Protein clock dating
So cells have a way of synchronizing their clocks with the outside world.
The clock in our brain is synchronized by exposure to light.
The phosphates that tick off the hours of each day are added to a serine and a threonine on each subunit.
They are buried deep inside the tunnel, near the binding site for ATP, shown here in green.
The 24-hour oscillation of the levels of these proteins is controlled by a series of interconnected feedback loops, where the levels of the proteins precisely regulate their own production.
A much simpler system has been discovered in cyanobacteria.
But surprisingly, different organisms have evolved many different ways of doing this.
Animal cells use a complex collection of proteins (with fanciful names like Clock, Cryptochrome, and Period) that are rhythmically synthesized and degraded each day.
In order to calculate the rate at which a stretch of DNA changes, biologists must use dates estimated from other relative and absolute dating techniques.Our cells contain tiny molecular clocks that measure out a 24-hour circadian rhythm.This clock decides when we get hungry and when we get sleepy.It acts as our central pacemaker, checking the cycles of light and dark outside, and then sending signals to synchronize clocks throughout the rest of the body.Molecular processes occur so fast that is it difficult to imagine a 24-hour clock that works at the molecular level.