ATP & respiration발음듣기
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ATP & respiration
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Now I'm not doing this just to show off or anything, I'm actually doing this for science, okay.발음듣기
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It's pretty neat, huh? Well, it turns out that how we make and use energy is a lot like sports or other kinds of exercise.발음듣기
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It can be hard work and a little bit complicated, but if you do it right, it comes with some tremendous payoffs.발음듣기
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But unlike hitting a ball with a stick, it's so marvelously complicated and awesome that we're still unraveling the mysteries of how it all works, and it all starts with a marvelous molecule that is one of your best friends, ATP.발음듣기
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(energetic music) Today, I'm talking about the energy and the process our cells and other animals' cells go through to provide themselves with power.발음듣기
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Cellular respiration is how we derive energy from the food that we eat, specifically from glucose since most of what we eat ends up as glucose.발음듣기
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Through cellular respiration, we're going to turn that glucose and oxygen into six molecules of CO2, six molecules of water, and some energy that we can use for doing all of our push-ups.발음듣기
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So that's all well and good, but here's the thing, we can't just use that energy to run a marathon or something.발음듣기
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First, our bodies have to turn that energy into a really specific form of stored energy called ATP or adenosine triphosphate.발음듣기
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You can't just walk into a Best Buy with a handful of Chinese yen or Indian rupees and expect to be able to buy anything with them even though they technically are money.발음듣기
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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.발음듣기
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A while back, for instance, we talked about how cells use ATP to transport some kinds of materials in and out of its membranes.발음듣기
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Now before we see how ATP is actually put together, let's look at how cells can cash in on the energy that's stashed in there.발음듣기
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Well, adenosine triphosphate is made up of a nitrogenous base called adenine with a sugar called ribose and three phosphate groups attached to it.발음듣기
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Now one thing you need to know about these three phosphate groups, is that they are super uncomfortable sitting together in a row like that, like three kids on a bus who hate each other all sharing the same seat.발음듣기
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So because the phosphate groups are such terrible company for each other, ATP is able to do this nifty trick where it shoots one of the phosphate groups off the end of the seat, creating ADP, or adenosine diphosphate, because now, there are just two kids sitting on the bus seat.발음듣기
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And since there are a lot of water molecules just floating around nearby, an OH pairing, that's called a hydroxide, from one of the H2Os comes over and takes the place of that third phosphate group, and everybody is much happier.발음듣기
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By the way, when you use water to break down a compound like this, it's called hydrolysis, "hydro" from water and "lysis" from the Greek word "for separate".발음듣기
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So now that you know how ATP is spent, let's see how it is minted, nice and new, by cellular respiration.발음듣기
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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.발음듣기
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Traditionally, these stages are described as coming one after the other but really everything in the cell, is kind of happening all at the same time.발음듣기
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And glycolysis is just the breaking up of glucose's six-carbon ring into two three-carbon molecules called pyruvic acids or pyruvate molecules.발음듣기
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Now in order to explain how exactly glycolysis works, I'd need about an hour of your time, and a giant cast of finger puppets each playing a different enzyme, and though it would pain me to do it, I would have to use words like phosphoglucoisomerase, but a simple way of explaining it, is like this, if you wanna make some money, you gotta spend some money.발음듣기
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Glycolysis needs the investment of two ATPs in order to work and in the end, it generates four ATPs, for a net profit if you will of two ATPs.발음듣기
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In addition to those four ATPs, glycolysis results in two pyruvates and two super energy-rich morsels called NADH, which are sort of the love children of a B vitamin called NAD+ pairing with energized electrons and a hydrogen to create storehouses of energy that will later be tapped to make ATP.발음듣기
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So far we've created two molecules of ATP and two molecules of NADH, which will be used to power more ATP production later. Now, a word about oxygen.발음듣기
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Glycolysis, for example, can take place without oxygen, which makes it an anaerobic process.발음듣기
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In the absence of oxygen, the pyruvates formed through glycolysis gets rerouted into a process called fermentation.발음듣기
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For instance, in some organisms, like yeasts, the product of fermentation is ethyl alcohol, which is the same thing as all of this lovely stuff.발음듣기
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But luckily for our day-to-day productivity, our muscles don't make alcohol when they don't get enough oxygen.발음듣기
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If that were the case, working out would make us drunk, which actually would be pretty awesome but instead of ethyl alcohol, they make lactic acid.발음듣기
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So, your muscles used up all the oxygen they had and they had to kick into anaerobic respiration in order to get the energy that they needed.발음듣기
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Now we've made two molecules of ATP through glycolysis, but your cells really need the oxygen in order to make the other 30-some molecules that they need.발음듣기
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That's because the next two stages of cellular respiration, the Krebs Cycle and the electron transport chain, are both aerobic processes, which means that they require oxygen.발음듣기
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So, while glycolysis occurs in the cytoplasm or the fluid medium within the cell that all the organelles hang out in, the Krebs Cycle happens across the inner membrane of the mitochondria, which are generally considered the power centers of the cell.발음듣기
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Those carbon-rich pyruvates and reworks them to create another two ATPs per glucose molecule, plus some energy and a couple of other forms, which I'll talk about in a minute. Here's how.발음듣기
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First, one of the pyruvates is oxidized, which basically means that it's combined with oxygen.발음듣기
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One of the carbons off the three-carbon chain bonds with an oxygen molecule and leaves the cell as CO2.발음듣기
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They are the proteins that bring together the stuff that needs to react with each other, and they bring them together in just the right way.발음듣기
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These enzymes, for example, bring together a phosphate with an ADP, to create another ATP molecule for each pyruvate.발음듣기
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Together they form a six-carbon molecule called citric acid and I'm certain that that's how you pronounce that one because yeah, it's the stuff that's in orange juice.발음듣기
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(lively piano music) Fun fact, the Krebs Cycle is also known as the Citric Acid Cycle because of this very byproduct.발음듣기
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Hans Krebs, an ear, nose, and throat surgeon who fled Nazi Germany to teach biochemistry at Cambridge, where he discovered this incredibly complex cycle in 1937.발음듣기
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For being such a total freaking genius, he was awarded the Nobel Prize for Medicine in 1953.발음듣기
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Anyway, the citric acid is then oxidized over a bunch of intricate steps, cutting carbons off left and right, to eventually get back to oxaloacetic acid, which is what makes the Krebs Cycle a cycle.발음듣기
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And as the carbons get cleaved off the citric acid, there are leftovers in the form of CO2 or carbon dioxide, which are exhaled by the cell, and eventually by you.발음듣기
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You and I, as we continue our existence as people, are exhaling the products of the Krebs Cycle right now.발음듣기
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Now, each time a carbon comes off of the citric acid, some energy is made, but it's not ATP.발음듣기
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These B vitamins are good at holding onto high energy electrons and keeping that energy until it can get released later in the electron transport chain.발음듣기
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In fact, they're so good at it, that they show up in a lot of those high-energy vitamin powders that the kids are taking these days.발음듣기
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NAD+s and FADs are like batteries, big awkward batteries that pick up hydrogen and energized electrons from each pyruvate, which in effect charges them up.발음듣기
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Each pyruvate yields three NADHs and one FADH2 per cycle, and since each glucose has been broken down into two pyruvates that means each glucose molecule can produce six NADHs and two FADH2s.발음듣기
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The main purpose of the Krebs Cycle is to make these powerhouses for the next and final step, the electron transport chain.발음듣기
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And now comes the time when your saying, "Sweet pyruvate sandwiches, Hank, "aren't we supposed to be making ATP here?발음듣기
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Well friends, your patience is finally paying off because when it comes to ATPs, the electron transport chain is the real moneymaker.발음듣기
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Well, their electrons are going to provide the energy that will work as a pump along a chain of channel proteins across the inner membrane of the mitochondria where the Krebs Cycle occurred.발음듣기
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These proteins will swap these electrons to send hydrogen protons from inside the very center of the mitochondria, across its inner membrane to the outer compartment of the mitochondria.발음듣기
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But once they're out, the protons want to get back to the other side of the inner membrane, because there's a lot of other protons out there and as we've learned, nature always tends to seek a nice, peaceful balance on either side of a membrane.발음듣기
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So all of these anxious protons are allowed back in through a special protein called ATP synthase.발음듣기
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And the energy of this proton flow drives this crazy spinning mechanism that squeezes some ADP and some phosphates together to form ATP.발음듣기
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So, the electrons from the 10 NADHs that come out of the Krebs Cycle, have just enough energy to produce roughly three ATPs each.발음듣기
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Now just to check, let's reset our ATP counter and do the math for a single glucose molecule once again.발음듣기
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We made two during the Krebs Cycle, and then during the electron transport chain we made about 34.발음듣기
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