okay now for the purpose of respiration we have to talk a little bit about how ATP is synthesized I know in the previous video I said oh ATP is synthesized by just taking ADP and phosphate and just joining it together but obviously the process is not as straightforward as that you see the ATP and phosphate if you want to join it together it needs energy so if there's no energy no joining it together simple as that so the first way in which it can be joined together is through a process known as substrate linked reaction now for the purpose of this all you just have to understand is in your cells you may have some organic molecules for example glucose and look at what happens to the organic molecule it has been broken down now the catabolism or the breakdown of that organic molecule might release a little bit of energy and that energy is directly used to join ADP and phosphate together okay so substrate linked reaction just means using the energy released from another chemical reaction the phosphate groups and ADP are linked together to form ATP okay so that's the first way in which ATP can be synthesized uh and you must know the definition of substate Link reaction when exactly does this happen again don't worry we will talk about that later okay now the second and more important way in which ATP is synthesized is through a process known as chemiosmosis now chemiosmosis no it does not involve water molecules just because the word osmosis is there now what I'm drawing out here is a phospholipid P layer and as you can see there's a weird looking molecule and that is actually an enzyme and it looks a bit like a fan doesn't it like or like a turbine um um and and that enzyme or protein molecule is actually an ATP synthes now the interesting thing about this enzyme is what it does is that enzyme can actually rotate and when that enzyme rotates the the turbine like part um it will accept an ADP and phosphate join the ADP and phosphate together and release the ATP molecule so that's what the uh enzyme is supposed to to do so I'm just going to remind I'm just going to explain this again when the ATP synthes molecule rotates it will accept the ADP and phosphate joins it together and release the ATP but the caveat here is the ATP synthes must be able to rotate so then comes the more important question what causes the ATP synthes to actually rotate well if you have a fan what causes it to rotate electricity if you have a windmill what causes it to rotate wind but if you have ATP synthes what causes it to rotate here's where it becomes a little bit peculiar it's actually hydrogen ions what the hydrogen ions need to do is the hydrogen ions need to diffuse through that hole that particular hole through the ATP synthes and the diffusion of hydrogen ions through that ATP synthes will cause it to rotate and when it causes that to rotate it will accept ADP phosphate and synthesize ATP molecules so this ATP synthes can generate ATP but it can only do so if it's powered by hydrogen ions so the hydrogen ions have to move from a higher hydrogen ion concentration to a lower hydrogen ion concentration and actually this is an example of facilitated diffusion by the way so the movement of protons or hydrogen ions by the way you can use the word protons or hydrogen ions in the exam uh so the movement of protons or hydrogen ions down the proton gradient through the ATP synthes will generate ATP so you see uh chemiosmosis is actually the main way your cells synthesize ATP not substrate link reaction I mean both can happen both do happen but CH osmosis is the main way the majority of your ATP uh is synthesized so then comes the question where does hydrogen ion come from you see remember respiration is the breakdown of molecules so when the organic molecule for example glucose is broken down the organic molecule releases some energy and that the the slight energy that is released is used to join phosphate and ADP together to make ATP that is substrate link reaction but the braak break down of the organic molecule like glucose will also release hydrogen atoms that hydrogen atoms will eventually split to become hydrogen ions and those hydrogen ions are used to power the ATP synthes and thus produce ATP so this is the purpose of respiration respiration is to break down the organic molecule so that substrate linked reaction can happen and also to harness the hydrogen atoms so that the hydrogen atoms can eventually become hydrogen ions and allow chemiosmosis to take place so this is respiration in a nutshell then of course comes another very important thing okay I want to talk about this you see I'm drawing out the cytoplasm and mitochondrian and in the mitochondrian over here that's the Matrix okay uh of the mitochondrian and the mitochondrian if you remember it's a double membrane organel uh let's focus on the inner membrane which is folded to form those cisti you see the ATP synthes is actually located in the inner membrane I'm only drawing out one ATP synthes but in reality there are you know more than one in the inner membrane that's why it's folded because the more folded it is the more ATP synthes it can contain again I'll talk about that later okay but the point of the matter here is this if you have a glucose molec and you break it down okay remember we wanted to break down the glucose molecule all right so when you break it down over here yes it releases some energy which is used to directly join ADP and phosphates together to ATP substrate link reaction but it also releases out some hydrogen atoms now those hydrogen atoms are not sentient which means to say they don't know where to go because the hydrogen atom is now in the cytoplasm and the ATP synthes which need needs the hydrogen ions eventually uh they are in the inner membrane so they are quite far away so how does the hydrogen atom find its way into uh towards the ATP synthes this is where the cell needs to enlist the help of carriers and these carriers are known as hydrogen carriers and there are two types of hydrogen carriers that we will talk about later anys and feds do not worry we will talk about that in a while and the function of the car is very simple okay they are just molecules by the way and the carrier receives the hydrogen and in chemistry when something receives hydrogen they become reduced okay so the carrier will just receive the hydrogen and they will carry it towards the inner membrane of the mitochondrian where they will actually release out the hydrogen okay towards the ATP synthes or close to the ATP synthes and then the hydrogen carrier becomes oxidized because it releases the uh hydrogen and then it just goes back and tries to receive more hydrogen it's a cycle that happens over here and when the hydrogen is near the ATP synthes the hydrogen will eventually become hydrogen ions don't worry we will talk about that later and then the ATP synthes because it has hydrogen ions because it's powered by the hydrogen ions it can now synthesize ATP so respiration involves so what want you to understand here is the organic molecule such as glucose is broken down and some energy released produces ATP through substrate link reaction no you cannot put SLR in the exam you have to put the word substrate link reaction it also releases hydrogen atoms which are transported by hydrogen carriers towards the ATP synthes so we will talk about all this so this is why this chapter can be quite difficult because there are a a lot of characters involved you have the glucose molecule you have the ATP you have the carrias and you have the ATP synth this but the point of the matter is this glucose is broken down some energy is used to make ATP through substrate link reaction but the main purpose of breaking down the glucose is to get the hydrogen use hydrogen carriers to carry the hydrogen towards the ATP synthes that's basically what's happening and that is how we are going to be talking about the next parts of the chapter so I hope you understand this uh just a little bit to know about the hydrogen carriers okay so the hydrogen carriers are just these molecules known as NS and fads and you do not need to remember the structure of these hydrogen carriers do uh they may show it to you in the exemp they are actually nucleotides by the way but again you do not need to memorize their structures all you just need to know is nads and fads are hydrogen carriers wherein they will just receive the hydrogen atoms uh during respiration and after that what happens they become reduced okay and when they become reduced what happens then is they will carry the hydrogen eventually to the towards the inner mitochondrial membrane that's it it will then become ox ized because it will release the hydrogen what happens to that NAD it will then go back wherever it needs to go to accept more hydrogen it's just a carrier that's basically it the difference between nads and feds will be talked about in future chapters