Photoreactivation

Our cell's DNA is continuously replicated in order to grow, maintain and repair tissues within our bodies. Although this process is repeated many millions of times daily, the rate of error of replication of our genetic material is surprisingly low. So how is this possible? As humans have evolved into increasingly complex organisms, biological repair mechanisms which mend damaged DNA have made it possible for us to pass on our genetic material to future generations with high accuracy, therefore increasing our chances of survival as a species.

One way to repair damaged DNA is to reverse it directly, consequently regenerating the correct base pair. An example of this is in the repair of a mutagenic photodimer between two pyrimidines caused by UV light (265-300nm). An enzyme, called photolyase, binds to the photodimer which breaks the bonds in the presence of specific wavelengths of visible light, which restores the initial base pairs. This process is called photoreactivation. The enzyme photolyase is unable to function without visible light (300-600nm), and therefore alternative DNA-repair mechanisms are responsible in the absence of visible light.