Introduction to Electron Transport Chain

so now that we have a general idea of what oxidative phosphorylation is and what the electron transport chain actually does let's begin by discussing briefly the major types of complexes that we find along the electron transport chain so we have four major types of complexes protein complex one protein complex two protein complex three and protein complex four in addition we also have two very important electron carrier molecules used by the electron transport chain one of them is known as Q which stands for coenzyme q also known as ubiquinone and the other known as another one is known as cytochrome C so in this lecture I'd like to briefly discuss these different types of structures and in the next many lectures to come are basically going to look at the details of what actually happens within each one of these complexes so let's begin with protein complex two one now by the way this is a diagram of only one of the electron transport chains of the many electron transport chains that exist in a single mitochondrial inner membrane so this is the inner mitochondrial membrane this is the mitochondrial matrix and this is the inter membrane space that exists between the two membranes of the mitochondria so protein complex one is also known as NADH dehydrogenase or NADH oxido reductase oxido reductase and that's because this is the protein complex that actually accepts those high-energy electrons from the NADH molecules which were produced in glycolysis as well as the citric acid cycle now this complex is actually a very large complex in fact it consists of about 46 individual polypeptide chains and if we examine the shape of protein complex one will notice that it looks like the letter L so the letter L which basically looks like this contains a horizontal component and a vertical component now the vertical component is basically exposed to the matrix of the mitochondria but the horizontal component this component lies entirely in the membrane the inner membrane of the mitochondria so the entire function of protein complex one is to accept those high-energy electrons from nadh molecules and to move those electrons along a special pathway within the complex that we're going to focus on in detail in a lecture to come and those electrons ultimately are transferred onto the electron carrier molecule known as coenzyme q ubiquinone that we're going to look at in just a moment now this protein complex number one also acts as a proton pump so the fact that we have the movement of electrons within this complex that generates a form of energy that allows us to actually move these H+ ions across this membrane to this side and that ultimately allows us to actually generate a proton electrochemical gradient that will ultimately be used by the ATP synthase molecule to form the ATP molecule so this is protein complex one so once again complex one also known as NADH dehydrogenase or NADH oxido reductase is a very large complex that consists of about 46 individual polypeptide chains it has an L shape that contains a horizontal component found within the inner membrane and the vertical component that lies within the matrix of the mitochondria and the transfer of electrons as we'll see in a future lecture actually takes place within this vertical component of this complex now the function of the complex is to actually exceed eyes.the NADH back to nad plus except those high-energy electrons and then move those high-energy electrons along a specific pathway and that generates an electric current that basically allows us to pump those H+ ions across the membrane for the matrix on the matrix and into the intermembrane space now let's move on or actually since we're on the subject let's look at coenzyme Q so coenzyme q also known as ubiquinone is pretty much this small molecule that is dissolved in the membrane of the mitochondria this is shown here and because it contains a relatively large hydrophobic region it can dissolve easily in the membrane and so it can move across the membrane and what it does is it takes those electrons from protein complex 1 that were received by the NADH molecule and it shuttles it moves those electrons onto protein complex 3 in addition this coenzyme q is also used to actually pick up the electrons received by protein complex 1 and move those molly a move move those electrons onto protein complex 3 so let's move on to protein complex 2 now the entire function of protein complex 2 is to actually accept and extract those high-energy electrons from the fadh2 molecule the fadh2 molecules which are synthesized in the citric acid cycle so if we recall the citric acid cycle there's a step in the citric acid cycle where we basically transform we oxidize succinate into fumarate and in this process we have an enzyme known as succinate dehydrogenase that essentially reduces the fa d in to fadh2 so remember F ad is flavin adenine dinucleotide which is capable of actually receiving extracting those high-energy electrons so these two H+ ions and one electron from each one of these two bonds is extract that and placed onto the fa D to form the fadh2 and actually this succinate dehydrogenase that is used by the citric acid cycle is found within complex to so complex to found on the inside portion of the intermet inner membrane the mitochondria as shown here contains the succinate dehydrogenase that is used by the citric acid cycle and so actually when we synthesize the fadh2 in the citric acid cycle it remains attached onto the succinate dehydrogenase of this protein complex to and within that complex that fadh2 is actually oxidized back into fa d and that allows those two high-energy electrons to be extracted by this complex and as we'll see in a future lecture those electrons are then taken by this coenzyme q carrier our ubiquinone and so ubiquinone is able to shuttle to move the electrons not only from protein complex 1 2 3 but also from protein complex 2 2 3 so protein complex - also known as succinate reductase contains the succinate dehydrogenase enzyme that is used by the citric acid cycle to transform succinate into fumarate in the process forming fadh2 now one important distinction between protein complex 2 and the other protein complexes is protein complex 2 is not a proton pump it does not actually move the protons from the matrix side to the intermembrane side only protein complex 2 and as we'll see in just a moment protein complex 3 and 4 are actually proton pumps and are used to generate electrochemical gradients for protons so let's move on to complex 3 so complex 3 is shown here and this complex is also known as cytochrome C oxidase or Q cytochrome C oxidase and sometimes known as cytochrome reductase and what this proton pump or what this complex does is it accepts those electrons from the q carrier molecule the ubiquinone and then it takes those electrons and transfers them onto another electron Karrie are known as cytochrome C now this just like protein complex one is also proton pump and as a result of the movement of those electrons within this complex that allows the structure to actually pump those protons into the intermembrane space from the matrix of the mitochondria and finally if we examine protein complex for this is essentially where we take those electrons and we use them to reduce oxygen molecules into water molecules so this is where we find the final electron acceptor of the electron transport chain and this also uses the movement of those electrons to pump those protons out of the matrix and into the space between the two membranes and so together protein complex one three and four are basically proton pumps which help establish a proton gradient and then as we'll see in a future lecture that ATP synthase uses that proton gradient to generate those ATP molecules via oxidative phosphorylation and it's called oxidative because protein complex 4 uses oxygen as that final electron acceptor so we see that coenzyme q also known as ubiquinone shown here is basically a small hydrophobic molecule that is dissolved in the inner mitochondrial membrane and it acts as an electron carrier that shallows electron from protein complex 1 or protein complex 2 ultimately to protein complex 3 now in its oxidized form we call it ubiquinone Q and this is what the structure actually looks like and notice we have a long hydrophobic tail in humans the end value is usually 10 and that's why we call it coenzyme q-10 and what happens is the two electrons and two H+ ions are accepted so one electron and one H+ ion is accepted by each one of these groups shown here and here to form the fully reduced four armed we call ubiquinol or qh2 so this structure accepts electrons from either complex one or two to form the reduced form qh2 and then that travels to complex three where it gives off those electrons to complex three which ultimately move along the complex and unto cytochrome C and cytochrome C online coenzyme q is a small water soluble protein so remember this structure is not approaching coenzyme q is not a protein by cytochrome c is a protein and it's a water soluble protein it is bound onto the interim membrane region of complex 3 and once it accepts those electrons it moves and attaches onto protein complex 4 on this side of the complex and then it transfers those electrons which ultimately you is to actually reduce that oxygen and form the water molecules as we'll see in much more detail in lectures to come

Channel: Andrey K

Views: 301,736

Keywords: electron transport chain, introduction to electron transport chain, ETC, complexes of electron transport chain, electron transport chain complexes, ubiquinone, ubiquinol, succinate dehydrogenase, NADH dehydrogenase, NADH oxireductase, complex I, complex II, succinate reductase, Complex III, complex IV, cytochrome c, biochemistry

Id: COMD8yHJtLI

Length: 12min 9sec (729 seconds)

Published: Sat Jun 06 2015