NEW Glycolysis Part 2 4 The Preparatory Phase Questions

hi welcome back to biochemistry my name is Kevin Toof make sure to like this video And subscribe to the channel for future videos and notifications all right so in the next couple or few videos we're going to be talking about glycolysis and in the previous video went over the basics of glycolysis not anything related to these structures the enzymes anything like that what the purpose of it is where it occurs everything of that nature in the next two videos we're going to go over the two main phases of glycolysis and we're instead of looking at this from you know strict organic perspective or energy or you know thermodynamics all that stuff that makes things confusing we're just going to look at this from structural and and very logical visual way so that hopefully this will make sense all right so there's some things I've left out but the the the the basics that you would need to know for any biochemistry course about the pathway we're going to go over in these next two videos like said in the previous video the two main parts of glycolysis are generally called number one the Preparatory or investment phase and the second part is the payoff phase and we'll talk about why they're called that as we go through the video and then we have some review questions at the very end of each video all right so the first thing want to do is say what we start out with what is the main purpose of glycolysis generally what people have told you in the past is glycolysis is is metabolic pathway that basically takes glucose or six carbon sugar and breaks it down into two three carbon fragments all right so in general we're going to look at this with respect to glucose there are some other ones that can be broken down by glycolysis but let's focus on glucose because that's the main idea and this is the this is the cyclic structure of glucose all right first enzyme step one hexokinase all right hexo what does that mean hexo usually refers to carbon sugar right hexos is six carbon sugar glucose is six carbon sugar what's kinas from what we talked about before kinas is an enzyme that uses ATP to add phosphate group to some molecule so hexokinase should add phosphate to glucose because that's the hexos here so the phosphate donor is this ATP and it's going to transfer phosphate specifically onto this position right there it's going to replace that hydrogen with phosphate and that we see right here here you see the whole phosphate group right here okay now if you remember back to your numbering system this is carbon six on glucose so we just call it glucose 6 phosphate okay sometimes they'll abbreviate that as glc6p glucose 6 phosphate all we did is we transferred phosphate from ATP to that oxygen right there on glucose and when we transfer the phosphate we get out an ad DP okay now this step right here is little confusing okay this is glucose 6 phosphate right here this molecule that you see here is actually fructose 6 phosphate so how do we go from glucose 6 phosphate to fructose 6 phosphate well glucose and fructose are isomers of each other they're isomers they're actually constitutional isomers they're the same number and type of atoms so literally what this enzyme does is just going to isomerize glucose into fructose along with the phosphate that's on there okay and it's going to ultimately do that through use of this carbon right here which happens to be the anomeric carbon very reactive carbon and it's going to take this Six membered Ring into five membered ring which is fructose okay key things to understand here this position right over here that's the six phosphate okay and one one other thing want to note for the next step this is position one right there that is position one on fructose okay so it literally takes the six membered glucose 6 phosphate and turns it into the five membered ring fructose 6 phosphate again if you count the number of carbons on each of these first three molecules it's still six they're all six carbons okay next enzyme Next Step phosphofructokinase One typically abbreviated as pfk1 we'll talk more about this enzyme in another video videos but ice to say it's the rate limiting step of glycolysis it's also the main regulatory point of glycolysis okay we already have phosphate on the sixth position why do you think said this is the one position well it's kise so it's going to phosphorate something it's going to phosphorate phosphor fructo molecule which is handy because this is phosphor fructo molecule it's fructo 6 phosphate so we're going to phosphorated at the one position and that's what you see right here you now see not only do we have phosphate still on the sixth position oops but we also now have one on the one position okay so now instead of being fructose 6 phosphate this one is termed fructose 16 bis phosphate now there's two phosphates one on the one in six positions okay where do you think that phosphate came from well it came from ATP okay and then when you transfer the phosphate onto this position right here you get out ADP all right now one thing want to talk to you about very quickly has to do with the next enzyme which I'll go ahead and say is termed alalas you've probably heard since General biology maybe anatomy and physiology depending on the curriculum that glycolysis takes one six carbon sugar and breaks it into two three carbon sugars and up until biochim you probably haven't known why it does that or how but alalas this next enzyme this is the enzyme that does this this is the enzyme that breaks the six carbon sugar into three or two three carbon fragments okay because this molecule right here you don't really need to know the name of it but fructus 16 is phosphate this is six carbons okay so we're going to do little bit of detail on alalas because it's actually kind of an important enzyme here okay so let's talk about it the first activity of alalas I'll go ahead and read this right here because went ahead and wrote this alalas has two important activities the first is to open the ring just termed ring opening reaction so up until this point all these structures that you've seen before they're all in their cyclic form and that's the only way they exist in this pathway alalas uses or it it opens the ring through the anomeric carbon that's print there but it suffices that he uses the reactive nature of this anomeric carbon to open the ring into this linear form okay so the only way that the main reaction of alel which is Activity 2 can proceed is when you have fructose again this molecule right here this is still this is still fructose 16 bis phosphate it's just in its linear form the previous form was its cyclic form so this is linear the the only way the main activity the second one of alvas can proceed is with this molecule in its linear form so first activity open up the ring and this I've drawn it in the Fisher projection form but you can draw it any way you want okay the second activity is its cleavage of of the six carbon fragment this is actually the step right here this is the step where you break the six carbon sugar into two three carbon fragments so let me read this Al's second activity is to split the six carbon sugar into two three carbon fragments termed g3p and dhap g3p stands for glycer aldy 3 phosphate dhap stands for dihydroxy acetone phosphate but you can abbreviate those note that these two products are different okay it breaks it into two different products and the reaction is termed retroaldol addition in case you are wondering so what you've heard since gen bio anatomy and physiology cell bio Etc that glycolysis splits six carbon sugar into two three carbon sugars this is directly accomplished by alel this is the enzyme that does what you've heard up in even maybe since high school okay so if you really wanted to look at what the structures how they're normally drawn they're drawn like this one which this one happens to be glycer Al this one happens to be excuse me this is dihydroxy acetone phosphate right here and this one which is the most important as we'll talk about in minute called glycer alide 3 phosphate or g3p okay now dhap in terms of glycolysis is useless it can't proceed in that form so there's another another enzyme called trios phosphate isomerase which literally takes dhap and converts it into g3p so if you have one glucose that's six carbons it's going to split it initially into two different three carbon fragments dhap and g3p But ultimately the dhap will get converted to g3p because dhap is useless so in other words per one glucose we'll have two g3ps at the end of this if have 100 glucoses I'll have 200 g3ps so however many glucoses you put in the glycolysis just double that and that number is the number of g3ps ultimately because of this enzyme right here trios phosphate isomerase okay and the g3ps we're not going to finish that in this video but will say that the g3p continues into what we call the payoff phase of glycolysis and that's going to be covered in the next video now before we conclude this video it's really important to look at some test type of questions that we can ask all right number one how many carbon atoms do each of the molecules that is glucose through fructose 16 phosphate half that's all the enzymes prior to alalas remember alalas is the splitting enzyme so how many carbons do those have well those all have six carbons that's the thing that you've heard about since you in gen bio okay they all have six carbons so number two what is that really important facet of alalas that you have heard about since gen bio well alalas directly is the enzyme that splits the six carbon sugar in this case it happens to be glucose into two three carb fragments that happen to be different from each other okay so number three that's going to lead us into this alalas or in general we say glycolysis takes six carbon sugar called and that is glucose which I'll abbreviate and splits it into two blank carbon fragments well it's going to split it into two three carbon fragments the fragment for number three that continues into the payoff phase of glycolysis is what well did we say DH AP continues no it has to get converted into g3p to be useful this is our useful molecule g3p so that's what I'm going to put in this blank the fragment from number three that continues into the payoff phase of glycolysis is called g3p or in reality it's called glycer aldhy 3 phosphate all right does the investment phase of glycolysis this what we just talked about yield energy or does it consume I.E burn energy and by energy mean things like ATP or nadh well if you go back and look at the pathway did we actually get any ATP out of it no in step one hexokinase we had to burn an ATP in other words consume it we didn't get it out instead we got out an ADP that doesn't help us we had to put in the ATP so we consumed that and then in pfk1 step three we had to burn another ATP so whenever say we burn an ATP that's that's typical way of talking about this it's sort of slang in Biochemistry burn ATP means it's loss okay you lost that ATP because you had to use it okay so does it do we yield energy or consume it the answer is we consume or burn it and specifically for number six what is the net gain or loss of energy from the investment phase we lost to ATP we lost to at TP now haven't explained this yet but that seems bad but it turns out in the payoff phase the last half of this pathway we're going to more than make up for that loss of 2 ATP we're actually going to get four atps out of the payoff phase plus two nadhs as we'll find okay there's no nadh that we deal with in this part of the pathway that's the second part here's question where in the eukaryotic cell does glycolysis occur glycolysis only occurs in the cytool OR cytoplasm does not occur in the mitochondria it does not occur in organel it only occurs in the cytool very important Point okay then number eight this is kind of thinking type of question glycolysis can actually catabolize other sugars as well but generally they have to have six carbon atoms which of the following sugars might be catabolized through this pathway well so we're really determining which ones have six carbons and then those are the ones that will get catabolized through glycolysis now it's not exactly the same pathway they're going to enter at different points but they do get broken down through this pathway so what about fructose does that get catabolized through glycolysis the answer is yes because fructose has six carbons what about ribos ribos would not because ribos has five carbons ribos along with deoxy ribos which is also in this list they have separate pathway for their for their catabolism what about galactose galactose is also six carbon sugar that one will get catabolized through this pathway what about xylos now xylos also like xylulose those are both five carbon sugars they do not get catabolized this way and that is the same for ribulose which is the derivative of ribos ribulose is also five carbon sugar in fact xylos en zose ribulose ribos one of their Pathways for catabolism is actually the pentos post phosphate pathway which is another pathway we'll discuss in another playlist then finally Manos what about Manos the answer is yes Manos is six carbon sugar that can get catabolized through glycolysis and we cover that in other videos okay so those are some really important thinking questions about glycolysis specifically the investment phase in the next video we're going to cover the payoff phase and we're going to compare and contrast it to this phase as we said in the Preparatory SL investment phase we had to burn 2 ATP that means we lost 2 ATP but as it turns out we're going to totally and more than make up for that loss in the next few reactions in the next video so make sure to like this video subscribe to the channel for future videos and notifications hope this helped see you soon