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.
Post Translational Modifications: Videos & Practice Problems
Post-translational modifications are crucial for regulating protein function and gene expression. Key modifications include protein folding, phosphorylation, and ubiquitination. Chaperone proteins assist in proper folding, while kinases and phosphatases add or remove phosphates, often activating or inactivating proteins. Ubiquitination marks proteins for degradation, impacting gene expression. Signal sequences direct proteins to specific cellular locations, and cleavage can initiate significant functional changes. These processes collectively influence the phenotype by determining whether proteins can perform their intended roles.
Post Translational Modifications
Video transcript
Which of the following posttranslational modifications is defined by the addition of phosphates to a protein?
Which of the following posttranslational modifications are removed once a protein arrives at its final destination?
Which of the following posttranslational modifications marks a protein for degradation?
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What are post-translational modifications and why are they important?
Post-translational modifications (PTMs) are chemical changes that occur to proteins after they have been synthesized. These modifications can include the addition or removal of small molecules, such as phosphates, or small proteins like ubiquitin. PTMs are crucial because they regulate protein function, stability, localization, and interaction with other molecules. For example, phosphorylation can activate or deactivate enzymes, while ubiquitination often marks proteins for degradation. These modifications ultimately influence gene expression and cellular function, making them essential for maintaining cellular homeostasis and responding to environmental changes.
Created using AIHow does phosphorylation affect protein function?
Phosphorylation is the addition of a phosphate group to a protein, typically mediated by enzymes called kinases. This modification can significantly alter a protein's function. Generally, phosphorylation activates proteins, enabling them to perform their specific roles, although it can also inactivate some proteins. The removal of phosphate groups, a process called dephosphorylation, is carried out by phosphatases. Phosphorylation can affect a protein's activity, interactions with other molecules, and its localization within the cell. This dynamic regulation is crucial for processes like signal transduction, cell cycle control, and metabolism.
Created using AIWhat role do chaperone proteins play in post-translational modifications?
Chaperone proteins assist in the proper folding of newly synthesized polypeptides into their functional three-dimensional structures. Incorrectly folded proteins can be non-functional or harmful to the cell, so chaperones are essential for maintaining protein quality control. They help prevent misfolding and aggregation, ensuring that proteins achieve their correct conformation. This proper folding is a critical post-translational modification because the function of a protein is highly dependent on its structure. Chaperones also play roles in refolding damaged proteins and targeting irreparably misfolded proteins for degradation.
Created using AIWhat is ubiquitination and how does it influence gene expression?
Ubiquitination is the process of attaching ubiquitin, a small regulatory protein, to a substrate protein. This modification typically marks the protein for degradation by the proteasome, a protein complex responsible for breaking down unneeded or damaged proteins. By regulating the degradation of proteins, ubiquitination influences gene expression. If a protein involved in gene regulation is ubiquitinated and degraded, it can no longer perform its function, thereby affecting the expression of specific genes. This process is crucial for controlling protein levels and ensuring cellular homeostasis.
Created using AIWhat are signal sequences and how do they affect protein localization?
Signal sequences are short peptide sequences within a protein that direct the protein to specific cellular locations. For example, a nuclear localization signal (NLS) directs a protein to the nucleus. Once the protein reaches its destination, the signal sequence is often removed, allowing the protein to perform its intended function. Proper localization is essential for protein function because many proteins need to be in specific cellular compartments to interact with their targets or participate in particular pathways. Mislocalization can lead to loss of function and disease.
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