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Cell membrane proteins

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Video transcript

in this video we're going to explore membrane proteins did you know that the cell membrane can be composed up to 75% protein so most most cell membranes have about 50% or less protein and proteins are there because the cell membrane uses proteins for pretty much everything that it does all of these cell membrane processes that it performs so just to remind us what a cell membrane actually is a cell membrane is made up of little things that look like this which are called phospholipids and they come together and form what we call a lipid bilayer so over here I've pre-drawn a lipid bilayer and it'll look something like this it'll be made up of a lot of these small phospholipids that we've drawn above and it'll make up our bilayer so you can see that there are two layers of these phospholipids now there's two major types of proteins in the cell membrane the first can look something like this and this can appear anywhere in the cell membrane and they're usually quite a few of these throughout the entire cell so this is what we call an integral protein you'll notice that it's called an integral protein because you can think of it like it's integrated throughout the entire membrane another type of protein that we might encounter might appear on top of the membrane occasionally it might be slightly into the membrane and it can also rest on top of integral proteins and this we call peripheral proteins and the reason why we call it a peripheral protein is because it's on the peripheral or the outside of the cell membrane the difference between peripheral and integral proteins is that integral proteins are really stuck inside the cell membrane as you can see in this picture the integral protein is really inside the membrane and as a result it'll be very difficult to remove peripheral proteins kind of a catch and remove themselves from the cell membrane or from other proteins they generally are therefore different cell processes so for example a hormone might be a peripheral protein and it might attach to the cell make the cell do something and then leave peripheral proteins can also exist inside the cell on the cell membrane another type of protein is extremely rare and it can appear inside the cell membrane like that and we call this a lipid bound protein why might you think a lipid bound protein is so difficult to find so rare well the reason why is because proteins are there to interact with the outside environment and lipid bound proteins are stuck on the interior of the cell membrane itself so it can't really interact with the outside of the cell or the inside of the cell so it doesn't really serve a big function in terms of the cell membrane performing its duties we're going to spend a little bit of time talking about two types of integral proteins that are extremely important because these two proteins are found all over the cell and they help the cell maintain homeostasis or balance the first type can look something like this again this is an integral protein what do you think this protein might be used for this isn't two proteins it's actually one protein with a hole through it well this protein is actually used to allow things to pass through the cell we call this a channel protein and like the name kind of implies there's a channel or hole inside the protein that lets things pass through so for example if there is some sort of ion let's say this is an na plus ion a sodium ion this is outside the cell and the cell at this point really needs these sodium ions to perform a really important process so what the channel proteins do is they'll allow these outside extracellular ions into the cell and normally these sodium ions wouldn't be able to pass through the cell membrane by themselves these channel proteins allow our bodies to take in different materials from the outside environment into ourselves what they can also do is they can also do the reverse so let's say your cell has way too much sodium and it needs to get rid of it so channel proteins can start pumping these out channel proteins generally don't require energy so there's no energy needed sometimes we call energy ATP and another thing that's special about channel proteins is you'll notice that it'll go with the concentration gradient so out here there's a lot and inside there's very little so it'll pump from where there's a lot of sodium into where there's very little so it'll go what we call down a concentration gradient concentration gradient the second type of very important integral protein is called a carrier protein and like the name implies it carries substances into the cell I kind of picture it like a baseball glove like this so if there's a molecule that's outside the cell and the cell actually needs this molecule so what the carrier protein will do is it'll actually protect this substance so that it can enter the cell safely it can also do this in reverse it can take something inside the cell and pump it outside the cell and this type of protein is really important because unlike channel proteins carrier proteins can go against the concentration gradient and this is really important because say your cell has a lot of chloride ions and your body needs more to perform a certain process so what your body can do is it can bring more chloride ions into yourself even though your cell already has a lot of chloride ions so carrier proteins can sometimes use energy or ATP finally there's a type of protein that can exist on any of these that we've drawn here and this is what we call a glycoprotein so what a glycoprotein would look like is there will be a chain of sugars attached to a protein and it can be on integral proteins peripheral proteins channel proteins glycoproteins you'll notice have the prefix glycol which means sugar and basically it's just sugar plus protein and the purpose of glycoproteins is that it's used in signaling so it allows a cell to recognize another cell so in summary in this picture that we have drawn out of a cell membrane and several different proteins we have two main classes of proteins we have peripheral proteins which are on the outside of the cell and they're really easy to remove we have our integral proteins which are stuck inside the cell and really tough to remove we have our lipid bound proteins we have channel proteins which allow things to move through the cell by its concentration gradient and it doesn't require energy and it doesn't require ATP we have our carrier proteins which are kind of like a baseball glove it can take in a particular molecule and let it out inside the cell or it can do it in reverse and these can sometimes use ATP and what's special is they can go against the concentration gradient and finally we have glycoproteins which really can be any of the proteins that we've drawn out it's a sugar plus a protein and it participates in signaling so cells can recognize each other