Integral Membrane Proteins - Video Tutorials & Practice Problems
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Integral Membrane Proteins
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Video transcript
In this video we're going to talk even more details about integral membrane proteins. And so recall that we already introduced integral membrane proteins in our previous lesson videos. And so we already know that integral membrane proteins are integrated into the membrane as we can see down below. And so these are membrane embedded proteins. Now, because integral membrane proteins are integrated into the membrane, they are pretty firmly anchored to the membrane, which means that they are tightly associated with the membrane, and this is because they form lots and lots and lots of And so And so these integral membrane proteins are so tightly associated with the membrane that if we wanted to isolate an integral membrane protein from the membrane, we would first have to disrupt the structure of the membrane using a detergent, and then after we disrupt the structure of the membrane we could then isolate the integral membrane protein. And so that just goes to show that these integral membrane proteins are really tightly associated with the membrane. Now the hydrophobic environment within the membranes actually stabilize alpha helix structures. And so the alpha helix is actually the most prevalent secondary structure in integral membrane proteins. And so whenever you see an integral membrane protein, the likelihood is that it's go probably going to contain an alpha helix structure. And so what you'll notice is looking down below at our image over here on the left, notice we're showing you 2 integral membrane proteins, glycolforin over here on the left, and rhodopsin rhodopsin over here on the right. And notice that they both form lots and lots of alpha helix structures within the hydrophobic environment, which is going to again stabilize the Alpha Helix Structure. Now, integral membrane proteins contain at least one Transmembrane Spanning Domain. And so the Transmembrane Spanning Domain, again, generally includes an Alpha Helix Structure. And so notice that Glycophoran over here on the left, has one alpha helix, and so therefore it has one transmembrane spanning domain. But then notice over here on the right hand side, rhodopsin actually has a total of 7 alpha helices that we're labeling here. And so because it has these 7 alpha helices, it also has 7 transmembrane Spanning Domains. Now, if there are multiple Transmembrane Spanning Domains, they're typically connected by loops at the membrane surface. And so notice that the alpha helices here are connected by these loops that we see, at the surface of the membrane. And so that's another important idea to note. Now, over here on the right hand side, we're reminding you guys of how proteins tend to fold, depending on the environment that the proteins are in. And so in polar aqueous environments, proteins will fold in such a way where the polar amino acids are on the perimeter so that they can interact with the polar aqueous environment and the non polar amino acids would fold into the interior of their protein because they are hydrophobic. However, what's important to note is that in the opposite environment, in a hydrophobic environment within a membrane like this one over here on the right hand side, notice that the protein folds in the opposite way. Notice that on the perimeter of the protein this time, the non polar amino acids are gonna be on the perimeter and the polar amino acids are going to be on the interior. And again, this is going to be occurring on, the inside of the membrane in that hydrophobic environment. And so that's an important idea to keep in mind about protein folding. And so, this here concludes our introduction to integral membrane proteins and in our next lesson video, we'll be able to introduce a very specific integral membrane protein. So I'll see you guys there.
2
concept
Integral Membrane Proteins
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3m
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Video transcript
So in our last lesson video we said that the alpha helix is the most common secondary structure in integral membrane proteins. But in this video, we're going to talk about an exception, which is in the integral membrane proteins called porins, which have beta barrel motifs. And so as we just mentioned, porins are just a class of integral membrane proteins that contain a beta barrel motif. And so recall from way back in our previous lesson videos that a motif is just a pattern or a combination of secondary protein structures. And so as the name implies, porens function as pores or channels to allow specific molecules to cross the membrane. Now, this beta barrel motif is really just a combination of anti parallel beta sheets that come together to form a hollow cylinder, and this hollow cylinder has a hydrophilic interior and a hydrophobic exterior, and this specific pattern allows the passage of specific polar molecules to cross the membrane. And so, what's important to note is that these horns are commonly found in bacterial cell membranes, as well as in the membranes of mitochondria and chloroplasts. And so, really, this is not a surprise since we know the endosymbiotic theory suggests that mitochondria and chloroplasts used to be their own bacteria, and so again, not really a surprise that the bacteria, mitochondria and chloroplasts all share this porent integral membrane protein in common. And so if we take a look at our image down below, notice on the far left, we're showing you the Beta Barrel motif, which is again, just a combination of anti parallel beta sheets that form this hollow cylinder. And again, the hollow cylinder has a hydrophilic interior and a hydrophobic exterior. And so when it's embedded in the membrane as we see here, the hydrophobic exterior is able to interact with the hydrophobic membrane. And then of course, the hydrophilic interior allows the passage of specific polar molecules to cross the membrane. And again, over here on the far right, we're just reminding you that these porins are commonly found in the membranes of both mitochondria and chloroplasts, as well as in bacteria. But of course, the mitochondria is going to be more relevant to us. And so this here concludes our introduction to porins and beta barrel motifs and again this is an exception to integral membrane proteins. And we'll be able to get some practice applying the concepts that we've learned in our next couple of videos. So I'll see you guys there.
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Problem
Problem
Which of the following statements about integral proteins is NOT correct?
a) They are firmly associated with the membrane.
b) They contain hydrophobic regions that interact with hydrophobic lipid tails.
c) They can be easily extracted/separated from lipid membranes by just a relatively small change in the pH.
d) They commonly contain α-helices or multi-stranded β-barrels.
A
They are firmly associated with the membrane.
B
They contain hydrophobic regions that interact with hydrophobic lipid tails.
C
They can be easily extracted/separated from lipid membranes by just a relatively small change in the pH.
D
They commonly contain α-helices or multi-stranded β-barrels.
4
Problem
Problem
Integral membrane proteins are proteins that:
a) Loosely associate with the membrane.
b) Can be released from the membrane by slightly changing the pH.
c) Can be released from the membrane by slightly changing the ionic strength of the solution.
d) Penetrate or span the membrane.
A
Loosely associate with the membrane.
B
Can be released from the membrane by slightly changing the pH.
C
Can be released from the membrane by slightly changing the ionic strength of the solution.
D
Penetrate or span the membrane.
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Problem
Problem
In the hydrophobic environment of a membrane, the α-helix of a protein folds such that the outer surfaces contain mostly _________________ amino acids, while _________________ amino acids are mostly buried on the inside.