hello everyone welcome back in this lecture we're going to begin our review on the first macro molecule out of our four classes and that's the carbohydrates carbohydrates are food source for most organisms and structural material for plants the empirical formula for carbohydrates this general formula consists of carbon and waters so you can see there ch2o n the n represents or indicates the number of carbon hydrate groups and the n can vary from three to well over a thousand for some of the larger polymers the term carbohydrate or sugar encompasses monomers called monosaccharides this literally means one sugar small polymers just a few monosaccharides these are small polymers called oligosaccharides and then we have the very large polymers long chains and these are called polysaccharides these simple sugars differ from each other in three ways one the location of their carbonyl group two the number of carbons and three the spatial arrangement of the atoms for example the position of the hydroxyl group you can see from this slide here the names pentose pentoses two examples of the pentoses are ribose and arabinose and then there's hexoses for example fructose and glucose you can see that they all have this ending that's in common so sugars end with ose there they end in os you can also have a triose what sounds familiar when you hear trios pentose hexose this is reflecting the number of carbons so a triose would be three carbons a pentose would be five carbons and a hexose is a six carbon molecule let's do a quick check on how these names and endings help to remind us of what we're talking about what do enzymes end in what are the three letters at the end of an enzyme write that down in your notebook okay the word carbohydrate or the name carbohydrate is a little misleading because carbohydrates do not consist of carbon atoms bonded to water molecules they are actually made up of your carbonyl group which is the c double bond o and we had two types if you recall we had aldehydes and ketones this is where it's important to see the position of that carbonyl group in this first one here on the left our glyceraldehyde is an aldo triose aldo because it's an um got the carbonyl group on the ends so it's an aldehyde trio stands for trios it's a three carbon sugar one two three carbons so we have our carbonyl group c double bond o with an h it's on the n this tells you that it's an aldehyde specifically this molecule is a glyceraldehyde we also have the oh group these are our hydroxyls and then we can see carbon and hydrogens also are bonded let's apply our generic formula and see if this holds up so we have our ch2 n the n represents our number of carbons so if that number is three if n is equal to three we would have three carbons six hydrogens and three oxygens so let's check and see if our formula holds up well we can see it's a triose there's three carbons there are one two three four five six hydrogens and one two three oxygens so this clearly by the number of carbons the position of our carbonyl group and we have our hydroxyls this would clearly be a sugar you should be able to recognize that this is a sugar over here we have the carbonyl group that's in the middle if you remember this was c double bond o and then you had two r groups in our aldehydes you have a hydrogen and then an r group bonded to the c double bond o and here we can see c double bond o and it's in the middle with an r an r group to each side and again even though the order of your atoms is a little bit different that functional group is in a different position the ch2o to the n remains the same this is a ketone or a keto triose again it's a sugar there are three carbons and it has the carbonyl group in the middle let's take a moment and think about this this is the structure of formaldehyde my question to you please write this in your notebook and write down whether or not this is a sugar and then the key to this is to know why or why not so is formaldehyde a sugar why or why not put that in your notebooks please sugars are fundamental to life they provide chemical energy and they're a source of carbon atoms for building other molecules sugar monomers again are monosaccharides mono being one and some of these examples would be fructose glucose and honey honey is actually this is an image of the structure of honey and they are in single units of glucose and single units of fructose so that's why they're considered a monosaccharide monosaccharides can be hooked together by dehydration reactions to form more complex sugars and polysaccharides here's an image that you can see glucose fructose and galactose these are monomers and in this bottom image you can see that these independent monomers can be linked together by our dehydration reaction to form a longer chain let's do a review question dehydration reactions and there's loss of water so water molecules are being formed how many water molecules would you have from this molecule right here being built how many water molecules would you have by the linking of each of the monomers puzzle recording and please write this down in your notebook the presence of a carbideal group along with multiple polar hydroxyl groups means that even the simplest sugars have many reactive and hydrophilic functional groups based on this observation and what you can see in the images on the slide it should not be surprising to you that sugars are polar molecules that form hydrogen bonds with water and are easily dissolved in aqueous solutions remember like dissolves like you can also see in the image that the spatial arrangement of the atoms is a little bit different the image illustrates that the different structures of two hexose sugars glucose and galactose both of the sugars have terminal carbonyl and the same molecular formula which would be c6h12o6 but they differ in the spatial arrangement of a single hydroxyl group take a moment and see if you can find that difference there's one hydroxyl group that the spatial arrangement is different look at both glucose and galactose and see if you can find that difference this slide just recaps many of the things that we've discussed thus far the carbon skeletons of monosaccharides vary in length glucose and fructose are six carbons long and others have three to seven we're talking about monosaccharides that's what you want to keep in mind monosaccharides are the main fuels for cellular work and are used as raw materials to manufacture other organic molecules in this figure you can see that the monosaccharides appear as linear chains but this is actually rare for sugars containing five or more carbons to exist in this form in an aqueous solution they spontaneously form ring structures when the carbonyl group reacts with a hydroxyl group on another carbon when glucose forms a ring the c1 carbon forms a bond with the oxygen atom of the c5 hydroxyl a hydrogen atom is removed from the c5 hydroxyl and a hydrogen is added to the c1 carbonyl which generates a new hydroxyl group this balanced exchange preserves the number of atoms and hydroxyls between the ring and linear form when the sugar forms a ring structure the position of the newly formed hydroxyl group excuse me will be fixed in one of two possible orientations it will be either below or above the plane of the ring the arrangement of the other hydroxyl groups remains the same the two forms exist in equilibrium the beta glucose and the alpha glucose the beta glucose is more common because it's slightly more stable than the alpha glucose the significance of the two possible forms becomes more obvious or apparent when they are linked together and we will see this in a slide in a little bit so to summarize the distinct monosaccharides exist because so many aspects of their structure are variable we have aldos or ketose and it's the placement of the carb carbonyl group the number of carbons and the different arrangements of hydroxyl groups rings the ring formation of the same molecule also have alternative shapes these variations give each monosaccharide a unique structure and function so let's proceed with how these monomers join together to form polymers when two monomers link together they form what is called a disaccharide here we can see two glucose molecules undergo our dehydration reaction meaning the removal of a water and then they form a link from the carbon one bond of the molecule on the left with the carbon one two 3 4 carbon 4 from the molecule on the right you can see here that the oxygen that's bonded to the carbon 4 on the right is what the carbon one atom bonds to to form this link this is this linkage is called a glycosidic linkage or glycosidic bond two glucose monomers that link together form maltose maltose is a disaccharide so we have one mole one water molecule that was released and we formed a disaccharide called maltose from two glucose monomers you should be able to understand this in a forwards and backwards mode if i said to you you have a disaccharide maltose and a reaction hydrolysis reaction occurs what are your products your products would be two glucose molecules we can watch our dehydration reaction forming our disaccharides notice a water molecule leaving each time that bond is made we can watch it one more time plant spaces so the interesting thing about lactose is a lot of people are lactose intolerant this is because in addition to adding water to this disaccharide to split it into its subunits of galactose and glucose remember that you need an enzyme for every reaction to occur people that are lactose intolerant are missing the enzyme lactase lactase in addition to the addition of the water molecule will split this disaccharide down into its component parts it's breaking the lactose apart now some people are missing this just from even a heritage standpoint but additionally many humans after their teens no longer produce lactase so they may have been able to drink gallons of milk earlier but as you get older uh genetically for some people they stop producing that enzyme and have tummy issues let's now talk about longer chains of sugar units these are our polysaccharides many saccharides these are our macromolecules polymers composed of thousands of monosaccharides polysaccharides can function as a storage molecule or a structural compound the most common polysaccharides found in organisms today are starch glycogen cellulose and chitin another important polysaccharide is something it's a modified polysaccharide and it's called peptidoglycan starch is a polysaccharide composed of glucose monomers and is used by plants for energy storage we do not store our energy as starch we store our energy in a different macromolecule starch consists entirely of alpha glucose joined by glycosidic linkages most of the linkages are between c1 and c4 and the angle of these bonds causes the chain of glucose to coil into a helix what do i mean by the alpha linkage again that's between that's why the oxygen is highlighted in yellow it's between the carbon 1 and the carbon 4. of the adjacent molecules and the oxygen the angulation comes down like this you can see that's different than when you look at the bond here and we'll go over this in a second and cellulose goes upwards in this figure you can see that starch is made up of not just one type of polymer but two types of polymers one is an unbranched molecule called amylose and this contains the only alpha 1 4 glycosidic linkages the image on the right is a branched molecule called amylopectin branching occurs when a glycosidic linkage from the carbon 1 atom and the carbon 6 occurs an amylopectin branching occurs about 1 out of every 30 glucose residues and that's what causes this to branch because instead of the 1 4 linkage what happens is right here you get a bond that occurs between the carbon 1 of this molecule to the carbon 6 of this one glycogen is a highly branched storage polysaccharide in animals and glycogen performs the same role in animals as starch does in plants it's a it is uh energy storage glycogen is stored in the cells of liver and muscle tissues when you start exercising enzymes begin breaking glycogen into glucose monomers and then processed in muscle cells to supply energy here is the glycogen you have these granules that are stored in muscle tissue and liver it's a helical polymer of alpha glucose and is nearly identical to the branched form of starch but instead of the alpha 1 6 glycosidic linkages occurring 1 out of every 30 residues like in starch a branch occurs in about 1 out of every 10 glucose subunits the branches provide more ends for the enzymes to release glucose when your body needs it you'll talk more about glycogen in anatomy and physiology and there's not a whole lot of glycogen that's stored in your muscles maybe about a minute's worth i believe it is and it's just there for emergency because you store your energy in fats right and that's where you get your long-term energy use from but glycogen you don't have time if someone's chasing you or you're in an emergency situation and so your body needs to access that glucose very quickly and so it obtains that glucose energy in an emergency from the muscle tissue and liver all cells are enclosed by a membrane and the cells of many organisms are also surrounded by a protective layer of material called a cell wall polysaccharides are the primary building blocks for most of these cell walls including those in plants fungi and bacteria in plants the major component of the cell wall is cellulose and cellulose is a polymer made from beta glucose monomers joined by beta 1 4 glycosidic linkages the geometry of the linkages such that each glucose residue in the chain is flipped in relation to the adjacent residue again the oxygen is highlighted in yellow and you can see how each adjacent molecule is linked in a flipped orientation this flipped orientation is important because one it generates a linear molecule not the helix that we see in starch and two it permits multiple hydrogen bonding to form between adjacent parallel strands of cellulose and you can see that here in this image as a result your cellulose forms strong fibers consisting of multiple parallel strands joined by these hydrogen bonds the interacting cellulose fibers give plant cells structural support so trying to run into a tree is not going to feel so good right that's the cellulose giving it the strong structure chitin is a polysaccharide that stiffens the cell walls of fungi it's also found in a few types of protists and in many animals for example it's the component of the external skeleton of insects and crunch stations it's what gives it that crunch when you step on a bug so chitin is similar to cellulose but instead of consisting of glucose residues the monosaccharide involved is called n-acetylglucosamine it's abbreviated as nag these nag monomers are joined by beta 1 4 glycosidic linkages and as in cellulose the geometry of the bonds results in every other residue being flipped over in orientation the nag subunits in chitin also form hydrogen bonds between the adjacent strands to produce a stiff protective armor i also wanted to mention peptidoglycan it's a structural polysaccharide in bacteria most bacteria like all plants and fungi have cell walls the primary structural component of bacterial cell walls consists of a polysaccharide called peptidoglycan peptidoglycan is the most complex of the polysaccharides it has a long backbone formed by nag and a component called nam which is n acetyl muramic acid the nag and name alternate with each other and are linked by beta 1 4 glycosidic linkages there's also a short chain of amino acids that's attached at the c3 carbon of nan these links serve the same purpose as the hydrogen bonds between the parallel strands of cellulose and chitin in cell walls of other organisms as far as we know polysaccharides did not play a significant role in chemical evolution once cellular life evolved these chemicals became enormously important carbohydrates are very important in serving as building blocks for more complex molecules such as our nucleotides that make up rna and dna and again they provide fibrous structural materials they also are used to mark a cell's identity and they store chemical energy you should be able to summarize functions of the macromolecules that we're talking about at the end of each unit this concludes our discussion on carbohydrates in our next recording or lecture we'll be talking about lipids you