If you haven't done question 27 yet, pause the video now. Hopefully, from the question on the previous page, you'll know that the answer is B because there is no phospholipase B1. You have A1, A2, C, and D. And the reason there is no B is that B was actually renamed A2. Now, question 28 is also quite similar to the one we saw on the previous page. So hopefully, this one will be a breeze for you to solve. You do 25750, and 7580000. And that gives you 0.3 repeating and 0.0009375. Divide those two numbers and you get 35. A hydropathy plot is used to predict whether a given protein sequence contains membrane-spanning segments. A hydropathy plot is a graph that looks like this. Here's your zero-point. Here is your negative region and your positive region of the graph. And you are going to have this line like this that goes back and forth between the different regions. And basically, the positive region is representing what is hydrophobic, the hydrophobic segments. The negative region is representing the hydrophilic segments. What you more or less want to do is you're looking again, remember, 20 amino acids is the minimum amount to span the membrane. So you're looking for a window of about 20 amino acids in the hydrophobic region. And, you can use, like, 7 to 20, but let's just say 20. And when you find something that fits the bill like that, like this for example on our mock graph here, and say, Oh, that's a membrane-spanning segment. Alright. That's basically all there is to it.
The fluidity of a lipid bilayer is increased by, increasing the temperature. Decreasing the number of unsaturated fatty acids would decrease fluidity. Unsaturated fatty acids increase membrane fluidity because they have lower melting points. Obviously, decreasing temperature, that's the opposite of what is true. Fluidity fluctuates with temperature increases. And increasing the length of the alkyl chains will actually decrease fluidity because, if you recall, from lipids, the longer it is, the higher the melting point. So, shorter chains will have a lower melting point and will therefore make a more fluid membrane. And lastly, substituting an unsaturated fatty acid for a saturated fatty acid will increase the melting point of the unsaturated molecule, which will have a much higher melting point than the saturated molecule. Therefore, putting the unsaturated molecule in will decrease fluidity.
Lastly, peripheral membrane proteins are generally non-covalently bound to membrane lipids. They usually associate via hydrophobic interactions. Peripheral membrane proteins are not usually denatured when released from membranes, because they're not deeply associated with the membrane. They're peripheral to the membrane. They can be released from membranes only by treatment with detergents. No, that's transmembrane proteins. And may have functional units on both sides of the membrane? Absolutely not. They're peripheral. Meaning, they're on one side, right? One side or the other. Not both and penetrate deeply into the lipid bilayer. No. They are very weakly associated with it. Alright. Let's flip the page.
