Hello and welcome biologists. Today we are looking at specification point D taken from the OCR specification for A-level biology for respiration and this one today involves the link reaction. We need to know the processes involved here. It's not actually that long but it is a little bit tedious unfortunately. It's one of those things that you'll just need to cover up, write it out, check if you've got it then have another go until you get it right unfortunately. You do need to use specific terminology involved here which you can see there in the specification point. So we had a look at glycolysis in the last lesson, in the last video that we did. We're now going to take a look here at the link reaction which is the second stage involved in the aerobic respiration cycle. So the link reaction. Now, don't forget at the beginning in the glycolysis reaction, we got two molecules of pyruvate for one molecule of glucose that was broken down. So therefore, this whole reaction here, this link reaction is going to occur twice per one molecule of glucose. So. This reaction, the link reaction, is occurring in the matrix of the mitochondria and the pyruvate, which has been made from glycolysis in the cytoplasm, has to be actively transported into the mitochondrial matrix through active transport. Once it's in the matrix we can then undergo the link reaction whereby my pyruvate is turned into acetate. And it does that by the removal of one carbon to form carbon dioxide. So therefore my pyruvate has been decarboxylated. And also, my pyruvate has lost a hydrogen electron to the NAD to form reduced NAD. And this means that my pyruvate has been oxidized or dehydrogenated. Once I've got my acetate, which is a two carbon compound, my acetate combines with coenzyme A to form acetyl coenzyme A. Now, coenzyme A is, as it sounds there, is a coenzyme. And this coenzyme, along with NAD, which is another coenzyme involved in respiration, they both act a little bit like postmen, taking things from one place to another. So in this particular reaction here, my coenzyme is going to take my acetate into the next bit of respiration and then it's going to come back. So my coenzyme A is going to go and drop off my acetate and then my coenzyme will come back and it will be reused to again carry more acetate off again into the Krebs cycle, which is the next stage. So you need to be aware of the products involved per one molecule of glucose. Now again, don't forget that my link reaction is occurring twice per one molecule of glucose because my one molecule of glucose is broken down into two pyruvates in that first stage of glycolysis. So therefore, in the link reaction so far, I have two lots of CO2 that I made, I have two lots of reduced NAD, and I also have two lots of coenzyme that I made. That's just another summary of what is going on here in the link reaction. and that is the specification point so like I said it is quite short but you do need to just go over it rewrite it out and rewrite it out cover it up and rewrite it until you get it spot on and make sure that you know it off by heart guys good luck in your exams please remember do not use the words it they amount or size you could use good scientific terminology to describe and explain your processes thoroughly guys good luck