Hi in this video, we are going to talk about protein folding. So the first there's four levels of protein folding. And the first one that we're going to talk about is the primary structure. So what is the primary structure? The primary structure is the linear sequence of amino acids in a polyp peptide chain. So this is just the order of amino acids. Now this is this is important to know because the R groups of the sequence of amino acids gives the information for folding or otherwise known as the three D. Confirmation of the protein structure. And so the amino acids themselves are attached to be a covalin peptide bonds, which hold the amino acids together to form the primary structure. So if we're just looking at what the primary structure is, you have this linear sequence of amino acids going this way and they're attached through Covalin peptide bonds. And each one of these amino acids has an R group and it gives the protein its unique properties. So let's move on.

So in this video we're gonna talk a lot about the secondary structure of amino acid or the secondary structure of proteins. And the secondary structure refers to the local sort of nearby close structures borne by the polyp peptide backbone. So there are two main ones that we want to focus on. The first is an alpha helix and what an alpha helix is is its hydrogen bonds made between every fourth amino acid. And this allows for this rigid cylinder to form that can either be right handed or left handed. But essentially it's a helix um of proteins that forms in this like rigid cylinder coal structure. And at this type of just so you know, sort of more about it, alpha helix has found a lot of times in skin proteins. Now the second one is the beta sheet and this is hydrogen bonds made between segments of the polyp peptide chain but they're arranged side by side and so they can be parallel where two chains are going in the same direction, or anti parallel with two chains going in opposite directions. Let me scroll up so you can see that. And this type of pattern is abundant in skin proteins. So let's look at the this so we can see what it actually looks like. So here you have your alpha helix. So that's the cylindrical chain made by hydrogen bonds between every fourth amino acid and then you have the beta sheet and these are hydrogen bonds made between um sort of sheets of the poly peptide backbone and these can run parallel or anti parallel. The ones you're seeing here are anti parallel because one is going this direction and one is headed that direction, so that's secondary structure. Let's move on.

So in this video we're going to talk about tertiary structure which is actually referring to the 3D confirmations formed by a single so one polyp peptide chain and these confirmations can be functional or structural and so there's a lot of information behind me, there's a lot of vocabulary and just sort of understanding this. But as we go through all the different levels of protein structure of course they have to get more complicated. So there's a few types of really to kind of structural things that we need to know about when referring to structural or tertiary structure. The first structural motifs and these are two or more secondary structures that work together to form a 3D structure. So for instance one of these is called a coiled coil. So this is 2 to 3 alpha helix sees. So those are the secondary structures we're talking about in this definition. So 2 to 3 alpha helix cities that wrap around each other and form this really stable um motif. And so um so that's an example of one, there's a couple of other that you may read about in your books called the helix turn helix or helix loop helix. And these are named based on, you know how these multiple helix is or how these multiple secondary structures come together to form this three day tertiary structure. And so each structural motif usually has a specific function in the protein. Now the second type of tertiary structure, I want to talk about our protein domains and these are kind of larger segments of the polyp peptide chain around 40-350 Amino assets. And they can fold into independent stable structure. So like the motifs each domain usually has a specific function. Um So you may um read about some of these domains um and they're usually sort of commonly found in multiple proteins. So the same domains can be found in multiple proteins. An example of this would be the S. H. Two domain. Um and it sounded over around 120 poly peptide chains. You don't need to know that domain right now. Just know it's an example of a domain that's found in multiple proteins. And this um This happened because of a process called domain shuffling which occurred throughout evolution to sort of link different protein domains and new combinations and new proteins. So, domain shuffling is the reason that we have all these different domains um sprinkled throughout different proteins. And so domains are extremely important feature of tertiary structure. They are found in two thirds of proteins contain actually more than one protein domains, two plus so protein domains are really important. And so um tertiary structure also forms two main protein types. Fibrous protein and globular proteins, fibers, proteins are proteins with this elongated shape and globular proteins are sort of more globular, they're kind of more of a compact shape. So if we're looking at what is a tertiary structure of a protein look like. Here we go. We have you can see these sort of secondary structures here, the alpha helix, these beta sheets going through out here, but the tertiary structure is how these all work together um in a single poly peptide chain. So you have multiple of these beta sheets, you have multiple alpha helix sees, and these all come together to create specific motifs or specific domains within the protein um that forms this tertiary structure. So let's move on.

So this video we're gonna talk about the fourth protein folding level and that is a co ordinary structure. So this structure refers to a protein complex with more than one polyp peptide chain. So these are multi merrick proteins. Remember Multi merrick means they have more than one poly peptide chain usually with two plus polly peptide chains. And each polyp peptide chain is called a sub unit. So each sub unit can be identical or non identical to other sub units. Remember sub units the polyp peptide chain. So for instance a home a timer is going to be with a protein with two identical subunits and a hetero dime er will be protein with two non identical subunits. And these pa the peptide chains are linked through non violent bonds but they also can be linked to the isil five bonds between this um side of scenes between each probably peptide chain forming really stable um multi merrick proteins. So if we were to look at what this looks like, we have our uh we have four. So this is a multi marriage protein team erIC and we have our four poly peptide chains. That's 123 and four. They're all different colors. And how these um buying together and formed together to create this single protein molecule is referring to cho ordinary structure. So now let's move on

So in this video we're going to focus on kind of a unique aspect of protein structure. And that's actually the unstructured regions. So unstructured regions can also be called disordered regions and they really exist between ordered protein structures or domains. So unstructured regions are usually surrounded by other very ordered um systematic protein regions. And so the unstructured regions really provide flexibility to the protein structure unfolding they have because they they are not really ordered and they're not necessarily folding for anything. They can actually do all these different functional or structural um aspects to them. So one is that they can wrap around target proteins with really high specificity but low affinity. They can scaffold proteins together. And nearly one third of eukaryotic proteins actually have unstructured regions and at least one polyp peptide chain. And actually some of them can be found as the entire um polly peptide chain. And these if the entire polyp peptide chain is this unstructured region usually going to form an aggregate in the side. It's all so for looking at what an unstructured region looks like on a protein you see here that in these these colored regions are kind of structure. They form more complex structure of these beta sheets. But these regions outside were sort of, you know, outside of these ordered regions are the unstructured regions and they just don't fold into anything and that gives them this flexibility to kind of do whatever the protein needs them to do, They're a really unique structure but a very important one when talking about protein structure unfolding. So now let's move on