In this video, we're going to talk about the second level of post-transcriptional regulation, which is mRNA protection in the cytoplasm. mRNA transcripts must be transported to the cytoplasm of the cell in order for the mRNA transcript to be translated by ribosomes and create a protein product. However, the cytoplasm actually has many RNA-degrading enzymes. When mRNA transcripts enter the cytoplasm, they are at risk of being degraded by these RNA-degrading enzymes. These enzymes are there to help destroy foreign viral RNA molecules, acting as a defense mechanism against viral RNAs.
In order for the mRNA transcripts to be protected, the mRNA needs to be processed so that it has a 5' cap added, as well as a poly A tail added at the 3' end of the molecule. This 5' cap and poly A tail protect the mRNA from degradation by enzymes. The process of degradation and protection is a way to regulate gene expression.
Let's take a look at our image down below to get a better understanding. Notice the example here says that mRNA is protected from degradation by cytoplasm enzymes with a 5' cap and a poly A tail. RNA processing, which is the addition of the 5' cap and poly A tail, occurs within the nucleus. But of course, the RNA needs to be transported outside, into the cytoplasm of the cell.
Here, within the cell, we have the nucleus. Inside the nucleus, we have our mature mRNA, which must be transported out of the nucleus. If the mRNA is not protected, if it does not have a 5' cap and a poly A tail, then it is unprotected mRNA, and that leads to degradation. The unprotected mRNA is degraded, and as a result, the final gene product, the protein, is not created. This is a way of turning off the gene.
Conversely, if the RNA is properly protected with the 5' cap and the poly A tail, then we have protected mRNA that will not be degraded. This protected mRNA can then be translated into a protein, and when it's translated into a protein, the final gene product is being made. This is a way of turning on the gene. You can see the off and on states, which are ways of regulating gene expression to turn genes on or off.
This concludes our introduction to this second level of post-transcriptional regulation. We'll be able to get some practice applying these concepts as we move forward, as well as talk about the third and final level of post-transcriptional regulation. So, I'll see you all in that video.