so in the previous video we talked about the process of glycolysis and at the end of glycolysis the glucose has been broken down into two pyro molecules and you also get two reduced Ned and for ATP molecules in the process uh but the breakdown of the organic molecules is not done so the next reaction after glycolysis has to be the link reaction and for the link reaction to happen the Pyro molecule will first have to Enter the Matrix of the mitochondrian because that is the location of the link reaction as I'm showing you in this particular diagram uh you don't have to know this in detail but the pyate molecule is actively transported into the mitochondrial Matrix and of course by entering the Matrix it will then be able to take part in the link reaction so what exactly is link reaction all about the good news is the link reaction only has three steps decarbox oxidation also known as dehydrogenation in this case and the addition of something called coenzyme a now let's talk about it so remember at the end of glycolysis you get two pyate molecules now I'm only going to focus on one pyrovate molecule first which I've highlighted now the pyate molecule under go DEC car oxil and what exactly does decarbox silation mean decarbox ilation just means the removal of one carbon in the form of carbon dioxide so look at the pyate molecule it had three carbons earlier now it has only two carbon then after that that two carbon molecule will undergo oxidation or dehydrogenation remember once it removes the hydrogen the hydrogen doesn't know where to go so the cell enlists the help of the hydrogen carrier called NAD and once the NAD receives the hydrogen what happens to the NAD you are right the NAD becomes reduced nads uh by the way some students will say my school teacher mentioned something like nadh2 or nadh or nadh plus h instead of the word reduced Ned for the purpose of a levels you can just use the word reduced n and you are fine so don't worry so much about that and look at the uh two carbon molecule you are still left with the two carbon molecule called the aetl group it's good to remember the name of the aetl group now the problem with that acetal group is it needs to go into the next reaction which is called the crap cycle but it needs to be carried or transported into the crap cycle and to be transported into the crap cycle you need to add it to something called coenzyme a now some students will ask me the question what exactly is a co-enzyme a coenzyme is not an enzyme technically even though it's in the name a coenzyme is a molecule required for other enzymes to function do you need to memorize the definition not exactly all right uh some students will also ask me where does this co-enzyme come from it usually if I'm if I oh my God I'm trying to think about it at the top of my head if I'm not mistaken co-enzyme a comes from your diet when you eat a particular type of vitamin called vitamin B5 I think um your your body will convert vitamin B5 into coenzyme a uh they're not going to ask that by the way don't worry so much about it so this co-enzyme a which I represented as a maroon triangle I think it's maroon okay um maroon yeah so the co-enzyme a is needed to carry the aetl group into the crap cycle how does it do so the first thing it does is the co-enzyme a is attached and it becomes something called actil Co a you must know the name of that molecule too so the acety group cannot enter the crap cycle but the acet co a is now able to go into the clap cycle that's basically it uh and of course remember there were two pyate molecules so two pyes will undergo decarbox to give you two carbon dioxide molecules and of course the under go oxidation to give you two reduced NAD and the addition of coenzyme a to give you two acety COA so the summary of the process is pyate under goes decarbox under goes oxidation and added with coenzyme a to become acle COA that's all we have to know for the link reaction