carbohydrate molecules so individual monosaccharides can be modified in a variety of different ways by ourselves now generally speaking why would our ourselves want to modify sugar molecules well by modifying sugar molecules the cells can actually change in all to the properties and the functionalities of sugar molecules and this is crucial in many different processes that take place inside our body one very important process in which we modify sugar molecules is in the process of glucose metabolism as we'll see briefly in just a moment so there are two modifications of sugars that we're going to focus on in this lecture we're going to begin by discussing phosphorylation of sugars and then we're going to move on to great consolation of sugars so whenever our cells actually uptake sugar molecules the first step in the breakdown of glucose in glucose metabolism is to phosphorylate glucose is to basically transform the glucose into glucose 6-phosphate so on the reactant side we have the beta anomer of the cyclic form of glucose so we have carbon one two three four five and six and this is the an americorps bin' and it's the beta anamur because the hydroxyl group on carbon one points in the same direction as this group attached to carbon number five so in the process of a sporulation when we transform glucose into glucose 6-phosphate we essentially add the phosphoric to carbon number six as shown in this diagram now what's the major difference between the glucose and the glucose 6-phosphate well the major difference is the presence of this modified group and this group contains a net negative charge specifically a charge of negative two so compared to this glucose molecule which has a net charge of zero this molecule has a net negative charge and whenever a system in nature contains charge what that means is its energy is higher it's less stable and it's more reactive so essentially by phosphorylating a glucose molecule and transforming it into glucose 6-phosphate our cells increase the reactivity of the glucose molecule and that allows it to basically undergo further processes and ultimately break down and form the ATP energy molecules that our cells use as the major energy source now the second reason why we phosphorylate glucose molecules is to increase the polarity of the glucose molecule so compared to this unmodified glucose the phosphorylated glucose contains a higher charge and so it is more polar and because this molecule is more polar it is much less likely to actually spontaneously leave the cell why well because around the cell we have the cell membrane which consists predominantly of nonpolar lipid molecules and so this highly polar glucose 6-phosphate cannot spontaneously leave the cell because it cannot pass across the nonpolar by layer membrane surrounding the cell so once again the first step in glucose metabolism involves modifying the glucose by adding forespore group onto carbon number 6 now if a sporulation of glucose gives it a net negative charge and transforms it into an and ion and this is done for two reasons the first reason is to prevent the glucose from spontaneously exiting the cell and the second reason is to basically increase its energy make it less stable more reactive so that it can form more linkages it can actually break down and form those ATP molecules now let's move on to the process of glycosylation and before we actually examine what that is let's begin once again with this same beta anamur of glucose so we essentially have the beta d glucose molecule in its cyclic form now even though the cyclic form is more stable and it's going to predominate equilibrium we're still going to form a very tiny amount less than 1% of the open chain of this d glucose molecule and in the open chain we see that we have the aldehyde now what's the big deal about the aldehyde group well from organic chemistry we know that when an aldehyde group is in the presence of some type of oxidizing agent for example a copper ion with the charge of positive 2 that will basically undergo an oxidation reduction reaction so this will basically act as the reducing agent and the c2 the oxidizing agent while that will act as the oxidizing agent and what we'll have is will form a carboxylic acid so the thing about this unmodified Z glucose molecule is that it contains an aldehyde group when the glucose exists in its open chain form and the aldehyde group is reactive when in the presence of oxidizing agents and when that happens one will have some type of oxidizing agent in the presence of the unmodified glucose in its open chain form will transform that glucose into a carboxylic acid and such sugar molecules unmodified sugar molecules that can basically react with oxidizing agents to form the carboxylic acids these are known as reducing sugars because they act as reducing agents now under certain circumstances our cells don't actually want this reaction to take place and what our cells do is they essentially remove that aldehyde group by reacting it in the process we call glycosylation which basically transforms that glucose molecule into a glycoside so what happens is we can basically undergo the process in the presence of alcohol so let's suppose we have the simplest alcohol methanol now under acidic conditions for example in the presence of some type of acid let's say HCl so hydrochloric acid what will happen is the hydrochloric acid will basically protonate this hydroxyl group this will basically depart forming a carbo cation intermediate and then this can act as a nucleophile attacking this carbon either from the top side or bottom side and ultimately we form a mixture of these two molecules these two products and these two products are known as glycosides so this is the methyl beta-d-glucose piranha side and this is the methyl alpha G gluco piranha side and notice the difference between these two molecules is simply the orientation this theory of chemistry of this group attached to carbon number one in the beta case this points in the same direction as this group and the Alpha case it points in the opposite direction of this group here so these two products are animals we have the Alpha and the beta anomer and they're called glycosides now this bond shown red the bond between the anna-marie carbon number one on that glucose molecule and this oxygen that is part of this methanol is known as the old glycosidic bond we call it the old glycosidic bond so basically differentiate from the end like acidic bond that we'll talk about in just a moment so the O simply means the bond is between carbon and oxygen and not between carbon and nitrogen as the case is in the end glycosidic bond now what's the entire point of carrying out this reaction why do ourselves actually want to create these glycosides well by creating the glycosides we essentially remove the hydroxyl group and we basically take we remove the hydroxyl group and we replace it with this a group that came from that methanol alcohol and by replacing it with this group we essentially removed the presence of an aldehyde from the open form and if there is no aldehyde presence in the open chain form then that means when either of these glycosides are in the presence of oxidizing agents for example the cupric acid that we spoke of earlier the seat the Cu 2 plus the copper ion with the two plus charge these will not react in the presence of oxidizing agents and they will not play the role of being the reducing sugars because in the open chain form they do not contain the aldehyde group and so these are known as non reducing sugars because they will not act as reducing agents in the presence of an oxidizing agent so unlike the unmodified Z glucose as we spoke about just a moment ago the glucose glycoside does not react in the presence of oxidizing agents and this is because it cannot be converted into an open chain form with an aldehyde group and such unreactive sugars are known as non reducing sugars so inside our cells under certain cases we want to keep the glucose in its unmodified form because we want to be able to react glucose in some way to basically form a bond but under certain circumstances we want to be able to transform glucose into a glycoside to prevent it from actually reacting with other types of reactive oxidizing agents now another way that we that we can transform the glucose into a glycoside is by reacting with amines and we actually spoke about this type of reaction when we discussed DNA and RNA molecules so when a ribose molecule or a deoxyribose molecule in the case of DNA molecules react with some type of nitrogenous base which is actually an adenine we form a nucleus I so this is what we call a glycoside action with a means reaction so the anna-marie carbon of d-glucose so carbon number one can react in presence of a means to form not an old glycosidic bond but the end glycosidic bond because in this case the bond is between the carbon number 1 and a nitrogen atom so if we take for instance this same glucose molecule that we spoke of earlier the beta-d-glucose pyranose and we reacted in the presence of some type of amine we basically replace the hydroxyl group with the amine group and so now this bond and red is known as the end like acidic bond and we'll see many examples of these types of reactions in the lectures to come so the major point of this lecture II is the fact that sugars can be modified in a variety of different ways and by modifying the sugar molecules our cells can actually control the properties and the reactivities of these sugar molecules