Membrane Structure 2

As we already said, proteins actually make up a majority portion of the membrane, and they're actually six different types that you confined or six classifications, if you will. You don't actually need to know what each type is and what it's all about. You just need to know that there are six types. Generally speaking, membrane proteins tend tohave a few different functions. They'll act as receptors and signaling pathways. They'll act as channels, gates and pumps to transport molecules across the membrane. And they'll act as enzymes, generally speaking to catalyze lipid bio synthesis and to catalyze ATP synthesis. Now, the exterior amino acids, as in the amino acids on the exterior portion of a protein, tend to be polar and may have carbohydrates attached to them. So these are the portions of the protein that interact with the acquis environment that you see here, so these tend to be polar amino acids. Now the interior amino acids, or amino acids that air inside the membrane in the protein tend to be non polar. So that's going to be like these. I mean, no assets this portion right here in purple. These just gonna jump out of the image here, these air, generally speaking, going to be non polar. Now it's worth noting that this polarity trend actually extends to, uh, the individual Alfa Hillis. Ease of a protein, too. So just for a moment here pretend that we're looking, uh, like a bird's eye view down onto the surface of a cell at a particular protein channel, and it's it's made up of, or a particular protein. Let's just say and let's say that it's made up of, like, six Alfa. He'll OSI's and I'm sorry my drawing isn't perfect. But say these six Alfa he'll seize come together to make a particular protein. And what I mean to say that Alfa he leases have a polar in a non polar side is these exterior portions that I'm kind of highlighting in blue. Those portions of the Alfa Helix are going to you interact with the membrane, right? That's what they're touching, their touching the membrane. So those air gonna tend to be non polar amino acids, whereas the amino acids on the interior portions of these chains that I'm highlighting in red those air gonna be polar amino acids and remember that each one of these is an Alfa Helix, so and we're looking at it on a top down level. So, um, that means that if you were to think of the primary structure of this alfa helix and go amino acid amino acid, you'd be alternating every few amino acids between polar and non polar amino acids. So I'd be like two non polar than two polar than to non polar than two Polar. Something like that, it wouldn't actually necessarily work out. Like I said right there. I'm just trying to sort of illustrate the point. Uh, now, it's also important to note that Foss Philip IDs that is membrane possible lipids can be associated with the interior portions of proteins as well as the exterior surfaces. So, of course, in an embedded protein, um, these portions, for example, what we see in dark blue here, those portions air gonna be associate ID with the interior portion of the membrane, and therefore they're going to be associated with foster lipids, right? They're gonna have hydrophobic interactions, uh, kind of holding them together. But thes interior portions that we see in light blue Those interior portions of the protein are also potentially can be associated with membrane boss Philip. It's that is to say, membrane faucet lipids can get into the insides of these proteins as well. Now, how do we know what part of the protein is going to be associated with the interior segment of the membrane and what parts of the protein are going to interact with the acquis environment that surrounds the membrane? Well, we use something called hydro pithy Index to reveal what the hydrophobic and hydro filic portions of the membrane are again. That's a hydro pithy index. You can see an example of one right here. Basically, the way this works is, um, amino acids in a protein are given like a sort of, uh, hi drop with the rating, and it's either positive or negative number. And, um, that value dictates whether it's hydrophobic or hydro. Felix so positive values our hydrophobic, whereas negative values are hydro filic, and you can see that we basically scan along the poly peptide and some regions like this our hydrophobic or they have a hydrophobic ratings, so they're probably internal because they're made up of mostly hydrophobic amino acids, so they're probably going to exist in the hydrophobic internal environment of the membrane, whereas thes portions that have a negative value are more likely to be external because they're Mawr hydro Felix. So they're more likely to associate with the acquis environment. So you don't really need to know how. Thio, How toe, You know, precisely, read a hydra apathy index. You just need to have a general understanding of what it's showing. And just to be clear, these, um, thes green markings on the image are showing the different regions of the protein and where it crosses through the membrane. You don't actually need to worry about any of that. You just need to know what the general values mean. Negative is hydro filic. Positive is hydrophobic. Positive tends to be internal. Negative tends to be external now, couple of things to note before we move on. Trip to fan entire scene. Boy, those guys always show up together, right? They always are appearing together because they have similar properties, obviously, and it turns out that they tend to be found right at the edge of the membrane and trans membrane proteins. So if we go back up to this image here we see these trans on all the way in the left, these two proteins here, these air trans membrane proteins and basically, ah, tyrosine and trip to fan. We would tend to find right at the edge of the membrane, like where I'm marking in red here so the you're most likely to find tyrosine trip to fan in a location like that. Also worth noting is that peripheral proteins are always attached to a fatty acid that's embedded in the memory, and we can see an example of this right here. Where we have this fatty acid and attached to it. Is this peripheral protein all right with that? Let's flip the page.