4. Protein Structure
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So at this point, we've covered from primary protein structure all the way up through tertiary protein structure. Now, before we get to Quaternary protein structure, there are few topics that we need to talk about. And one of those topics is de nature ation, so we'll talk about that now. So D nature ation is just the process of disrupting a protein's structure. And specifically we're talking about disrupting the protein, secondary or tertiary structure just enough to cause a loss of protein function so a denatured protein will not be able to perform its job. And so one thing that's not affected by Dean a tray shin is the primary protein structure. So the primary protein structure, or the composition and sequence of the amino acids, is not affected by de nature Ation. Now D nature ation can result from several different factors, from radiation to changes in temperature or even changes in pH. And it can even result from the addition of re agents that affect structure. And we'll talk about some of those re agents in our next lesson video. Now Renate aeration is actually the reverse process of de nature ation. So this is the process where we can take a denatured protein and regain the proteins original structure and shape. And so, in our example below, we're gonna distinguish between Dean H. Eurasian and Renate Oration. So what we have on the left over here is a normal protein shape. And so our normal protein shape has normal biological activity. That means that it does its job properly. Now, if we take this normal protein and we go through a process that d nature's the protein. So we d nature, this protein, what we end up getting is a denatured protein shape and so notice that it's lost a lot of its structure. So the Alfa he leases that were present over here and some of the beta sheets and all of these turns and stuff like that. Ah, lot of that structure has been lost, so mostly secondary and tertiary structure. But again, the primary protein structure is still intact. So we still have our in terminal end and R C. Terminal end and the order and sequence and composition of amino acids are all still fine. When a protein is denatured but are denatured protein has now lost all of its biological activity, which means that it cannot perform its function anymore. Now, if we take our denatured protein and we go through a process of re nature ation, that would be the reverse process of de nature rations. So that's taking are denatured protein and regaining its original shape and function. So that would be the process of going from this air, um, this teenager protein over to the original protein. And so, uh, this distinguishes between de nature ation and Renate aeration, and we'll be able to get some practice in our next practice video, so I'll see you guys there.
Which of the following is likely not affected if the pH of a protein solution is suddenly altered to 12?
Amino acid composition.
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So in our last lesson video, we talked about how protein de nature ation can be caused by several different factors, including the addition of specific re agents. So in this video, we're gonna talk about two specific re agents that could be used to de nature of protein. And those are your area and bottom or Capito ethanol. And so what you'll see is that Yuria is actually known as a kaya tropic agent. And all this really means is that it on Lee disrupts the non Covalin interactions. And so what this means is that it's going to disrupt the non covalin interactions between our groups, and that's going to affect the tertiary structure and D nature, the protein. So it turns out that, uh, Kaya Tropic Agents Scientists don't really fully agree on the mechanism that it really uses, but they do know that these air molecules that ultimately disrupt the hydrogen bonding network of water molecules and we know that in biological systems, the solvent for all of our proteins is going to be water. And so if we disrupt the hydrogen bonding network of water molecules, that's ultimately going to lead to altered protein stability and that's going to disrupt the protein stability because it's going to disrupt the non Covalin interactions. And so with bottom or capital ethanol. On the other hand, which could be abbreviated by the symbol beta m e. This specifically cleaves or breaks the dies sulfide bonds or the die sulfide bridges, which we know are co Vaillant, our group interactions. And so, the way that bottom or capital ethanol cleaves these die sulfide bonds is via a redox reaction or an oxidation reduction reaction. And so, in our example below, what we're gonna do is talk about the effects of your reem bottom, a capital ethanol, one protein structure and so on the left hand side of our image. What we have is the effect of Yuria and then on the right. What we have is the effect of Beta Moore Capito ethanol. And so what you'll see is that on the left, what we have is our native protein on the far left here, and this is by native protein. What we mean is it's our normal protein, which has its normal structure, so you can see it has its Alfa Hillis is it's got some beta sheets It's got all of its secondary structures in the correct way, and it also has its dice sulfide bonds, which are in red. And so the dye sulfide bonds are all, uh, Covalin, our group interactions. And so our native protein is gonna have normal biological activity, and it's gonna be performing its job the right way. Now if we go ahead and add Yuria, remember that Yuria is a kaya tropic agent that disrupts Onley. The non Covalin interactions well, if we disrupt the non koval interactions were also disrupting the our group non Koval interactions. And that's going to disrupt our tertiary structure. And we know that that's going to lead to a denatured protein. And that's exactly what we have over here on the right, a denatured protein which notice it does not have its secondary structures anymore. But what you'll see is that it's die sulfide bonds are still completely intact. They have not been affected. So we still have our die sulfide bonds here in red, and so the dye sulfide bonds have been retained. Uh, even though we've added this Yuria now, what's interesting is if we remove the Yuria, so that would be this blue arrow here, and some situations were able to re nature the protein and recall that re nature just means to regain the native protein structure and the native biological activity. And so we'll be able to see examples of the effects of Yuria in our next couple of videos when we talk about the and fence and experiment. Now, if we want to completely destroy or d nature the protein, then we need to disrupt all of its our group interactions. Uh, not just the non Covalin, our group interactions, but also the co Vaillant, our group interactions, which would be the dice sulfide bonds. And so we need to be able to break these dice sulfide bonds that air here in red. And that's exactly where bottom or capital ethanol comes into play. So notice that over here what we have is one Sistine molecule, and we know that the Sistine is linked via this die sulfide bridge, which is in red. And so again, with the addition of Beta Moore Capito ethanol, which is this red era at the top. We know that if we add Beta Moore Capito ethanol, which its structure looks like this What we can do is reduce this die sulfide bridge. And when we reduce the dye sulfide bridge here, we actually cleave or break the dye sulfide bridge. And what that leads is to the formation of two separate Sistine molecules. And so each Sistine we know has a soft hydro group in S H group. And so we've got our to S H groups and noticed that they are completely separate. They're no longer linked together via the dye sulfide bridge. And so that is the effect of Baltimore capital ethanol. Now again, what can happen is if we remove the bottom a capital ethanol under certain conditions, we can re oxidize this, uh, these self hydro groups here and reform this die sulfide bridge. And so we'll be able to see examples of that in the infants and experiment when we get to it shortly and our next couple of videos. And so in our next video, we're gonna be able to get a little bit of practice. So I'll see you guys in that video
Which of the following is least likely to result in protein denaturation?
Changing the [salt].
Disruption of weak interactions by boiling the protein solution.
Exposure to chaotropic agents & detergents (such as urea & SDS).