Overview of Glycolysis

in the previous several lectures we discuss the details of the three stages of glycolysis so now let's actually put all that information together into a single lecture to actually try to make sense of things and let's summarize our results so glycolysis is the breakdown of glucose into pyruvate molecules ATP molecules and NADH molecules and all this takes place in the cytoplasm of the cell now we typically break down glycolysis into three stages we have stage 1 that consists of 3 steps we have staged 2 that consists of 2 steps and we have the most complex stage stage 3 that consists of five steps now the reason we break down glycolysis into these three stages is because each one of these stages actually carries out its own specific purpose it has its own specific purpose it carries out a specific function so let's begin with stage one in stage one the entire point of stage one is to take that glucose molecule trap that glucose molecule inside the cell so that it can't actually leave that cell and begin preparing that glucose molecule for cleavage which takes place in stage two so the entire point of stage 1 is to prepare that molecule for stage 2 where it basically is cleaved into two identical 3 carbon molecules and once it is cleaved in stage 2 it's the third stage where we harvest some of that energy we capture some of that energy to form ATP molecules as we'll see in just a moment so as we discuss each one of these individual processes keep that in mind because ultimately for instance in stage one each one of these reactions takes place and each one of these reactions essentially wants to accomplish that end goal so each one of these reactions in stage 1 once the wants the trap that molecule in the cell and wants to destabilize the molecule make it more reactive so that event it is prepared for stage two to break down into smaller molecules so let's begin with stage one process one step one so our glucose makes its way into the cytoplasm of the cell what happens is an enzyme known as hexokinase hexyl means we have one two three four five six carbons in our sugar kinase means we're going to phosphorylate that glucose so a force for group is taken from the ATP by the hexokinase and is added onto carbon number six and so we form glucose 6-phosphate we break down the ATP into ADP and also the H ion is released as well and this reaction releases this amount of energy so it's an exergonic reaction that's because the ATP is broken down into a more stable molecule and that drives this exergonic reaction now the point of this step is to one destabilize the glucose to make it more reactive and begin preparing it for stage two and the second point is by adding this polar component we trap that glucose in a cell it will not be able to exit that cell because one it can't pass the membrane and B it cannot use any of those transport membrane proteins because its structure is different now let's move on to step two in step two the goal is to basically take that glucose 6-phosphate and transform it into an isomer into fructose 6-phosphate why well because in stage two we basically want to produce two identical three carbon molecules and to produce those two identical 3 carbon molecules we have to have symmetry in our molecule so this is not symmetric but this is symmetric and so the glucose 6-phosphate is transformed into fructose 6-phosphate to make sure we get those two identical 3 carbon molecules in stage 2 so you might ask well if I keep this molecule the glucose 6-phosphate stage what will happen in stage 2 well if we keep it in the glucose that in stage 2 are going to form one molecule that has two carbons and one molecule that has four carbons and that is not symmetric so that's why we carry out step two again the entire goal in stage one is to prepare that glucose for cleavage which happens in stage two and the enzyme that catalyzes this well this is an isomerization reaction we transform one isomer into another and this molecule is a glucose that contains a phosphate and so phosphoglucomutase place spontaneously under physiological conditions let's look at step three so the point of step three is to continue destabilizing that molecule so in step one we destabilize it increased it energy increased its energy and made it more reactive because we made it more polar we added a charge and here we add a second charge and that makes it even more reactive and more likely to actually undergo cleavage in stage two so we take the fructose 6-phosphate and again because we want to add up the spoil root what type of enzyme are we going to have well a kinase what type of kinase well what type of molecule isness it's a fructose that contains a phosphate so phosphofructokinase phosphorylates this process and adds that was for oh group onto this oxygen and now we have a symmetrical molecule and once the cleavage takes place in stage two that will ultimately allow us to produce two three carbon molecules and notice this stage one because we're essentially investing to prepare that molecule for cleavage we actually use energy molecules we use one two ATP molecules in stage one that's why we call this then vestment stage now stage two we call the cleavage state because this is where we break down this molecule that we form in stage one so we take the fructose 1 6 bisphosphate and under the guidance of an enzyme called aldolase why aldolase well because this is an aldol reaction and in fact going backwards is an aldol condensation and so that's why we call this an aldolase so essentially what the aldolase does is it Cleaves the bond here and it forms these two three carbon molecules so again the entire point of this step was to basically create the isomer so that once this process takes place we produce two or three carbon molecules and not a two carbon and a four carbon molecule so we have two three carbon molecules one of them is DHAP which stands for dihydroxyacetone phosphate and the other one is g8p which stands for glyceraldehyde 3-phosphate now this molecule is the one that will go on to stage three so once we form this gap it doesn't do anything else but the DHAP doesn't lie directly on the path of glycolysis and so what we have to do is we have to take this molecule and we have to transform it into this molecule now just like glucose is an isomer to fructose DHAP is an isomer to GAAP because both of these are trioses and a triose is a three carbon sugar so we have one two three carbons one two three carbons both of these are trioses so again we have to depend on an enzyme called isomerase what type of isomerase will triose phosphate isomerase trials because these are tri OSIS and they contain phosphate groups one each and so triose phosphate isomerase basically converts this GH a P the dihydroxyacetone phosphate into the glyceraldehyde 3-phosphate and one stage two takes place we essentially took so the net result of stage two is we took the fructose 1 6 bisphosphate and we cleaned it into two identical 3 carbon molecules these gap molecules so let's move on to stage 3 so essentially in this stage I've only listed the reactions for a single gaap molecule but you should know that all these steps actually take place twice because we have these two molecules that perform in stage 2 so let's move on to stage 3 so remember this is our investment stage we invest energy to prepare it for the cleavage once we cleave it we basically go on to stage 3 and this is where this is where we're actually going to produce those ATP molecules and pyruvate molecules so the entire goal here is to basically destabilize the molecule and eventually create a molecule that contains a high potential to transfer force for groups and we'll see why that's important just the moment so let's take a look at step 6 so in step 6 what we basically want to do is we want to transform the gap molecule into 1 3 BPG why well because we want to transform a molecule that has a relatively low potential to transfer post-oil to molecule that has a relatively high potential to transfer that force oil group and so we basically take the gap we mix it with our NAD+ and we also use a north of us an ortho phosphate and in the presence of gap dehydrogenase so dehydrogenase basically means we're going to have a reaction in which there will be a transfer of a hydride group and so this will be reduced into NADH we're going to release an H ion and that phosphate the orthophosphate will basically attack this molecule and by onto this carbon here and so now we have these two phosphate groups on this molecule so on the first position and the third position and that's why this molecule is essentially a molecule that has a higher potential to actually transfer that was Forel group and so now in the next step we can use 1 3 BPG this same molecule to basically transfer that force 4 group onto an ADP molecule thereby producing an ATP and the molecule that catalyzes this well again it must be a kinase why well because this is a phosphorylation reaction and so we use our phosphoglycerate kinase phosphoglycerate because this is a 1 3 bisphosphoglycerate so we mix it with the ADP because this will accept this group here and so once the process takes place we essentially form an ATP molecule only for a 3 phosphoglycerate now what happens with a 3 phosphoglycerate well in the next step in step 8 we basically want to transform the 3 phosphoglycerate into a into a less stable molecule so we want to take this and destabilize it and that will make it more reactive so that in step 9 it can actually react so to destabilize this the goal is we want to take this phosphate and bring in closer to this negative charge so we have a negative charge of negative 1 and a charge of negative 2 and if we basically decrease the distance between the negative charge that will destabilize this molecule and so we have an enzyme known as phosphoglycerate mutase a mutase is simply an enzyme that takes a group on the molecule and changes its position and so we have the phosphoglycerates of phosphoglycerate mutase will be the enzyme that will take this group and bring it on to the second carbon and so now we have not 3 phosphoglycerate but a 2 phosphoglycerate and notice this is an endergonic process so under physiologic conditions it will not be spontaneous we have to input energy and so this molecule will be less stable than this molecule now so now that we have this less stable molecule we can basically react it in step nine and we can transform it into a molecule that prepares it to form that pyruvate so we take this molecule and we use enolase to transform it into an enol so we have phosphoenolpyruvate or PEP we essentially form a double bond between these and the h and the Oh H combines and a water is kicked off and so this is a dehydration reaction once we form this molecule this molecule is not very stable and it has a very high force for transfer potential why well because this is essentially trapped in the enol state and it's trapped because this oxygen doesn't have an H it has this four spoil group and so what must happen in the final stages this fuzz for group must be donated to an ADP molecule and replace with an H and once it is replaced with an H it can transform into the more stable ketone state the pyruvate molecule and that's exactly what happens in a final stage we take the smaller Kuehl that is high in energy so it contains very active bonds and that makes it a very good molecule that actually transfers that the spore group onto ADP and so in the presence of adp and h plus we take this molecule and by the action of pyruvate kinase so again we form pyruvate in the last step and this reaction is a phosphorylation reaction so we're using a kinase and we for the pyruvate in the ketone state and that ATP molecule and because this process takes place twice we form two ATP molecules here we form two ATP molecules here so a total of four ATP molecules in stage 5 we use two ATP molecules in stage one and the neck result is we form two ATP molecules in glycolysis per glucose that we actually use up so if we sum all these individual reactions and we basically sum up all these individual energy values keep it in mind that all these take place twice and so we have to multiply these energy values by two for these five steps we basically get the following net result so we have a glucose we have two adp we have two nad plus we have two P eyes that's our net input and then that output is

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Keywords: glycolysis, summary of glycolysis, overview of glycolysis, biochemistry, glycolytic pathway, summary of glycolytic pathway, overview of glycolytic pathway, steps of glycolysis, stages of glycolysis, net result of glycolysis, energy released in glycolysis, breakdown of glucose, cell breakdown of glucose, enzymes of glycolysis, steps of glycolytic pathway

Id: elXjUqZRcE0

Length: 16min 8sec (968 seconds)

Published: Thu May 14 2015