uh today we start chapter two which is uh biological molecules and uh we're going to do 2.2 which is carbohydrates and lipids and in this we're going to study the different structures of carbohydrates which are of course the main one is alpha glucose and beta glucose now if you look at 2.21 in the syllabus it says describe and draw the ring forms of alpha glucose and beta glucose now first of all you must be very clear about the numbering and if you remember your all levels the c6h12 o6 now you must know where all of them are present now you can see here there's a one so one then there's a two and then there's a three and then that's a 4 and then that's a 5 and then that's a 6. so carbon 1 carbon 2 carbon 3 carbon 4 carbon 5 and carbon 6. so c6 the rest of the h and the o's of course you've got to also remember them now the difference between alpha glucose and beta glucose now there's a very easy mnemonic which i have made for you alpha is below alpha is below and beta is above but what is it above it's actually all a story about carbon one it's all about carbon one so in alpha glucose the o h is below please remember we only talk of this so the hydroxyl group is below and in this one in beta glucose it is above so this is what you've got to understand this is the only thing you've got to understand is that in alpha glucose the o h is below in alpha glucose o h is below and in beta glucose the o h is above please pause the video make your own notes and remember things in biology you have to learn a lot of things because a lot of rote learning so your first point of the syllabus is draw the ring forms of alpha and beta glucose then we come to the definitions that we have to talk about like a monomer and a polymer now i think you studied that in chemistry as well monomers are simple molecules and polymer is the same uh simple joined together by usually covalent bonds and then it forms a polymer so monos merge will be glucose and which is repeatedly joined by glycosidic bonds and it forms glycogen so monomer is the simple molecule which is of course joined in maybe hundreds or even thousands and it is then joined to form either glycogen or we can also talk of an example like starch then we come on to the next thing is macromolecule now micro molecules can be they're very very large giant molecules and these are of course we can talk of proteins which are made up of amino acids we'll be talking about that later on in this chapter then polysaccharides which are made up of the two types of glucose which is alpha and beta then nucleic acid which is dna and rna and their basic unit is a nucleotide nucleotide so this is an l and that's a e so nucleotide let's get the spelling right nucleotide so dna and rna are nucleic acids and they would be made up of nucleotides we study that in a later chapter again then we talk of polysaccharides polysaccharides are of course alpha and beta glucose and then large molecules and the examples are glycogen which is made up of alpha glucose starch which is again made up of alpha glucose and cellulose is the one that it has beta glucose so please remember there must be some sort of a mnemonic which you remember and then you can remember that beta glucose is only and only found in cellulose then we talk of monosaccharides now monosaccharides is usually the basic general formula ch2on and disaccharides means die means always two we will study dipeptide so sucrose is a disaccharide made up of glucose and fructose then similarly we study maltose which is made up of two glucose units joined together then we talk of the reducing sugars now the reducing sugars are glucose number one fructose number two and number three maltose now glucose and fructose are monosaccharides while maltose is a disaccharide disaccharide means two so two what are the two what are the two monomers in it number one glucose number two glucose so two glucose units joined together by one fourth glycosidic bond maltose now these three are reducing sugar so they will test positive with benedict solution reducing sugars when you take a sample of reducing sugar and you add benedict solution same volume and you heat in a boiling water bath you will see a color change the blue benedict solution will change to a green or an orange depending upon the concentration of the reducing sugar this page is a sort of a page on which you pause the video and you look at these different uh structures which i've given you i know i've given you a whole lot of them on one page but basically it's glucose and fructose joined to form sucrose now some of you are not very clear what fructose looks like now if you look at this fructose here now the fructose molecule has a very distinct structure and it is also a hexose sugar similarly glucose galactose and fructose all our hexoses and a glucose and a fructose combines to form a sucrose i've also given you the structure of fructose here and for you all to really figure it out that how it is a hexose and how the numbering is different than a glucose numbering so this is what you have got to really understand and spend some time on this page and look at all these structures now sucrose is a non-reducing sugar sucrose is a non-reducing sugar so it is not going to give you a positive test with benedict's reagent now when i say sucrose is a non-reducing sugar i mean it's going to give you a negative test with benetic solution so if you take a sample of sucrose and you add benedict solution same volume and you heat in a water bath and the water bar temperature is 100 degrees celsius and you see that it remains blue now this proves if i said it contains some sort of a sugar and it remains blue that means it is not a reducing sugar but is probably a non-reducing sugar this is another diagram with the sucrose now this just to make you understand the structure of sucrose so it's made up of alpha glucose and a beta fructose and it has a please understand this it has alpha one two glycosidic bond so this is not a one four glycosidic bond which we found in other disaccharides so in sucrose there is a alpha one two glycosidic bond and please remember sucrose is number one it's a disaccharide and number two again it's a non-reducing shoulder now we have to study the uh one four glycosidic bond now the 1 4 glycosidic bond as you can see here this is the one alpha the first carbon and then this is this fourth carbon of the glucose next to it adjacent to it now this is going to result in the removal of a water molecule and when a water molecule is removed that's called condensation so a condensation is going to take place and this is going to be formed which is an alpha 1 4 glycosidic bond so you have to understand why am i saying 1 4 why am i saying 1 4 because it's the one of this glucose and it is the four of this glucose so one four glycosidic bond will be formed between and this of course is a maltose molecule now two words have to be very clear to us number one is condensation in anything in which the water molecule as you can see here this water molecule is exiting so this would be condensation but if i want to break this bond if i want to break the bond in which i'm going to add a water molecule because i'm going to add the water is going to split into the o h and the edge so the water molecule is going to break this and that is called hydrolysis please understand this the two the two totally two different things one is the formation of a water molecule and in this in hydrolysis what we do is addition of water addition of water is you know because the water molecule splits into an h and an o h so that this bond is broken and the uh two glucose units can be separated that's what happens in digestion when you have bread or if you have cereals or if you have potatoes the starch is digested to glucose and the glucose enters the blood and then it can be used by your body cells then we come to the structure of starch now starch is made up of two different one is called amylose and the other is called a myelopectin now mri loss is made up of straight chains so they're only and only one four glycosidic bonds so you can see there's this bond this glycosidic lie 1 4 1 4 glycosidic and then another one will be added to it and another one will be added to it and another one will be added to it and so on and so forth so am i lose is only made up of 1 4 glycosidic bonds now a myelopectin please understand first of all there is the one four glycosidic bonds are present so these are all the one four glycosidic bonds and then somewhere we find that there is a one six glycosidic bond now this is the one which we are going to be talking about so here it is this one so one sixth glycosidic bond now if it has one four a myelopectin has one four and one six so this whole molecule is in a myelopectin because it has one four as well these are the one four bonds this one this one and this one and this one these are all one four glycosidic bonds and these are also one four glycosidic bond but this only the one in green where it starts to branch off just like a tree has branches you see there's a main tree and then there's the branches so this is what you've got to understand is that the main one four is there but then there is a 1 6 glycosidic bond so the 1 6 wherever there is 1 6 now in amilos there is no 1 6 no 1 6 but in a myelopectin there is in a myelopectin there is one four and one six so please understand this that starch is made up of two components so when we talk about potato starch or we talk about rice starch now they have different they have different concentrations of amylose and a myelopath and some have more amylose some have more myelopectin of course that's later on that we study about it and we might give it to you in a question in your paper three now we come to the three polysaccharides that we talk about so myelopectin and amylose these together make up start now both of these of course this is alpha glucose this is also alpha glucose but you can see there is more 1 6 bonds in the glycogen molecule you can see that it has more branching it has more branching as compared to the amylopectin but please remember amylopectin is just one part of the starch molecule starch is made up of the branched portion and the unbranched portion you see this amylose is unbranched ami lose does not have any branching so we call this unbranched and a myelopectin we call this branched but in glycogen there is no unbranched portion it's all branched and the branching is much more than what we found in the starch so glycogen does not have any such component there is no such part in which it is not branch this is you see amylose is not branch is unbranched but the myelopectin and amylose plus a myelopectin is starch while glycogen is on its own it's all got one four and one six bonds so glycogen has one four and one six bonds starch has a part which is only one four which is amylose and a part which has 1 4 and 1 6. so please read the question when you are answering this very important part of the syllabus now the last molecule that we study in polysaccharides is cellulose and i told you cellulose is made up of beta glucose but it's a very interesting structure which it has the this is the first one this is a beta glucose and this is a beta glucose but you see this one has flipped 180 degree because you see look at this one look very carefully this 6 is here and this 6 is here so in beta glucose and cellulose 1 6 is above and one six is below so the next one this six will be above and then the next one the six will be below so you've got to be very careful when you are picking up the structure and this is going to be checked in your mcqs whether you understand this or not so in cellulose now you see this is above then this is below then this is above then this is below and then of course it forms it forms these straight chains this is one this is second third because please understand cellulose is a structural polysaccharide so it's only needed for the cell walls and we need it for strength so that cells don't burst and then there are hydrogen bonds between the molecules so you can see the hydrogen bonds between the molecules so these hydrogen bonds hold these together and then this of course forms the micro fibrils and then the fibrils so cellulose is made up of beta glucose and then you can see these it's just like a rope which has many many thin threads joined together to form a very thick rope and then a thicker one so all these cellulose are made up of beta glucose and you see the six carbon flips so it turns it flips 180 degrees and this is something which you need to be very careful about when you're reading the question if they're asking about cellulose you've got to know that this one carbon 6 goes above and then the other carbon 6 goes down now this is a comparison between starch and cellulose now of course this would be am i lows now when you compare it with the one four linkages they're present but then if you look at this this ch2oh is above then this ch2oh is below then this is above and then this is below so that's a very good comparison between am i lose and cellulose this is another comparison between cellulose and amylose and you can see here glucose units rotated 180 degrees relative to the next residue so please pause the video here have a look at this and it says alpha one four link the glucose of course you don't need to know all those details but the beta one for how it flips 180 degrees that is what you have to understand uh this is a very good comparative table and i want you to pause it and have a look at it this is the only one which is beta glucose the rest are all alpha now in this amylose you only have one four but in cellulose also you have only one four so that's a very nice comparative between cellulose and amylose but then am i lows and a myelopectin all this is all starch is made up of my lows and a myelopathy just like a burger has a bun and a patty so similarly starch is made up of amylose and amylopectin so there are two two parts to it so starch is made up of two different structures one is amylose and the other is a myelopectin please understand this because we will be talking about this in the mcqs this last table again is as a comparison it's a good table to go through when you're revising so it's compares glycogen and starch and you can make your notes about it and where one four is printed where one six is present so in mi lows there is no one six something very important that you need to remember that will be all for carbohydrates and another video we'll continue with the lipids and the proteins thank you