Mutation Monday (Your Mutation Station): Thymine dimers

by Rich Feldenberg

Welcome back to your mutation station.  Today we'll look at a harmful effect on your DNA due to ultraviolet light, which leads to dimerization of the nucleotide bases thymine (T).  If there are two T bases next to each other in the DNA strand and they absorb UV light they can undergo a photochemical reaction that causes them to link-up.   The double bonds in the base break and then form single bonds to their neighbor.

This blocks normal base pairing on to the other DNA strand of the double helix, and results in a mutation.  Fortunately there are cellular repair mechanisms that can find and fix these errors, but some errors escape detection and cause major harm.  Some melanomas are thought to be due to thyimine dimers caused by the effect of UV sunlight.

Thymine dimers are actually a more specific form of what is called pyrimidine dimers.  The bases thymine and cytosine (T and C) are pyrimidines.  Two pyrimidines can dimerize under the same conditions leading to the same sort of DNA mutations.  You could have T-T dimers (thymine dimers), but also T-C, and C-C leading to the same problems.   So, remember to use sunblock and be careful about exposure to the sun!!

Origins Sunday: Evolution of life's first proteins

Check the link below for some cool research in the origin of life on earth!!
Evidence of key ingredient during the dawn of life

Fossil Friday: Dickinsonia

by Rich Feldenberg

Welcome to the long forgotten Ediacaran Period (635-542 Million years ago) in the Precambrian.  An assortment of unusual and fascinating fossils have been found dating to this time period, when multicellular life was just getting large enough to make good fossil imprints.  It is sometimes known as "The Garden of Ediacaran" because it is thought that at this early stage of animal evolution most creatures were basically filter feeders, and no major predation had yet developed (including the tools used by predators such as teeth, eyes, or sophisticated brains).  In that sense it may have been a very peaceful and "innocent" chapter in the history of life, before an evolutionary arms race between predator and prey began in the Cambrian and continues on to this day.

One common fossil found in rocks of this age is that of Dickinsonia.  This little guy was round shaped with a bilateral symmetry - something that shows some level of sophistication from the even earlier radially symmetric ancestors.  It seems to have had a head-end and a tail-end and was divided into segments.  It is not clear what kind of animal Dickinsonia really was, and there is a great bit of controversy in the scientific community in regards to its proper placement on the tree of life.  It seems to have been capable of movement over the ocean floor, as there have been fossilized tracts found that are thought due to its movements.   It may have belonged to a phyla that went extinct by the end of the Ediacaran period, or alternatively it may be related to modern day creatures.  Some experts have speculated that it is related to modern day jellyfish and some even think it may be related to animals that eventually became vertebrates.  Others have even gone so far as to say that it was not an animal at all, but part of a short lived, and ultimately unsuccessful evolutionary experiment in some type of multicellular life form that went extinct half a billion years ago.  What ever Dickinsonia was it made beautiful fossils!