In this video, we're going to talk about protein ubiquitination. Eukaryotes need a way to remove or degrade proteins in a cell that are no longer needed. Recall from our previous lesson videos that cells can utilize post-translational modifications, or PTMs, to tag specific proteins in a cell to be degraded by cellular proteases, the enzymes that degrade proteins. In terms of ubiquitination, ubiquitin is actually a small peptide, a small fragment of protein, that is going to be used by eukaryotic cells to mark other proteins for degradation. We'll be able to see this down below in our image. Now, ubiquitin ligase is an enzyme, a cellular enzyme, that is going to add the ubiquitin peptide to target the protein for degradation. Let's take a look at our image down below to get a better understanding of this. In this example, we're looking at how ubiquitin ligase can add a ubiquitin peptide to misfolded or non-functioning proteins in order to get rid of them and remove them. Once again, this is a type of post-translational modification that occurs in the cytoplasm.

Protein ubiquitination is, basically, what you can see in this image where the mRNA strand is going to be translated into a protein, perhaps an inactive or misfolded non-functioning protein. What can happen is this enzyme, ubiquitin ligase, can take this ubiquitin molecule, this ubiquitin tag, and transfer it over to the tagged protein. Now we have a tagged protein, and this tagged protein has been tagged for degradation by the protease enzyme over here. The protease enzyme can bind to the tagged protein, and that is ultimately going to lead to protein degradation. That will remove the protein that is no longer needed, is non-functioning, or is misfolded. This is a way of regulating gene expression as well, by getting rid of proteins that are no longer needed. This here concludes our brief introduction to protein ubiquitination, and we'll be able to get some practice applying these concepts as we move forward in our course. I'll see you all in our next video.