Now, these regulatory molecules aren't permanently bound to the promoter.
They can come off and then back on again, and off and on again, so
the genes in your cells are switched on and off, and on again,
in a very subtle, choreographed dance that maintains the functions of life.
All the cells in your genome have the same genes, but
different cells produce different regulators that bind to different genes.
So a liver cell is only gonna produce liver proteins, and a kidney cell is only
gonna produce the proteins necessary to make it a kidney cell.
So very crudely then, the switch on the wall is the promoter, your finger
is the regulator and gene expression is the light turning on and off.
Now, Dr. O'Brien has mentioned, as well as promoters,
your genome also has about 400,000 enhancers that can influence
the activity of genes, sometimes across great distances.
Enhancers also have docking sites for regulatory molecules,
usually proteins again.
And then you've got other types of proteins on the DNA which can actually
physically move the enhancer DNA, loop the enhancer DNA, so the enhancer and
its regulators are brought into contact with a promoter.
And just as I was mentioning when talking about promoters,
different cells produce different regulatory proteins for the enhancers.
Perhaps cell A creates a protein that binds to one of these enhancers, and
what that protein would do is it would get the DNA to fold and come to interact
with the promoter and cause high-level expression of a particular gene.
And another cell, cell B, won't be making that regulatory protein, and so
it won't express the same gene.
It's very, very complicated.
That's kind of what I'm trying to get through to you here.
It's an extremely complicated process.