oh, hello there. i'm at the gym. i don't knowwhy you're here, but i'm going to do some pushups, so you can join me on the floor ifyou want. now, i'm not doing this to show off or anything.i'm actually doing this for science. [pained grunt] you see what happened there?
list of fad diets pros and cons, my arms moved, my shoulders moved, my backand stomach muscles moved, my heart pumped blood to all those different places. prettyneat, huh? well, it turns out that how we make and useenergy is a lot like sports or other kinds of exercise it can be hard work and a little bit complicatedbut if you do it right, it can come with some
tremendous payoffs. but unlike hitting a ball with a stick, it'sso marvelously complicated and awesome that we're still unraveling the mysteries ofhow it all works. and it all starts with a marvelous molecule that is one of you bestfriends: atp. today i'm talking about energy and the processour cells, and other animal cells, go through to provide themselves with power. cellular respiration is how we derive energyfrom the food we eat--specifically from glucose, since most of what we eat ends up as glucose. here's the chemical formula for one moleculeof glucose [c6h12o6]. in order to turn this
glucose into energy, we're going to needto add some oxygen. six molecules of it, to be exact. through cellular respiration, we're goingto turn that glucose and oxygen into 6 molecules of co2, 6 molecules of water and some energythat we can use for doing all our push ups. so that's all well and good, but here'sthe thing: we can't just use that energy to run a marathon or something. first ourbodies have to turn that energy into a really specific form of stored energy called atp,or adenosine triphosphate. you've heard me talk about this before. people often referto atp as the "currency" of biological energy. think of it as an american dollar--it'swhat you need to do business in the u.s. you can't just walk into best buy with a handfulof chinese yen or indian rupees and expect
to be able to buy anything with them, eventhough they are technically money. same goes with energy: in order to be able to use it,our cells need energy to be transferred into adenosine triphosphate to be able to grow,move, create electrical impulses in our nerves and brains. everything. a while back, forinstance, we talked about how cells use atp to transport some kinds of materials in andout of its membranes; to jog your memory about that you can watch it right here. now before we see how atp is put together,let's look at how cells cash in on the energy that's stashed in there. well, adenosine triphosphate is made up ofan nitrogenous base called adenine with a
sugar called ribose and three phosphate groupsattached to it: now one thing you need to know about these3 phosphate groups is that they are super uncomfortable sitting together in a row likethat -- like 3 kids on the bus who hate each other all sharing the same seat. so, because the phosphate groups are suchterrible company for each other, atp is able to do this this nifty trick where it shootsone of the phosphates groups off the end of the seat, creating adp, or adenosine diphosphate(because now there are just two kids sitting on the bus seat). in this reaction, when thethird jerk kid is kicked off the seat, energy is released. and since there are a lot of water moleculesjust floating around nearby, an oh pairing
-- that's called a hydroxide -- from someh2o comes over and takes the place of that third phosphate group. and everybody is muchhappier. by the way? when you use water to break downa compound like this, it's called hydrolysis -- hydro for water and lysis, from the greekword for "separate." so now that you know how atp is spent, let'ssee how it's minted -- nice and new -- by cellular respiration. like i said, it all starts with oxygen andglucose. in fact, textbooks make a point of saying that through cellular respiration,one molecule of glucose can yield a bit of heat and 38 molecules of atp. now, it's worthnoting that this number is kind of a best
case scenario. usually it's more like 29-30atps, but whatever -- people are still studying this stuff, so let's stick with that 38number. now cellular respiration isn't somethingthat just happens all at once -- glucose is transformed into atps over 3 separate stages:glycolysis, the krebs cycle, and the electron transport chain. traditionally these stagesare described as coming one after the other, but really everything in a cell is kinda happeningall at the same time. but let's start with the first step: glycolysis,or the breaking down of the glucose. glucose, of course, is a sugar--you know thisbecause it's got an "ose" at the end of it. and glycolysis is just the breakingup of glucose's 6 carbon ring into two 3-carbon
molecules called pyruvic acids or pyruvatemolecules. now in order to explain how exactly glycolysisworks, i'd need about an hour of your time, and a giant cast of finger puppets each playinga different enzyme, and though it would pain me to do it, i'd have to use words likephosphoglucoisomerase. but one simple way of explaining it is this:if you wanna make money, you gotta spend money. glycolysis needs the investment of 2 atpsin order to work, and in the end it generates 4 atps, for a net profit, if you will, of2 atps. in addition to those 4 atps, glycolysis alsoresults in 2 pyruvates and 2 super-energy-rich morsels called nadh, which are sort of thelove-children of a b vitamin called nad+ pairing
with energized electrons and a hydrogen tocreate storehouses of energy that will later be tapped to make atp. to help us keep track of all of the awesomestuff we're making here, let's keep score? so far we've created 2 molecules of atpand 2 molecules of nadh, which will be used to power more atp production later. now, a word about oxygen. like i mentioned,oxygen is necessary for the overall process of cellular respiration. but not every stageof it. glycolysis, for example, can take place without oxygen, which makes it an anaerobicprocess. in the absence of oxygen, the pyruvates formedthrough glycolysis get rerouted into a process
called fermentation. if there's no oxygenin the cell, it needs more of that nad+ to keep the glycolysis process going. so fermentationfrees up some nad+, which happens to create some interesting by products. for instance, in some organisms, like yeasts,the product of fermentation is ethyl alcohol, which is the same thing as all of this lovelystuff. but luckily for our day-to-day productivity, our muscles don't make alcohol when theydon't get enough oxygen. if that were the case, working out would make us drunk, whichactually would be pretty awesome, but instead of ethyl alcohol, they make lactic acid. whichis what makes you feel sore after that workout that kicked your butt.
so, your muscles used up all the oxygen theyhad, and they had to kick into anaerobic respiration in order to get the energy that they needed,and so you have all this lactic acid building up in your muscle tissue. back to the score. now we've made 2 moleculesof atp through glycolysis, but your cells really need the oxygen in order to make theother 30-some molecules they need. that's because the next two stages of cellular respiration-- the krebs cycle and the electron transport chain, are both aerobic processes, which meansthey require oxygen. and so we find ourselves at the next stepin cellular respiration after glycolosis: the krebs cycle.
so, while glycolysis occurs in the cytoplasm,or the fluid medium within the cell that all the organelles hang out in, the krebs cyclehappens across the inner membrane of the mitochondria, which are generally considered the power centersof the cell. the krebs cycle takes the products of glycolysis -- those carbon-rich pyruvates-- and reworks them to create another 2 atps per glucose molecule, plus some energy ina couple of other forms, which i'll talk about in a minute. here's how: first, one of the pyruvates is oxidized, whichbasically means it's combined with oxygen. one of the carbons off the three-carbon chainbonds with an oxygen molecule and leaves the cell as co2. what's left is a two-carboncompound called acetyl coenzyme a, or acetyl
coa. then, another nad+ comes along, picksup a hydrogen and becomes nadh. so our two pyruvates create another 2 molecules of nadhto be used later. as in glycolysis, and really all life, enzymesare essential here; they're proteins that bring together the stuff that needs to reactwith each other, and they bring it together in just the right way. these enzymes bringtogether a phosphate with adp, to create another atp molecule for each pyruvate. enzymes alsohelp join the acetyl coa and a 4-carbon molecule called oxaloacetic acid. i think that's how you pronounce it. together they form a 6-carbon molecule calledcitric acid, and i'm certain that's how you
pronounce that one because that's the stuffthat's in orange juice. fun fact: the krebs cycle is also known asthe citric acid cycle because of this very byproduct. but it's usually referred to bythe name of the man who figured it all out: hans krebs, an ear nose and throat surgeonwho fled nazi germany to teach biochemistry at cambridge, where he discovered this incrediblycomplex cycle in 1937. for being such a total freaking genius, he was awarded the nobelprize in medicine in 1953. anyway, the citric acid is then oxidized overa bunch of intricate steps, cutting carbons off left and right, to eventually get backto oxaloacetic acid, which is what makes the krebs cycle a cycle. and as the carbons getcleaved off the citric acid, there are leftovers
in the form of co2 or carbon dioxide , whichare exhaled by the cell, and eventually by you. you and i, as we continue our existenceas people, are exhaling the products of the krebs cycle right now. good work. this video, by the way, i'm using a lotof atps making it. now, each time a carbon comes off the citricacid, some energy is made, but it's not atp. it's stored in a whole different kindof molecular package. this is where we go back to nad+ and its sort of colleague fad. nad+ and fad are both chummy little enzymesthat are related to b vitamins, derivatives of niacin and riboflavin, which you mighthave seen in the vitamin aisle. these b vitamins
are good at holding on to high energy electronsand keeping that energy until it can get released later in the electron transport chain. infact, they're so good at it that they show up in a lot of those high energy-vitamin powdersthe kids are taking these days. nad+s and fads are like batteries, big awkwardbatteries that pick up hydrogen and energized electrons from each pyruvate, which in effectcharges them up. the addition of hydrogen turns them into nadh and fadh2, respectively. each pyruvate yeilds 3 nadhs and 1 fadh2 percycle, and since each glucose has been broken down into two pyruvates, that means each glucosemolecule can produce 6 nadhs and 2 fadh2s. the main purpose of the krebs cycle is tomake these powerhouses for the next and final
step, the electron transport chain. and now's the time when you're saying, "sweetpyruvate sandwiches, hank, aren't we supposed to be making atp? let's make it happen,capt'n! what's the holdup?" well friends, your patience has paid off,because when it comes to atps, the electron transport chain is the real moneymaker. ina very efficient cell, it can net a whopping 34 atps. so, remember all those nadhs and fadh2s wemade in the krebs cycle? well, their electrons are going to provide the energy that willwork as a pump along a chain of channel proteins across the inner membrane of the mitochondriawhere the krebs cycle occurred. these proteins
will swap these electrons to send hydrogenprotons from inside the very center of the mitochondria, across its inner membrane tothe outer compartment of the mitochondria. but once they're out, the protons want toget back to the other side of the inner membrane, because there's a lot of other protons outthere, and as we've learned, nature always tends to seek a nice, peaceful balance oneither side of a membrane. so all of these anxious protons are allowed back in througha special protein called atp synthase. and the energy of this proton flow drives thiscrazy spinning mechanism that squeezes some adp and some phosphates together to form atp.so, the electrons from the 10 nadhs that came out of the krebs cycle have just enough energyto produce roughly 3 atps each.
and we can't forget our friends the fadh2s.we have two of them and they make 2 atps each. and voila! that is how animal cells the worldover make atp through cellular respiration. now just to check, let's reset our atp counterand do the math for a single glucose molecule once again: we made 2 atps for each pyruvate during glycolysis. we made 2 in the krebs cycle. and then during the electron transport chainwe made about 34 in the electron transport chain. and that's just for one molecule of glucose.imagine how much your body makes and uses every single day.
don't spend it all in one place now! youcan go back and watch any parts of this episode that you didn't quite get and i really wantto do this quickly because i'm getting very tired. if you want to ask us questions you can seeus in the youtube comments below and of course, you can connect with us on facebook or twitter. [manly grunt]
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