Post-Translational Modification - Online Tutor, Practice Problems & Exam Prep

Post-translational modifications (PTMs) are crucial covalent alterations that regulate protein activity after translation. Key types include methylation (addition of a methyl group), acetylation (addition of an acetyl group), ubiquitination (addition of ubiquitin), and phosphorylation (addition of a phosphate group). These modifications can influence protein function, stability, and interactions, highlighting their importance in cellular processes. Understanding PTMs is essential for grasping protein dynamics and their roles in various biological functions.

Post-Translational Modification

In this video, we're going to begin our lesson on post-translational modifications. First, we need to recall from our previous lesson videos that translation is the cellular process of building proteins by using the encoded messages of messenger RNA or mRNA. Now after translation has been completed and the polypeptide chain has been formed, sometimes post-translational modifications will take place, and post-translational modifications are sometimes abbreviated as PTMs. Now, post-translational modifications or PTMs are covalent proteins activity after translation has been completed. There are many different types of post-translational modifications, and we're going to show you a bunch of post-translational modifications down below in our image.

Some of the more common types of post-translational modifications that you should definitely familiarize yourself with are the four that we have listed down below right here, which are methylation, acetylation, ubiquitination, and phosphorylation. So let's take a look down below at our image to get a better understanding of post-translational modifications. Up here at the top, we're showing you our messenger RNA. And of course, we know that the messenger RNA is going to undergo translation to form our polypeptide chain, our protein whose structure we're showing you right here. Now after translation has been completed this protein, this polypeptide chain can be modified covalently after translation.

And that is why it's called post-translational modification because post means after translation. You can see a bunch of different post-translational modifications that we have listed here. We're showing you nine different post-translational modifications. But you don't need to memorize all of these post-translational modifications. It will depend upon your instructor or your professor which post-translational modifications you should familiarize yourself with.

But the ones that we recommend are here across the top. Here we're showing you hydroxylation, which is the addition of a hydroxyl group. Number 2, what we're showing you is methylation, and methylation is going to be the addition of a methyl group, a \( \text{CH}_3 \) group to the protein, modifying it covalently. Lipidation is going to be the process of adding a lipid to the protein. Acetylation, here, is going to be the process of adding an acetyl group, which you can see here, to the protein.

Then disulfide bonds are another type of post-translational modification that can also occur between the same protein disulfide bonds. Ubiquitination is going to be adding a ubiquitin group to the protein, which is a small protein itself that's going to be added to the protein. Sulfonation is going to be adding a sulfur group, which is represented here as \( S \) to the protein. Glycosylation is going to be adding a carbohydrate to the protein. And then phosphorylation, the last one up here, is going to be adding a phosphate group to the protein after translation.

Once again, there are a bunch of different post-translational modifications. There are a lot more than the ones that we've listed here. And so the ones that you are going to need to know are going to depend on your specific professor, but the ones that we recommend that you should definitely be more familiar with are methylation, acetylation, ubiquitination, and phosphorylation. This here concludes our brief introduction to post-translational modification. 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.

Glycosylation is the post-translational addition of ________ to the protein.

• A. A carbohydrate.
• B. A lipid.
• C. A fat.
• D. A nucleotide.

Which of the following is a reversible form of post-translational modification which can activate or deactivate a protein depending on the protein which is being modified?

• A. Glycosylation.
• B. Ubiquitination.
• C. Acetylation.
• D. Phosphorylation.

Here’s what students ask on this topic:

What are post-translational modifications (PTMs) and why are they important?

Post-translational modifications (PTMs) are covalent alterations to proteins that occur after translation. These modifications can include the addition of functional groups, such as methyl, acetyl, phosphate, or ubiquitin groups, among others. PTMs are crucial because they regulate protein activity, stability, localization, and interactions. By modifying proteins, PTMs can influence various cellular processes, including signal transduction, gene expression, and protein degradation. Understanding PTMs is essential for grasping how proteins function dynamically within cells and how they contribute to different biological functions and disease mechanisms.

What are the common types of post-translational modifications?

Common types of post-translational modifications (PTMs) include methylation, acetylation, ubiquitination, and phosphorylation. Methylation involves the addition of a methyl group (CH₃) to a protein. Acetylation is the addition of an acetyl group (COCH₃). Ubiquitination involves attaching ubiquitin, a small protein, to a target protein. Phosphorylation is the addition of a phosphate group (PO₄^3-). These modifications can alter protein function, stability, and interactions, playing critical roles in cellular processes such as signal transduction, gene expression, and protein degradation.

How does phosphorylation affect protein function?

Phosphorylation, the addition of a phosphate group (PO₄^3-) to a protein, typically occurs on serine, threonine, or tyrosine residues. This modification can significantly alter a protein's function by changing its conformation, activity, or interactions with other molecules. Phosphorylation often acts as a molecular switch, turning protein activity on or off, and is crucial in regulating cellular processes such as signal transduction, cell cycle progression, and metabolic pathways. It is a reversible modification, allowing dynamic control over protein function in response to cellular signals.

What is ubiquitination and what role does it play in the cell?

Ubiquitination is the process of attaching ubiquitin, a small regulatory protein, to a target protein. This modification typically tags proteins for degradation by the proteasome, a protein complex responsible for breaking down and recycling proteins. Ubiquitination plays a critical role in maintaining protein homeostasis, regulating protein turnover, and controlling various cellular processes such as cell cycle progression, DNA repair, and signal transduction. By marking damaged or unneeded proteins for degradation, ubiquitination helps maintain cellular function and prevent the accumulation of potentially harmful proteins.

What is the difference between methylation and acetylation in post-translational modifications?

Methylation and acetylation are both post-translational modifications that involve the addition of specific chemical groups to proteins. Methylation is the addition of a methyl group (CH₃) to amino acid residues, typically lysine or arginine. This modification can affect protein interactions and gene expression by altering chromatin structure. Acetylation involves adding an acetyl group (COCH₃) to lysine residues, often on histone proteins. Acetylation generally reduces the positive charge on histones, leading to a more relaxed chromatin structure and increased gene transcription. Both modifications play crucial roles in regulating protein function and gene expression.