Ultraviolet - Evolutionary Significance

Evolutionary Significance

Evolution of early reproductive proteins and enzymes is attributed in modern models of evolutionary theory to ultraviolet light. UVB light causes thymine base pairs next to each other in genetic sequences to bond together into thymine dimers, a disruption in the strand that reproductive enzymes cannot copy (see picture above). This leads to frameshifting during genetic replication and protein synthesis, usually killing the organism. As early prokaryotes began to approach the surface of the ancient oceans, before the protective ozone layer had formed, blocking out most wavelengths of UV light, they almost invariably died out. The few that survived had developed enzymes that verified the genetic material and broke up thymine dimer bonds, known as base excision repair enzymes. Many enzymes and proteins involved in modern mitosis and meiosis are similar to excision repair enzymes, and are believed to be evolved modifications of the enzymes originally used to overcome UV light.