Protein clock dating
To explore this structure in more detail, click on the image for an interactive JSmol. Goodsell (The Scripps Research Institute and the RCSB PDB) presents short accounts on selected molecules from the Protein Data Bank.Each installment includes an introduction to the structure and function of the molecule, a discussion of the relevance of the molecule to human health and welfare, and suggestions for how visitors might view these structures and access further details.The daily rise and fall of melatonin is caused by changes in the levels of the enzyme serotonin N-acetyltransferase, shown here from PDB entry .This enzyme adds a few atoms to the neurotransmitter serotonin, then a second enzyme converts it into melatonin.Kai A stimulates Kai C to add these phosphate groups to itself, and Kai B blocks the action of Kai A, allowing Kai C to remove these phosphates from itself.The speed of these reactions are all calibrated so that the whole process takes 24 hours to complete.
Since each lineage experienced its own evolution, the two species must have descended from a common ancestor that lived at least 50 million years ago.
The small hormone melatonin is produced selectively at night, and circulates through the blood to coordinate our nightly activities, such as sleep.
Treatment with melatonin may be used to change this cycle artificially, for instance helping to shift cycles that are out of phase during jet lag.
When a stretch of DNA does indeed behave like a molecular clock, it becomes a powerful tool for estimating the dates of lineage-splitting events.
For example, imagine that a length of DNA found in two species differs by four bases (as shown below) and we know that this entire length of DNA changes at a rate of approximately one base per 25 million years.