hi yeah 12 this is mr lim here again and this is our what's this the sixth video on proteins about the quaternary structure of proteins okay so we're going to be learning about the quaternary structure so what's a quaternary structure it's when multiple proteins can be combined into one larger complex protein and held together by various interactions just like tertiary structures okay so let's say i have protein a if it combines with protein b to make that particular shape okay that will mean that it is a quaternary structure because it's got multiple proteins um making that shape okay and then all the tertiary uh the interactions would be like the um hydrogen bonding the ionic interactions the dipole dipole that kind of stuff would be occurring there to hold those two proteins together all right the difference between quaternary structures and tertiary structures is that the interaction exists between two proteins rather than two amino acids on the same protein okay so hydrogen bonding can hold these things together but this hydrogen bonding can be in both the secondary structure which is between the peptide links it can be in the tertiary structure which can be between side chains of amino acids on the same protein and it can even be in the quaternary structure because it within the side chains of the amino acids on two separate proteins okay so just trying to keep that all inside your head that these interactions exist on different levels right but they're all the same type of interactions they're just on different levels okay um so yeah diagram of quaternary structures and test restructure so that's the quaternary structure there in the red all right but within one protein so say that that green protein um that's just you know a whole bunch of squiggly bits folded up together all right and the hydrogen bonds might be between there and there there and there and maybe there and there okay so those hydrogen bonds hold the protein structure together within one protein and so it's all the same length of amino acids but then when you get between two amino acids oh sorry two lengths of proteins then it's quaternary structure okay so for this to a curve proteins must have complementary shapes which allow enough of the proteins to come close enough to each other to form multiple interactions that can be held together all right and so what that means is that these things aren't like beautiful kind of um they're not beautiful squares and stuff like that so what happens is that these have to be complementary shapes which means that this has to be just like that shape okay and if it's not exactly that shape then these interactions because they have because remember you know these are at the atomic level these interactions won't form if they're not exactly the the same shape even if you have like you know here's that same thing again i don't know and even if you're off by a little bit okay it's like yep even if you're off by a little bit right that means there's interactions here there's interactions here but there's no interactions in the middle these two things are just going to fly apart because there's not enough interactions to hold them together all right um often two of the same protein can fit together to make a larger more complex protein so say like you have um this is one protein protein number one but you have the exact same shape protein number two and the exact same shape protein number three they can all fit together even though they are the same protein they'll join together to form uh one more complex protein where these quaternary interactions uh hold together okay and so the the quaternary interactions are exactly the same as the um tertiary interactions which will be instead except for this the the disulfide links actually i'm not even sure maybe those are there as well but they're all the same but that's the idea that they hold together between two proteins and then make a larger complex protein all right that's it