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Wednesday, July 27, 2011


A report in ScienceDaily shows how fine-tuned biological logic can be--even down to the way a single electron is used in a strange but smart way to achieve the desired result with maximum efficiency.

The enzyme photolyase, which is naturally produced in the cells of plants and some animals (but not in mammals, including humans) repairs DNA by damaged by sunlight by tearing open the misshapen, damaged area in two places and reforming it into its original, undamaged shape.

But the enzyme does not break up the injury in both pieces at once. It is a two-step process that sends a single electron through the DNA molecule in a circuitous route from one breakup site to another.

Ultraviolet (UV) light damages DNA by exciting the atoms in the DNA molecule, causing accidental bonds to form between the atoms. The bond is called a photo-lesion, and can lead to a kind of molecular injury called a dimer. Dimers prevent DNA from replicating properly, and cause genetic mutations that lead to diseases such as cancer.

The dimer in question is called a cyclobutane pyrimidine dimer, and it is shaped like a ring that juts out from the side of the DNA.

For those organisms lucky enough to have photolyase in their cells, the enzyme absorbs energy from visible light--specifically, blue light--to shoot an electron into the cyclobutane ring to break it up. The result is a perfectly repaired strand of DNA.