This is the last week of my Fall 2012 General Biology class and we have finally gotten to the material I look forward to all year.
Throughout the semester we build towards an understanding of the central dogma (DNA –> RNA –> Protein). Early on we are introduced to this idea and are given the basics that DNA is the information that is required to build cells; which are made of these proteins as well as some other biomolecules. It’s easy to have a protein-centric view of the cell because these molecules provide structure to the cell and accomplish many of the functions of the cell by acting as receptors, enzymes, signaling molecules, etc. (This is an over-simplification, but one I can live with)
Last week we focused on the details of transcription and translation and how these molecular processes read information from DNA to make an mRNA ‘message’ that leaves the nucleus and goes to the cytoplasm where translation of this message results in the production of a protein with the specified amino acid (AA) sequence.
This segued into what happens when there are errors or mutations along the way. Because the AA sequence of the protein is determined directly from what is encoded in the DNA, changes is DNA may have direct consequences on the protein. Another central idea I teach is ‘Form Dictates Function.’ Because the form of a protein is determined by the AA sequence, changes in sequence mean changes in form and therefore changes in function.
So, how does this relate to my opening question, ‘What kind of planet do we live on?’
The process illustrated by the central dogma is fairly faithful. Most often the proteins are NOT mutated and are made just as the DNA directs and they function as expected. However, once in a while, mutations come in and hit the DNA and there is suddenly a DNA change leads to a change in the RNA, that leads to a change in the AA sequence, that leads to a new folding of the protein. This may provide a benefit (very rarely) or may cause a problem (more commonly). If it confers a benefit, this provides an advantage to the bearer of these new proteins and they may be more successful living longer and leaving more children. If it is detrimental, then the bearer may not live as long and may have few, if any, children.
But this is a SLOW process.
If the world was 4000 years old, this process could not conceivably explain the diversity of life on Earth. But if the world is 4.5 BILLION years old, that may be enough time. Darwin struggled with this idea and it was not until he witnessed the wide world during his voyage aboard the HMS Beagle that he started to see evidence that the world was much older than he once suspected.
One of the first suggestions that Darwin say about the history of the Earth was the presence of sea fossils high in the Andes Mountains. How could this be? These could only make sense if the mountains were not always mountains, but the Earth changed over time.
With the idea of ‘deep time’, meaning that the Earth is very, very old – on the order of Billions of years – Darwin’s idea of mutations accumulating over time as fuel for evolution becomes plausible.
What kind of planet do we live on?
A very old , changing planet