Distillation sketch—rapid control of gene expression
A distillation sketch is like an artistic sketch or musical jam session. Which version below do you prefer, and why?
My new version:
When you’re starving or exercising intensely, your body needs to make more energy, but there’s not much glucose or glycogen left to do it with. So it sends a signal to your liver cells to start breaking down other molecules, like amino acids and small molecules, and turning them into glucose, which can in turn be broken down for energy. Cortisol is the hormone that carries that signal to the liver.
However, your body also needs to avoid spending all that energy until the critical moment. So it has a transcription regulator, GRP (the aptly named “glucocorticoid receptor protein”), lying in wait in the liver.
Normally, GRP alone can’t bind DNA. But when it binds with cortisol and activates, it causes transcription of genes for enzymes critical for glucose production from these alternative sources. Tyrosine aminotransferase is one such enzyme. Though these genes are regulated in all sorts of different and complicated ways, they all need GRP to bind their cis-regulatory sequence in order to be transcribed at top speed.
When the body calms down and cortisol goes away, GRP releases, and these glucose production genes drop back down to normal expression.
Original (Molecular Biology of the Cell, Sixth Edition by Alberts and Bruce):
An example is the rapid control of gene expression by the human glucocorticoid receptor protein. To bind to its cis-regulatory sequences in the genome, this transcription regulator must first form a complex with a molecule of a glucocorticoid steroid hormone, such as cortisol. The body releases this hormone during times of starvation and intense physical activity, and among its other activities, it stimulates liver cells to increase the production of glucose from amino acids and other small molecules. To respond in this way, liver cells increase the expression of many different genes that code for metabolic enzymes, such as tyrosine aminotransferase, as we discussed earlier in this chapter. Although these genes all have different and complex control regions, their maximal expression depends on the binding of the hormone–glucocorticoid receptor complex to its cis-regulatory sequence, which is present in the control region of each gene. When the body has recovered and the hormone is no longer present, the expression of each of these genes drops to its normal level in the liver. In this way, a single transcription regulator can rapidly control the expression of many different genes.
Distillation sketch—rapid control of gene expression
A distillation sketch is like an artistic sketch or musical jam session. Which version below do you prefer, and why?
My new version:
Original (Molecular Biology of the Cell, Sixth Edition by Alberts and Bruce):