 Hi! In previous lectures we talked about energy landscapes and lots of interactions in proteins and I'm going to continue on that theme today But take this one step further So in terms of molecules we've looked at individual components of molecules But if we now start thinking of an entire large molecule things get a bit more complicated, right? So there are a bunch of ways this one could move. We have the Bond lengths that I can't really show you here I have the bond angles that I would have to show you by twisting a little bit there and In particular you have these torsions some of which you can move and Others that are pretty tight the one in the middle here. It might not be super visible But these are two amino acids and the one in the middle is a peptide bond and as I already mentioned to you This particular peptide bond. I can't really twist around it. It's a double bond So I can well I can stretch the peptide bond a little bit But it won't really change the global properties of the molecule The phi and psi angles on the other hand around each alpha carbon They if I start to move around the phi angle of the first residue and the psi angle around the first residue and Then similar around the second residue Phi and psi you start to see that because these are changing geometries along the main chain They're gonna have a tremendous impact on the different states of molecule Canada I'll show you this in a slightly different way Maybe we should Have a little picture Bobbe's here for you to see The reason why torsions behave that way well It's one thing that they can behave that way geometrically the reason why they will behave that way in practice Is that their energy barriers are low enough that it will happen in practice But high enough that they won't just keep rotating around They will somehow be stuck in a local energy minimum and that's going to be a recurring theme today There were lots of other interactions that you might want to rehash if you didn't We have all these electrostatic and pandavals interactions that are already hinted would be related to hydrophobic effect Although I didn't say how We have direct electrostatic interactions and again all the bonds torsions and everything in these molecules and And ultimately this will behave how the molecule will move say in a free energy landscape