Post Translational Modification - Video Tutorials & Practice Problems
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Post Translational Modification
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So in this video, we're going to continue to talk about ways that cells can regulate their biochemical reactions by introducing post translational modifications. And so recall from our previous lesson videos that translation is the cellular process of building proteins by using the encoded messages of mRNA. And so the prefix post actually means after. And so like a post game interview is an interview after the game, post translational modifications are just protein covalent alterations that specifically control protein activity and take place after translation. And so post translational modifications are sometimes abbreviated as just PTMs, and it turns out that there are many different types of post translational modifications, several 100 for that matter, and so we're not going to be able to cover all of the different types of post translational modifications in our course. But there are some more common types of post translational modifications that we expect your professors might want you guys to know about. And these include methylation, acetylation, ubiquitination, and phosphorylation. And so down below in our example, we're showing you guys just a small handful of some post translational modifications. And so notice, towards the top of our image over here, what we have is this pink squiggly line, which represents our mRNA molecule. And this pink arrow going downwards right here represents the process of translation. And so translation is, going to build our protein molecule, which is right here, using the encoded messages of mRNA, just like what we mentioned up above. And so, again, any covalent modification that occurs to this protein after the process of translation is referred to as a post translational modification. And again, there are many different types of post translational modification. So these are definitely not all of them here and we're only showing you a small handful. Nine of them, to be specific. And so the first post translational modification that we're showing you guys is hydroxylation. And hydroxylation is just the process of taking our pro protein and covalently adding a hydroxyl group to it. So hydroxylation adds a hydroxyl group. Now if we take our protein and instead of adding a hydroxyl group, we add a methyl group like this 1, a CH3, that is is referred to as the process of methylation, which is, pretty straightforward, just adding a simple methyl group. Now, if we take our protein and we add a lipid to it, it's referred to as lipidation, and lipids tend to have these large hydrocarbons like this one right here. Now, if we take our protein and covalently add an acetyl group, like this functional group right here, this is referred to as acetylation. Now, moving on to our next post translational modification, what we have are disulfide bonds which we have talked about before in our previous lesson videos. And so we know that disulfide bonds will form between the R groups of 2 cysteine amino acid residues linking, potentially linking 2 separate polypeptide chains. Now, the next post translational modification that we have here is ubiquitination. And ubiquitination, we will talk about more as we move forward in our course, but really it's just this process of taking a protein and covalently adding a small protein to it, called ubiquitin. Now, the next post translational modification is sulfonation, which is adding a sulfate group to the protein. And then we have glycosylation, which is adding a carbohydrate to our hydrate to our protein. And then last but not least, what we have up here is phosphorylation. Phosphorylation. And, phosphorylation we will also talk more about later in our course, and it's simply the process of adding a phosphate group to our protein. And so this here concludes our introduction to post translational modifications. And, as we move forward in our course, we're going to continue to talk about very select types of post translational modification. So, I'll see you guys in our next video.
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concept
Post Translational Modification
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2m
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Video transcript
So another type of post translational modification that your professors might expect you guys to know about that we didn't cover in our last lesson video is proteolytic cleavage. And so proteolytic cleavage is just the process of breaking down peptide bonds between the amino acid residues of proteins. And so, of course, this process of proteolytic cleavage is going to require proteases or peptidases, which we've already covered in our previous lesson video. So we know that peptidases or proteases are just enzymes that cleave peptide bonds at very, between very specific amino acid residues. And so notice down below in our image here on the left hand side, what we have is our protein immediately after translation. And so some proteins immediately after translation are actually inactive, and so they do not work and cannot perform their job when they are in this inactive form. And so in order to activate the protein, some proteins need to go through the process of proteolytic cleavage. And so this arrow right here represents the process of proteolytic cleavage, which is going to require a protease or a peptidase that's essentially going to act like molecular scissors and cut our protein. And, essentially what that's going to do is it's going to activate, our protein. And so here what we have is the active form of our protein, and, sometimes that can also generate inactive forms of our protein or cleave off inactive forms of our protein. Now, here in this image, since I put together this image here, it looks like I took a hacksaw and just cut straight down the middle of our protein right here to cut it in half. But, essentially, that explains why I'm not a protease, but, we can get the point here that proteases are going to cleave some specific peptide bonds in order to activate our protein and, potentially cleave off other inactive forms, from the protein. And so we'll be able to talk even more about proteolytic cleavage later in our course when we're talking about zymogens. But for now, this concludes our introduction to proteolytic cleavage, and we'll be able to get some practice, with the concepts that we've learned as we move forward in our course. So I'll see you guys in our next video.
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Problem
Problem
Which of the following would not be a reversible post-translational modification?
A
Phosphorylation.
B
Preoteolytic processing.
C
Alkylation.
D
Methylation.
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Problem
Problem
An enzyme's active site has high affinity for a polar charged substrate. How will methylation of the active site affect the reaction rate of the enzyme?
A
Affinity for the charged substrate will increase thereby increasing reaction rate.
B
Affinity will remain unchanged, and therefore will be independent of the modification.
C
Affinity for the substrate will decrease, lowing the reaction rate.
5
Problem
Problem
Histones are proteins that regulate gene expression by binding to DNA and controlling which regions are exposed to be expressed. Histones bind to DNA at a neutral pH via their positively charged lysine residues, but acetylation of histones leads to the dissociation of the DNA-Histone complex. Covalent modification of lysine's ammonium group by acetylation results in an overall _______________ charge of the histone binding region.