hello and welcome to learn here with peyote for free with massage trick today we're going to be going over the protein structure which is part of the biological molecules unit in a level biology there are going to be quite a few questions where if this is revision that you're watching it for you can pause and have it go if it's the first time you're learning about the proteins then you can pause and add notes so we're gonna start with a question and linking to what you might have learnt GCSE so what our proteins made up of so amino acids those are the monomers which proteins contain if you've already learned this then pause the video and see if you can remember how to draw the general structure at this stage if you haven't already learnt it here's the structure so we have a central carbon with four different groups coming off so we're gonna split it into those four to help you remember so over here we have the amino group sometimes called the amine group so we've got a nitrogen and two hydrogens we also have a carboxyl group C double bond o and then a hydroxyl group the R group what this indicates is the variable group so there's 20 different options of what could be at this point on the carbon you do not need to know those twenty different options so instead you just have to write the letter R which indicates that's the section which is different for all 20 amino acids the final part is a hydrogen so just remember when you're trying to undo all your amino acids central carbon which makes four bonds and these are four different groups so next question then we have two general amino acids here pause the video and link it to what you've already learned so far monomers and polymers see if you can come up with the name of the reaction for how these might join together to form a dipeptide so here we have it it would be a condensation reaction so that is when you join two monomers together creating a bond and water is eliminated and this is where the water would come from so you have the hydroxyl from the carboxyl group and the hydrogen from the amine group and you do actually need to know the location of where the water is removed from the bonds that is made is called a peptide bond and here we have it the peptide bond is what form when we remove the water so carrying on then with the proteins as polymers that's the first thing just to be aware if you are asked what is a protein it is a polymer and the monomers that they're made up of are amino acids so that's what I'm demonstrating in this diagram here each different kind of circle is a different amino acid there's 20 different amino acids and you have a different sequence of the different 20 in each protein there's four different levels of structure that proteins have so in the first made you have this primary structure that's process to make the secondary that gets processed further to make a tertiary or quaternary structure so we're going to go through exactly what's happening in these different levels of development but just pause at this stage to have a look at the diagram to see just based on the images can you describe the differences that you see okay primary structure first now this would be a one mark question describing what the primary structure is and it is the order of amino acids in a polypeptide chain so this here is a polypeptide chain a polypeptide chain is a chain of amino acids all joined together by several condensation reactions the peptide bond holds each amino acid together in the chain the key part of this definition would be pointing out the order or the sequence because every protein has a different sequence of amino acids and we come back to why that is so important secondly structure so that polypeptide chain gets processed and either gets twisted to make this alpha helix or it can be bent and folded to make what we call a beta pleated sheet so that would be your first mark in describing what the secondary structure of a protein is the second stage in processing so we've gone alpha helix or beta pleated sheets now those structures are held in place by hydrogen bonds so I've just demonstrated here these pink dashed lines the hydrogen bonds which would be holding together the Alpha helix and the beta pleated sheets but you again you need to know the location of these bonds so the hydrogen bonds form between the C double bond o and specifically is the oxygen of that molecule in the carboxyl group and one of the hydrogens in the amino group so that's what I've demonstrated down here so hydrogen bonds form between oxygen hydrogen and it's from the hydrogen in the amine or amino group and the oxygen in the C double bond o part of the carboxylic acid and you'd have several hydrogen bonds forming and that's what provides the strength to hold the protein in its alpha helix and beta pleated sheet sorry structure so this is now a three mark definition three key marks are the protein gets further folded so the second restructure is then folded in on itself in doing that you create this unique 3d shape and finally it's for pointing out what is holding that 3d shape in position and there's even more bonds so the ionic bonds hydrogen bonds and disulfide bonds that would be your three mark definition of what the tertiary structure of a protein is but just the point outs and again again you need to know the location of the bonds this time it forms between the R groups so the ionic and disulfide bonds are located between different amino acids but it's between their R groups and a disulfide bonds dime int 2 so it's a bond that falls between two different sulfur's so you'd only get a disulfide bond if you happen to have amino acids within the polypeptide chain which have a sulfur in their R groups the last level of organization or structure is a quaternary structure and this time is still a unique 3d shape but you have more than one polypeptide chain so I've indicated this by giving them different colors so we've got a polypeptide chain folded up which is yellow perfectly pink blue and green an example of this would be hemoglobin because hemoglobin is made up of four polypeptide chains so you're thinking about our tertiary structure that's going to become really important when you learn about the function of particular proteins say for example enzymes and yet Jesus Cu learns about the idea of proteins and enzymes denaturing what that means is the bonds that are in the tertiary structure which hold it in that unique 3d shape are broken in particular the ionic and hydrogen bonds break and if they break unique 3d shape collapses and I'll start to go back to the secondary structure which you can see here the sorts of conditions that would break those bonds would be if you had too high temperature because excess kinetic energy can cause those bonds to break or if you have too acidic or too alkaline conditions because acidic conditions is an excess of H+ hour Klein is an excess of h- and that will give an imbalance in charge which can again break those bonds now we said when we looked at the primary structure that the sequence of amino acids was the key importance in the definition so the reason for that is the exact sequence of amino acids is what determines where the ionic hydrogen and disulfide bonds form in a tertiary structure and where those bonds form determines the unique 3d shape so if you did have a different sequence these three bonds would form in different locations and you would end up with a different 3d shape and if the 3d shape of a protein changes it will no longer function or it will have a different function so if we use enzymes as one example if one of the amino acids code for is different in the sequence the bonds are in a different location different 3d shape that means the active site will be a different shape and no longer complimentary to the substrate if it was to do with the carrier proteins embedded within the cell surface membrane if those were in our different shape whatever is that they bind with to transport cross a membrane would no longer be complimentary and it wouldn't be able to transport cross membranes so linking to all of this it's gonna throw in a question which will become relevant later on in the a level as well what might cause a change in the amino acid sequence so why might you get one of these amino acids incorrectly coded for so the answer would be mutations so if there was a change in the DNA a mutation that change in DNA sequence might then code for a different amino acid and therefore chroma structure changes so that's it for the protein structure you need to know that the proteins are polymers made up of amino acids you need to know the details about the primary secondary tertiary quaternary structures whenever you have a question about prices make sure you are referring to the bonds and the different levels of structure and the location of those bonds because the bonds are what determine the shape the shape is what determines the function so that's it for learn a double biology with Masaryk for free if you want to go back and look at one of the other biological molecules I'll add the links for you to click on or the biochemical tests video so you can see how to test for a protein