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Video transcript

mitochondria are organelles that are found in cells and they are responsible for producing ATP or adenosine triphosphate ATP is a molecule that serves as a principal source of energy for cells and for this reason mitochondria are known as the powerhouse of the cell because they provide the cell with power or energy so here's a picture of a mitochondria that was kind of sliced down the middle and let's take a look at its structure so it has an outer membrane and the outer membrane is made up of a lipid bilayer and you might recognize that term as describing the Summa random cell and this lipid bilayer is not permeable to most things but it is permeable to very small molecules and that's because it has certain proteins embedded in it that allow small molecules to pass the mitochondria also has an inner membrane as you can see and the inner membrane is also made up of a lipid bilayer but it is not permeable to small molecules and you'll see in a few moments why this is an important fact to keep in mind and you may have noticed that the inner membrane is not smooth in the way that the outer membrane is but rather it has many folds and these folds are known as well individually each fold is a crista and plurally call them Christy and the reason that the inner membrane is folded into these Christy is because on the inner membrane there are lots of different proteins that are necessary for cellular respiration and by folding the membrane we just increase the surface area and allow a greater amount of membrane to be in a smaller space so it basically just gives us more room to work with the enzymes and more room for cellular respiration to happen and this space between the outer and inner membrane is known as the inter membrane space I'm going to write it over here on the side and then the center of the mitochondria we call that the matrix so now that we've discussed the structure of mitochondria let's let's see how that relates to cellular respiration and what happens here let's go through the steps of cellular respiration which is the process by which we make ATP and then let's see how it relates to the mitochondria so the first step of cellular respiration is glycolysis and what happens during glycolysis is the molecule glucose which is a six carbon molecule gets split into two molecules of pyruvate pyruvate is a three carbon molecule Anglet calluses actually does not happen in the mitochondria it's the only step of cellular respiration that happens in the cytoplasm the next step of cellular respiration is what's known as the PDC or the pyruvate dehydrogenase complex and what happens during the PDC is that pyruvate and remember we have two of them gets converted to a molecule knows known as acetyl co a and you may recognize acetyl co as the molecule that enters the Krebs cycle and the PDC happens in the matrix of the mitochondria so all the enzymes that are involved in the PC are found in the matrix of course as well the next step of cellular respiration is the Krebs cycle and in the Krebs cycle acetyl co a is going to undergo a series of reactions which I'm not going to go into the details of that right now and this happens also in the matrix of the mitochondria and what I'm going to focus on right now is that at the end of the Krebs cycle we produce two molecules nadh and fadh2 and these are electron carriers you'll see in a moment why they're so important and the last step of some of the respiration is the electron transport chain the electron transport chain happens on the inner mitochondrial membrane so on the membrane itself and this is the part we were actually going to make ATP with the help of these electron carriers that we made during the Krebs cycle so let's take a closer look at the inner mitochondrial membrane and see what happens during the electron transport chain so here's a more close-up diagram of the inner mitochondrial membrane let's just orient ourselves let's say that over here is the outer membrane which would make this area over here the cytoplasm of the cell and let's say that over here is the matrix of the mitochondria and here justly what is the inner membrane so you can see the inner membrane is studded with a bunch of these enzymes and these are the enzymes that are involved in the electron transport chain and in case you want to know the names of these various enzymes there over here some of them are pretty long so we're just going to refer to them by numbers this one over here is going to be one that's NADH reductase then this white one that's cytochrome Q this green one is succinate dehydrogenase then we have number three I'm not going to mention the names you can read them if you want then we have cytochrome C over here and then there's number four right over here so we have nadh and fadh2 which were produced during the krebs cycle and these are our electron carriers and I'm going to describe what happens to NADH but the same thing happens to fadh2 so any D H is going to be oxidized or lose electrons so let's write out that reaction NADH will turn into nad plus plus two hydrogen ions plus two electrons so it got reduced and those two like I'm sorry it got oxidized it lost electrons those two electrons are going to go onto enzyme number one so while NADH lost electrons and got oxidized the first enzyme gained electrons or it got reduced but enzyme one is not going to hold on to the electrons it's going to pass them on to the next enzyme which is cytochrome Q so now enzyme number 1s oxidized because it loses electrons but enzyme cytochrome Q gets reduced because it gains electrons and then the same thing will happen with the next enzyme cytochrome Q will pass those two electrons on to the next enzyme and in case you're wondering where this sign enzyme two comes in so fadh2 when it gets oxidized its electrons go directly to enzyme two from there to cytochrome Q from there to three etc but anyways back to what's happening to our NADH so the two electrons are an enzyme 3 then they go to cytochrome C then they go to enzyme 4 and then finally those two electrons are used to reduce oxygen and make water so I'm going to write 1/2 co2 which is the same as one oxygen atom plus 2 H pluses plus those two electrons give us water 2 h plus is plus 2 electrons that's the same thing as saying 2 H so we produce water let's go back to the electrons jumping from one enzyme to the next when these electrons go from one enzyme to the next they're going from a state of higher energy to a state of lower energy and when electrons go from a state of higher energy toastie of lower energy they release energy so I'm just going to write energy kind of coming out of that out of those arrows and that energy is used for something the enzymes in the inner mitochondrial membrane use that energy to do something they use that energy to pump hydrogen ions out from the matrix and into the intermembrane space if you recall the inter membrane space is the space between the inner and outer mitochondrial membrane so we're going to have at the end of this process a whole bunch of hydrogen ions in this inter membrane space and that makes the inter membrane space more acidic sorry not not out there right the outer membrane let's just to make things clear so we're talking about the inter membrane space so the inter membrane space now becomes acidic while the matrix becomes basic and we know that in general molecules like to go from areas of high concentration to areas of low concentration and this inter membrane space has so many high hydrogen ions and they just want to get back into the matrix but if you recall we said that the inner membrane is not permeable even to the tiniest molecules so the H+ ions cannot go through the inner membrane there's only one thing that they can get back into the matrix and that is they can go through this special enzyme known as ATP synthase ATP synthase has special channels in it that will allow H+ ions to pass through so the H+ ions will pass through these special channels in ATP synthase and when they do they're going to cause this axle to turn let's focus now on the bottom part of ATP synthase it has this part of the protein has EDPs adenosine diphosphate and peas or phosphates there are a lot of them are just going to drill one of each and when the axle spins as the H+ ions go through it's going to cause the ADP zenpeace kind of knock into each other and attach so ATP will attach to P and we're finally going to produce ATP the molecule that were trying to get to this entire time let's just mention two terms that are relevant here the first is chemiosmosis chemiosmosis refers to the hydrogen ions passing through the special channels in ATP synthase and then spinning the axle and making ATP and another term you should know is oxidative phosphorylation oxidative phosphorylation while phosphorylation tells if something's being phosphorylated so we're referring to adp being phosphorylated or adding a pea to it and we're making ATP and the term oxidative tells us that the phosphorylation is happening because of oxidation because of the oxidation of NADH and subsequently the oxidation of all these enzymes let's just recap everything that happened here we had nadh and fadh2 which were produced during the krebs cycle they got oxidized they lost electrons those electrons went on to the first enzyme and from there on they went from enzyme to enzyme to enzyme and when those electrons went from enzyme to enzyme they went from a state of higher energy to a state of lower energy when electrons do that they release energy that energy was used to pump hydrogen ions from the matrix into the intermembrane space so we have a bunch of G's of these hydrogen ions in the intermembrane space these hydrogen ions want to get back because there's a high concentration in the intermembrane space on low concentration in matrix but as we explain the inner membrane is not permeable to h+ ions so the only way for them to get back is to go through ETP synthase through the special channels in ATP synthase when they go through they spin the axle that causes this part of the protein to knock ADP and P together and that finally produces ATP and that ATP then provides the cell with the energy that it needs there is one more topic about mitochondria that I'd like to discuss and that is that mitochondria have their own genome so they have one piece of circular DNA it's a lot smaller than the amount of DNA that's found in the nucleus but it allows them to do a lot of things in there own mitochondria are also self-replicating so they can replicate independently of the cell in which they are and because they have their own genome they're able to make their own ribosomal RNA tRNA that's transfer RNA they actually make some of the proteins involved in the electron transport chain I'm just going to abbreviate that etc' so DDT stands for electron transport chain and they also produce parts of the protein ATP synthase it's a rather complex protein and they do produce some parts of it however most of the proteins of the mitochondria are actually encoded for by the nuclear genome the mitochondria even uses a different system of transcription and translation and when I say different I mean different than the nuclear genes and mitochondria even has its own unique genetic code so mitochondria are relatively independent organelles