Nov 8, 2025
in this video we're going to be discussing polymers and the first of our polymeric macromolecules that's carbohydrates and by the end of this video I want you to be able to differentiate between dehydration and hydrolysis reactions in regards to making or breaking down polymers I want you to be able to identify the monomers of carbohydrate polymers name the covalent bond that connects the monomers of carbohydrate polymers I want you to be able to describe how monosaccharides can differ from one another I want you to identify a few key disaccharides and I want you to be able to describe the key differences between structural and storage polysaccharides
so let's take a moment to discuss the definition of apollomon so here we have a polymer and it's amylose starch and what you notice is that it is made up of repeating units and those units are called monomers in this case the monomer is the monosaccharides glucose and so we're just adding glucose over and over and over and over again that's a polymer theoretically this starch can go on forever right we can keep adding glucose to the end to the end to the end to the end and so we have this very long chain of monomers that can again theoretically go on forever
now the reactions necessary to build a polymer to link a monomer to another to a growing polymer is called a dehydration reaction so here is our growing polymer here is our unlinked monomer and what we're going to use is this dehydration reaction to form a covalent bond between the monomer and the growing polymer and the way that works is we lose an H from the polymer we lose an OHA from the monomer that comes out as h2o dehydration losing water alright that's what that means and then we end up with our covalent bond with the new monomer added so dehydration reactions are the reactions necessary to create polymers to add monomers over and over and over again the opposite reaction is the hydrolysis reaction so if we have a polymer and we want to cut off one of the monomers we use a hydrolysis reaction and in this case we use a molecule of water to break that monomer off hydro water lysis to break hydrolysis now many of the enzymes in your saliva and in your stomach are hydrolytic enzymes that means those are enzymes that catalyze that speed up these hydrolysis reactions the breaking down of polymers
so with that said what I'd like to do is help you study macromolecules there are going to be three important polymers that you're going to learn in the next few days and what I want you to do is I want you to remember memorize what the polymer is what the monomer is so what we're adding over and over and over again and then what's the name of the covalent bond that connects that monomer over and over and over again so we have three polymers carbohydrates which we're going to be learning about now we have proteins and nucleic acids so let's fill in this table here the name of the monomer makes up carbohydrate polymer our monosaccharides saccharides and the covalent bond that connects a mono saccharide to a growing carbohydrate chain or polysaccharide chain is a glycosidic bond right do you know the monomers of proteins probably here I'm a lot amino acids and the covalent bond that links amino acids together is called a peptide bond finally nucleic acids right that's gonna be your DNA and your RNA the monomer monomer of nucleic acids are called nucleotides that's your adenine or guanine cytosine thymine right your A's and GS and C's and T's and the name of the covalent bond that connects nucleotides together is the phosphodiester bond you should be filling out tables like this constantly filling them out remembering else filling them out again and this will be a common way that I suggest that you study in several of the different subjects that we're going to be covering
so let's go back to carbohydrates now there are three general classes of carbohydrates that we are going to discuss monosaccharides those are going to be your monomers of disaccharides putting two of them two monomers together two monosaccharides together so here glucose is a monosaccharide sucrose is a disaccharide and then we have polysaccharides that our carbohydrate polymer right where we have lots and lots of monosaccharides connected to one another in a big long chain okay
monosaccharides let's talk about monosaccharides in some detail first what we see is that it only contains carbons hydrogen's and oxygens in this ratio so for example glucose is c6h12o6 they are these monosaccharides are major nutrients for the cells they are also building blocks for the cells they are oftentimes stored in cells as polysaccharides and even though most commonly in the cell a monosaccharide looks like this it also can exist in a chain form and I want you to to focus on the chain form here so that you can look at it in a critical way without having your eyes glazed over so what a monosaccharide is is nothing more than a chain of carbons okay now that chain can vary in length as we'll see in a moment and in one of those carbons exactly one of those carbons is a carbonyl that double bonded oxygen and all the other carbons have a single hydroxyl group connected to it and then everything else is filled out with hydrogen's and that's it you take a carbon chain add a carbonyl add one hydroxyl group to the other carbons and then fill things out with hydrogen's it is a very easy molecule to think about when you see it in those terms let's think about the way different monosaccharides how monosaccharides can differ from one another and one of the key differences is the nature of that carbonyl now that carbonyl group can be an aldehyde it can exist at the end of the carbon chain in that case we call it an L dose so this is an L dose monosaccharide or that carbonyl can exist somewhere in the middle of the chain and we call that a ketose okay that's a ketone group and so we call this a ketose right now all the other carbons are bounded to a single hydroxyl group and one hydrogen or and they filled out with hydrogen's okay so first way we can distinguish two monosaccharides are they an aldose or are they a ketose next the different monosaccharides will differ in the number of carbons in their carbon chain if it has three we call it a trios if it has five we call it a pentose in it if it has six we call it a hexose and so on and so forth so that's another way that monosaccharides can be different from one another and finally they can differ in how the atoms are arranged around the carbons how the different groups are arranged around the carbon so if we have this molecule here where it's both 1 2 3 4 5 6 so both of these are hexoses both of them are aldoses and yet there's still different molecules because look around this carbon here they are different the hydroxyl group here is on the right side where here it's on the left side it might sound like a very subtle difference but it's enough to give them differing chemical properties and be able to maybe interact with enzymes or other molecules differently so although it so looks like a subtle difference it plays a big role in the nature of those molecules the last difference that we may see between monosaccharides is how they form a ring now like I said most of the time monosaccharides exist like this and solution in the ring form and not the chain form this is the reaction this is how a chain form of a monosaccharide goes into the ring form and the way it works it's one of the hydroxyl groups is going to form a covalent bond with the carbon of the carbonyl so this oxygen is going to covalently bond to this carbon and when it does so we lose this hydrogen and this carbonyl becomes a new hydroxyl group so what we get here is see this blue oxygen that's this one here and see this carbon that's this one here so now we have a hydroxyl group and a hydrogen there okay now the way this works is sometimes the molecule can bend this way to attack that carbon or it can bend the there way to attack that carbon and depending upon which route it it goes to become in the ring form will determine the type of anamur it is okay so for example if it goes into the chain form in one way they hi resulting new hydroxyl group will be on the opposite side of the Ring as that c6 carbon the carbon outside of the Ring and we call that the Alpha anamur or alpha glucose in this particular case if it happens in such a way where that new hydroxyl group that's formed is on the same side of the Ring as that sixth carbon we call this beta glucose or the beta anamur of the glucose so again this looks like really a very subtle difference where that hydroxyl group is either up top here or down below here and yet it has an extremely important effect on the structure and therefore function of the molecule that they are involved in
so for example if we add together a whole bunch of glucose molecules to make a molecule of starch a polysaccharide where all of those glucoses are alpha an immerse and we have starch and now starch is is great like we can eat starch we have enzymes that can digest that starch into the different glucose molecules and we can get energy from it however if all of those glucose molecules that make up this polysaccharide are the ada an immerse and instead of having starch we have cellulose and cellulose we don't have the enzymes to break them down so you can eat for example all this cellulose so like all the plant material and the plant cell walls are all made out of cellulose and we simply cannot break that cellulose down that is insoluble fiber it's helpful to clean us out but it's not going to provide any energy for us so an immerse look subtly different but they have very big consequences in the structure and function of the molecules they are involved in
alright so make sure that you go back and you review all the different ways that two monosaccharides can be different from one another and now we go into disaccharides which is nothing more than two monosaccharides connected to one another and they connect to form what's called a glycosidic linkage the way that works is it's always between the this carbon here okay this carbon here is the carbon that got attacked by the oxygen in forming the ring okay this used to be that carbonyl carbon that is all is going to be covalently bound to some of one of the oxygens in one of these hydroxyl groups okay that's always going to be the case it is a dehydration reaction so we get rid of a molecule of water and then we end up with this glycosidic bond now there's some very common disaccharides that you might be familiar with two glucose molecules give you maltose that's the disaccharide that's the sugar that gives that unique flavor to a whopper those malt balls glucose and fructose give you a sucrose that's table sugar and glucose and galactose that makes up lactose that's the milk sugar right some of you may or many of you in fact are probably lactose intolerant you do not have you do not produce the enzyme anymore that digests lactose it instead gets digested by bacteria within your gut producing gas and it it can be uncomfortable okay
polysaccharides now are sort of like disaccharides taken to the extreme it's adding those monomers adding those monosaccharides over and over and over again so you've got hundreds or thousands of monosaccharides that are bound together sometimes they can be the same monosaccharide over and over and over again sometimes they can be different monosaccharides they can be linear or they can be branched now I don't have it on this image here but this is a linear chain what might happen is that we might get another chain going off one of the hydroxyl groups in another direction we'll see an example of that in a moment and they could be made up of alpha animus or beta animus of the monomers of the monosaccharides all right
let's take a look at storage polysaccharides that's our our starch and our glycogen now these storage polysaccharides they're always chains of glucose molecules those glucose molecules are always in their alpha and Emeric state okay in plants these polysaccharides are starch so here we have starch we have two types we've got amylose we've got amylopectin notice amylopectin has this branching here the starch that you find is here in the endosperm of a a wheat a grain of wheat so we have the brand that's going to be the protective layer we've got the germ there's the little baby plant and then we have the endosperm that is primarily starch and what it is it's a fuel source for this growing little baby before it develops the ability to have photosynthesis to perform photosynthesis but what we do right is we grab all these wheat kernels we get rid of that germ we get rid of that brand we grind up that endosperm and lo and behold we've got flour so flour it's pretty much 100% starch now glycogen is how animals store glucose molecules and when you take a look at glycogen that are stored oftentimes or within granules within the cell they look like this they look actually much more similar to amylopectin and amylose it's got a lot of branching
now that is in contrast to structural polysaccharides now structural polysaccharides still consist mainly of glucose monosaccharides connected over and over and over again but the difference here and this is key is that they are the beta anomers of glucose and because of this slightly different structure what happens is the different chains of polysaccharides because they are in the beta anomers they have the ability to form hydrogen bonding with each other very tight so they form these these fibrils and that means that they're in soluble in water right if you take starch and you slap it into water it's going to dissolve if you take cellulose and you put it into water you're not going to get it to dissolve cellulose is the main component of cell walls of plants so if you take a look at hay for example out there being a bale of hay here it's pretty much 100% cellulose your t-shirt pretty much 100% cotton cellulose chitin is another type of structural polysaccharide that's responsible for the integrity of the exoskeleton of insects and fungal cell walls and both of these involve monomers so glucose monomers that are in the beta anamur and that's why they have these unique properties they won't dissolve in water and they're very tough
so again make sure you go through this video several times take notes be ready to ask questions and be able to do each one of these learning objectives