called "tautomeric" and "anionic" forms, though it wasn't clear which ones were responsible for replication errors.

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"Together with their collaborators at The Ohio State University, they fed their NMR data into a "kinetic model" that traced the nearly invisible movements taken by the atoms in the mismatches that result in replication errors. They found that, though the different alternative states each contributed to errors, the tautomeric forms dominated under normal conditions and the anionic forms dominated in the presence of mutagens and environmental stress.

"'In the past, we knew DNA polymerases make mistakes during DNA replication but did not know how they do it," said Zucai Suo, Ph.D., Ohio State professor of chemistry and biochemistry. "Now, our study provides a mechanistic sense for how the mistakes arise."

"The results provide "convincing validation for the chemical origins of mutations proposed by Watson and Crick in 1953," said Myron Goodman, Ph.D., a professor of molecular biology and chemistry at the University of Southern California, who was not involved in the study. "It is significant scientifically, and even though it took about 65 years to prove, it also demonstrates the folly of ever betting against Watson and Crick."

"The textbook depiction of the iconic double helix shows a static double-stranded structure, but it turns out that on rare occasions it can morph into other shapes that exist for exceptionally small periods of time," Al-Hashimi said. "Though some might question the importance of such states, there are a growing number of studies showing they can be major drivers of biology and disease.

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"One of the surprising discoveries made by the team was that the frequency at which bases shifted their shapes varied with DNA sequence. In one of their experiments, Ohio State biochemists Zucai Suo and Walter Zahurancik essentially counted the number of times that polymerases incorporated the wrong base into the DNA. They found that mistakes were indeed not uniform: they appeared more frequently in some sequences than others. For example, a region with more Gs and Cs might form more quantum jitters, and subsequently more mutations, than an area that was rich in As and Ts.

"The quantum jitters may be responsible not only for errors in replication, but also in other molecular processes such as transcription, translation, and DNA repair."

Comment: If God designed how DNA works, He would have certainly put in this mechanism to drive evolution.