Eukaryotic Post-Translational Regulation: Study with Video Lessons, Practice Problems & Examples

Eukaryotic cells regulate protein activity through post-translational modifications (PTMs), which are covalent changes made after translation. These modifications can activate or inactivate proteins, or tag them for degradation by proteases. Ubiquitination, a specific PTM, involves adding ubiquitin to misfolded proteins via ubiquitin ligase, marking them for degradation. This process is crucial for maintaining cellular function and regulating gene expression by removing unnecessary proteins, thus ensuring cellular homeostasis and efficiency.

Eukaryotic Post-Translational Regulation

In this video, we're going to begin our lesson on eukaryotic post-translational regulation. And so eukaryotes can regulate expression at the post-translational level by controlling the activity of the expressed protein. Recall from our previous lesson videos that post-translational modifications can be abbreviated as PTMs. And really they are defined as covalent modifications to proteins after translation takes place, and that is what the post, root here is referring to. Post is referring to after. Now these post-translational modifications or PTMs, they can either activate or inactivate a protein depending on the specific protein in the specific scenario. Or they can actually tag the protein or mark the protein for degradation by proteases. And so proteases are specific enzymes that are going to degrade proteins by breaking polypeptide bonds, the bonds that link amino acids together. By degrading proteins, by breaking polypeptide bonds, they're capable of making single amino acids. If we take a look at our image down below, we can get a better understanding of these post-translational modifications. Protein activity can be controlled by post-translational modifications or the degradation by proteases. Taking a look at our little mini map over here, what you'll notice is post-translational protein modifications occur in the cytoplasm of the cell. Up above, what we're showing you is the mRNA here that's going to be translated into a protein. But in many cases, proteins that are initially translated can be inactive proteins. The post-translational modification here includes, this modification tag, basically covalently modifying the protein to create an active protein. This is a form of turning on gene expression to ensure that there is an active protein product. Again, this is through post-translational modification, a modification that occurs after translation has occurred. Now, again, post-translational modifications can inactivate a protein as well. So it's also a form of turning off a gene. Down below what we're showing you is, again, an mRNA being translated into a protein. And this time, there is again a modificational tag being added to the protein. But this time, this tag is actually marking the protein for degradation by this protease enzyme. And this protease enzyme in blue is going to perform protein degradation to break up that protein into individual amino acids. Of course, if we are degrading the protein, then that is a form of turning off the gene. It's a form of regulation. You can see here that through post-translational modifications, proteins can be turned on and or proteins can be turned off depending on the specific scenario. This here concludes our brief introduction to eukaryotic post-transitional regulation, and we'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you all in our next video.

Protein degradation is one strategy to control gene expression and is considered ______.

• A. Transcriptional control.
• B. Post-transcriptional control.
• C. Translation initiation control.
• D. Post-translational control.
• E. Chromatin remodeling.

Post-translational modifications of proteins can affect which of the following?

• A. Protein function.
• B. Protein location within the cell.
• C. Protein activation or inactivation.
• D. Protein degradation.
• E. All of the above.

Protein Ubiquitination

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.

A hormone signal reaches a cell and causes the cell to produce a large quantity of Protein X. After some time, the hormone signal disappears and the cell no longer needs a large quantity of Protein X. How will the cell remove the excess protein?

• A. The repressor protein for the Protein X gene will stop the transcription of the gene.
• B. The excess Protein X will be tagged with ubiquitin proteins and degraded over time.
• C. The Protein X mRNA will be bound by a microRNA blocking its translation.
• D. Over time the excess Protein X will diffuse out of the cell.

Here’s what students ask on this topic:

What are post-translational modifications (PTMs) in eukaryotic cells?

Post-translational modifications (PTMs) in eukaryotic cells are covalent modifications that occur to proteins after they have been synthesized during translation. These modifications can include the addition of functional groups, such as phosphate or methyl groups, or the attachment of small proteins like ubiquitin. PTMs can activate or inactivate proteins, alter their stability, localization, or interaction with other molecules, and are crucial for regulating protein function and cellular processes. Examples of PTMs include phosphorylation, glycosylation, acetylation, and ubiquitination.

How does ubiquitination regulate protein degradation in eukaryotic cells?

Ubiquitination is a post-translational modification where a small protein called ubiquitin is attached to a target protein by the enzyme ubiquitin ligase. This process tags the protein for degradation by the proteasome, a complex that breaks down proteins into amino acids. Ubiquitination is essential for removing misfolded, damaged, or unneeded proteins, thereby regulating protein levels and maintaining cellular homeostasis. By controlling protein degradation, ubiquitination plays a critical role in gene expression, cell cycle regulation, and response to stress.

What role do proteases play in post-translational regulation?

Proteases are enzymes that degrade proteins by breaking peptide bonds, converting them into smaller peptides or amino acids. In post-translational regulation, proteases are involved in the degradation of proteins that have been tagged for destruction, often through ubiquitination. This process helps regulate protein levels, remove damaged or misfolded proteins, and control various cellular functions. By degrading specific proteins, proteases play a crucial role in maintaining cellular homeostasis and regulating gene expression.

What is the significance of protein ubiquitination in cellular function?

Protein ubiquitination is significant in cellular function because it regulates the degradation of proteins, ensuring that damaged, misfolded, or unnecessary proteins are removed. This process is vital for maintaining protein quality control, regulating the cell cycle, and modulating various signaling pathways. Ubiquitination also plays a role in immune responses, DNA repair, and apoptosis. By controlling protein turnover, ubiquitination helps maintain cellular homeostasis and proper cellular function.

How do post-translational modifications affect protein activity?

Post-translational modifications (PTMs) affect protein activity by altering the protein's structure, stability, localization, or interactions with other molecules. For example, phosphorylation can activate or deactivate enzymes, glycosylation can affect protein folding and stability, and ubiquitination can target proteins for degradation. These modifications allow cells to rapidly respond to changes in the environment and regulate various cellular processes, including signal transduction, gene expression, and metabolism.