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

Post Translational Modifications

Hi. In this video, we're going to be talking about post-translational regulation. So far, we've pretty much talked about everything that before transcription that can regulate gene expression, but there are actually a variety of things that can happen post-translation, so after the protein has been made to regulate transcription. And so those types of modifications are going to be on the proteins themselves. So, proteins can be modified by small molecules, or small proteins, or whatever will be added, or taken away from them, and this is going to change their structure or their function. And so there's a bunch of different modifications that can happen. The first modification is how the protein is folded. So incorrectly folded proteins get destroyed, proteins that need to be folded differently for their action can be folded differently at certain time points. And so, chaperone proteins, which are proteins that correctly fold polypeptide chains, are super important in and including phosphorylation, which is the addition of phosphates. This is most commonly connected with the activity of the protein, so usually the addition of a phosphate activates something, the removal of the phosphate inactivates a protein. However, it's not always like that, but generally that's the case. There are proteins called kinases that add phosphates and phosphatases that remove phosphates, and a protein typically isn't only phosphorylated once. It can be phosphorylated 100 and even 1000 times at different amino acids over its whole structure. And so, phosphorylation is a big way that proteins are regulated or activated or deactivated and that affects gene expression because if the protein can't function, we are not going to get expression of that gene. We have ubiquitination, and this is the addition of this protein called ubiquitin, and this actually marks the protein for degradation, obviously affecting gene regulation. If the protein isn't there, it's been degraded, it can't express its phenotype. Other types of modifications include signal sequences. So signal sequences are short peptide sequences, so this is on the protein, and they direct protein to certain cellular locations. So let's say the protein needs to get to the nucleus. Well, it usually contains a signal sequence that directs it to the nucleus, and when it gets to the nucleus, that signal sequence is removed. And so that keeps it there. So like I said, I mentioned the nucleus as the example, that signal sequence is actually called the nuclear localization signal. So this amino acid sequence on the protein says, hey take me to the nucleus. Once it gets there, it gets shut off, and then it can have another function once it's in the nucleus. Super important for gene expression. And then finally another one is called just cleavage, and this is just cutting the protein into kind of pieces. So sections of proteins can be removed and that can change their function. Sometimes cleavage starts an entire cascade of events that can completely change the phenotype of an organism, and it's all initiated by cutting the end of a protein off. And so super important protein modification. Here's an example of ubiquitination and phosphorylation over here. So you can see that this protein here, which is a substrate, has been ubiquitinated 4 different times. So this protein will likely be marked for degradation and degraded, obviously preventing that gene expression because even though it's been transcribed, translated, the protein isn't there, it can't have its function. And then we have phosphorylation, the addition of phosphates, and, yeah this can activate a protein, typically it activates it, will then allow the protein to do whatever it's supposed to do. So these are ways that gene regulation can be regulated after the protein itself has been produced. With that, let's now move on.

Which of the following posttranslational modifications is defined by the addition of phosphates to a protein?

• A. Phosphorylation
• B. Ubiquitination
• C. Signal Sequences
• D. Protein Cleavage

Which of the following posttranslational modifications are removed once a protein arrives at its final destination?

• A. Phosphorylation
• B. Ubiquitination
• C. Signal Sequences
• D. Protein Cleavage

Which of the following posttranslational modifications marks a protein for degradation?

• A. Phosphorylation
• B. Ubiquitination
• C. Signal Sequences
• D. Protein Cleavage