Articles, Blog

ATP & Respiration: Crash Course Biology #7

October 10, 2019

Oh, hello there. I’m at the gym. I don’t know
why you’re here, but I’m going to do some pushups, so you can join me on the floor if
you 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? My arms moved, my shoulders moved, my back
and stomach muscles moved, my heart pumped blood to all those different places. Pretty
neat, huh? Well, it turns out that how we make and use
energy is a lot like sports or other kinds of exercise It can be hard work and a little bit complicated
but if you do it right, it can come with some tremendous payoffs. 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 you best
friends: ATP. Today I’m talking about energy and the process
our cells, and other animal cells, go through to provide themselves with power. Cellular respiration is how we derive energy
from the food we eat–specifically from glucose, since most of what we eat ends up as glucose. Here’s the chemical formula for one molecule
of glucose [C6H12O6]. In order to turn this glucose into energy, we’re going to need
to add some oxygen. Six molecules of it, to be exact. Through cellular respiration, we’re going
to turn that glucose and oxygen into 6 molecules of CO2, 6 molecules of water and some energy
that we can use for doing all our push ups. 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. First our
bodies 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 refer
to ATP as the “currency” of biological energy. Think of it as an American dollar–it’s
what you need to do business in the U.S. You can’t just walk into Best Buy with a handful
of Chinese yen or Indian rupees and expect to be able to buy anything with them, even
though 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, for
instance, we talked about how cells use ATP to transport some kinds of materials in and
out 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 of
an nitrogenous base called adenine with a sugar called ribose and three phosphate groups
attached to it: Now one thing you need to know about these
3 phosphate groups is that they are super uncomfortable sitting together in a row like
that — like 3 kids on the bus who hate each other all sharing the same seat. So, because the phosphate groups are such
terrible company for each other, ATP is able to do this this nifty trick where it shoots
one 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 the
third jerk kid is kicked off the seat, energy is released. And since there are a lot of water molecules
just floating around nearby, an OH pairing — that’s called a hydroxide — from some
H2O comes over and takes the place of that third phosphate group. And everybody is much
happier. By the way? When you use water to break down
a compound like this, it’s called hydrolysis — hydro for water and lysis, from the Greek
word for “separate.” So now that you know how ATP is spent, let’s
see how it’s minted — nice and new — by cellular respiration. Like I said, it all starts with oxygen and
glucose. 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 worth
noting that this number is kind of a best case scenario. Usually it’s more like 29-30
ATPs, but whatever — people are still studying this stuff, so let’s stick with that 38
number. Now cellular respiration isn’t something
that 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 stages
are described as coming one after the other, but really everything in a cell is kinda happening
all 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 this
because it’s got an “ose” at the end of it. And glycolysis is just the breaking
up of glucose’s 6 carbon ring into two 3-carbon molecules called pyruvic acids or pyruvate
molecules. 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’d have to use words like
phosphoglucoisomerase. But one simple way of explaining it is this:
If you wanna make money, you gotta spend money. Glycolysis needs the investment of 2 ATPs
in order to work, and in the end it generates 4 ATPs, for a net profit, if you will, of
2 ATPs. In addition to those 4 ATPs, glycolysis also
results in 2 pyruvates and 2 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. To help us keep track of all of the awesome
stuff we’re making here, let’s keep score? So far we’ve created 2 molecules of ATP
and 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 stage
of it. Glycolysis, for example, can take place without oxygen, which makes it an anaerobic
process. In the absence of oxygen, the pyruvates formed
through glycolysis get rerouted into a process called fermentation. If there’s no oxygen
in the cell, it needs more of that NAD+ to keep the glycolysis process going. So fermentation
frees 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 lovely
stuff. But luckily for our day-to-day productivity, our muscles don’t make alcohol when they
don’t get enough oxygen. 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. Which
is what makes you feel sore after that workout that kicked your butt. 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,
and so you have all this lactic acid building up in your muscle tissue. Back to the score. Now we’ve made 2 molecules
of ATP through glycolysis, but your cells really need the oxygen in order to make the
other 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 means
they require oxygen. And so we find ourselves at the next step
in 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 Cycle
happens across the inner membrane of the mitochondria, which are generally considered the power centers
of 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 in
a couple of other forms, which I’ll talk about in a minute. Here’s how: First, one of the pyruvates is oxidized, which
basically means it’s combined with oxygen. One of the carbons off the three-carbon chain
bonds with an oxygen molecule and leaves the cell as CO2. What’s left is a two-carbon
compound called acetyl coenzyme A, or acetyl coA. Then, another NAD+ comes along, picks
up a hydrogen and becomes NADH. So our two pyruvates create another 2 molecules of NADH
to be used later. As in glycolysis, and really all life, enzymes
are essential here; they’re proteins that bring together the stuff that needs to react
with each other, and they bring it together in just the right way. These enzymes bring
together a phosphate with ADP, to create another ATP molecule for each pyruvate. Enzymes also
help 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 called
citric acid, and I’m certain that’s how you pronounce that one because that’s the stuff
that’s in orange juice. Fun fact: The Krebs Cycle is also known as
the Citric Acid Cycle because of this very byproduct. But it’s usually referred to by
the name of the man who figured it all out: 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. For being such a total freaking genius, he was awarded the Nobel
Prize in Medicine in 1953. 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. 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. You and I, as we continue our existence
as people, are exhaling the products of the Krebs Cycle right now. Good work. This video, by the way, I’m using a lot
of ATPs making it. Now, each time a carbon comes off the citric
acid, some energy is made, but it’s not ATP. It’s stored in a whole different kind
of molecular package. This is where we go back to NAD+ and its sort of colleague FAD. NAD+ and FAD are both chummy little enzymes
that are related to B vitamins, derivatives of Niacin and Riboflavin, which you might
have seen in the vitamin aisle. These B vitamins are good at holding on to high energy electrons
and keeping that energy until it can get released later in the electron transport chain. In
fact, they’re so good at it that they show up in a lot of those high energy-vitamin powders
the kids are taking these days. 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. The addition of hydrogen turns them into NADH and FADH2, respectively. Each pyruvate yeilds 3 NADHs and 1 FADH2 per
cycle, and since each glucose has been broken down into two pyruvates, that means each glucose
molecule can produce 6 NADHs and 2 FADH2s. The main purpose of the Krebs Cycle is to
make these powerhouses for the next and final step, the Electron Transport Chain. And now’s the time when you’re saying, “Sweet
pyruvate 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. In
a very efficient cell, it can net a whopping 34 ATPs. So, remember all those NADHs and FADH2s we
made in the Krebs Cycle? 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. 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. 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. So all of these anxious protons are allowed back in through
a special protein called ATP synthase. And the energy of this proton flow drives this
crazy 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 energy
to 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 world
over make ATP through cellular respiration. Now just to check, let’s reset our ATP counter
and 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 chain
we 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! You
can go back and watch any parts of this episode that you didn’t quite get and I really want
to do this quickly because I’m getting very tired. If you want to ask us questions you can see
us in the YouTube comments below and of course, you can connect with us on Facebook or Twitter. [manly grunt]


  • Reply Alexandra Kamberos July 18, 2019 at 6:23 am

    It’s been 7 years and I’m gonna need that enzyme puppet show now… 😅

  • Reply cellogirl11RW July 19, 2019 at 4:19 am

    OMG! I get it now!! Thank you so much!

  • Reply Alexandra Marra July 21, 2019 at 1:55 pm

    My exam is in 10 mins, when is yours?

  • Reply Matt Flavell July 22, 2019 at 12:31 pm

    speak english

  • Reply poswithjess July 25, 2019 at 4:20 am

    When I put this in slow mo it makes me feel like hes talking to me like an idiot hahaha

  • Reply Caitlin Kubina July 25, 2019 at 2:29 pm

    I'm confused. For the electron transport chain, we have 10 NADH, but the Kreb cycle produced 6 NADH, right? And glycolysis only produces two. Shouldn't there only be 8 NADH for the electron transport chain?

  • Reply Evan Halpern July 28, 2019 at 6:31 pm

    Great video.

  • Reply Myriam A July 29, 2019 at 6:42 am

    I wish I had this video 13 years ago when I got bio courses

  • Reply Slay Mone August 1, 2019 at 2:29 pm

    Chinese Yen?

  • Reply uumonki August 4, 2019 at 7:26 am

    chinese yen??

  • Reply J. Nguyen August 4, 2019 at 10:14 pm

    I really needed you to break down Krebs cycle ALL the way down

  • Reply Nicola Marino August 5, 2019 at 2:27 pm

    I know I've wasted a lot of time when I begin playing these at 1.25

  • Reply grndragon7777777 August 6, 2019 at 4:54 pm

    Adenosine triphosphate
    Adenosine triphosphate
    Adenosine triphosphate

  • Reply TPipkin97 August 9, 2019 at 2:48 am

    While the information in these videos is usually spot on, I just wanted to mention that ATP is NOT a stored form of energy. Whenever ATP is produced, it is used immediately.

  • Reply Varasram Duggu August 11, 2019 at 4:04 pm

    How many hydrogen ions make 1atp in ETS

  • Reply Jessie G August 14, 2019 at 8:15 am

    Cell bio exam in two weeks 😢🙏

  • Reply kfudnaweehhhh August 18, 2019 at 12:59 pm

    Hank you are awesome, learning a lot more here than I ever did in school

  • Reply C.L Mckenzie August 21, 2019 at 10:50 pm

    So humans naturally make citric acid 🤔

  • Reply Gamos96 August 23, 2019 at 12:42 am

    Is the kreb's cycle taking place in the matrix of the mitochondrion or the inner membrane ?

  • Reply Frost Rusher August 23, 2019 at 2:46 pm

    Im in high school. This started very simple until the glycolysis part.

  • Reply David Jones August 25, 2019 at 10:34 pm

    just wonder if he really understands what he is talking about since he is ATP = atypic dude..?

  • Reply song s August 28, 2019 at 2:52 pm

    I m in 9th class

  • Reply Rohith Raman August 29, 2019 at 9:49 am

    ATP is literally the currency of biological energy ATP = 80p (eighty pence)

  • Reply Adam Wojcik August 29, 2019 at 5:41 pm

    Aren't JEN Japanese currency ? Not Chinese ?

  • Reply Kool Kids August 30, 2019 at 11:34 pm

    I'm only in elementary school so I don't have to worry about exams,.. But I have to take I read, I learn and so on UHHHHHH

  • Reply Ian Davvexx Viernesxxzzs August 31, 2019 at 3:40 am

    Can i get a TOTAL GENERATED ATP DIAGRAM pleaseee??? Anyone can help me………..i need that for my recitation on monday

  • Reply maria lopez August 31, 2019 at 3:16 pm


  • Reply Donald McIntyre August 31, 2019 at 5:04 pm

    Chinese Yuan
    Japanese Yen

  • Reply Abi September 5, 2019 at 2:54 am

    Did he combine Pyruvate Oxidation into Glycolysis or the Citric Acid Cycle?

  • Reply Akselino the great September 5, 2019 at 6:56 am

    it's Chinese yuan, yen is Japanese

  • Reply Anessa Baker September 5, 2019 at 3:06 pm

    plz pray for me im watching this 5 min before a mid term but i got distracted reading comments

  • Reply Bobby Poly September 5, 2019 at 3:31 pm

    you really need to get fit! lol

  • Reply maya hatem September 6, 2019 at 11:29 pm

    When u keep rewinding till u understand the lesson and u know that tomorrow u will forget what u learned

  • Reply Gita Agustiguna September 7, 2019 at 12:47 pm

    Who from Indonesia?

  • Reply SABA MF September 7, 2019 at 4:52 pm

    BIO152 Mid Sem 🙁

  • Reply Mackenzie Craner September 11, 2019 at 3:52 pm

    His philosophy courses helped me so much. But I absolutely do not understand any of his bio lectures. I'm sooooo looosssttt

  • Reply Fisher Jones September 12, 2019 at 1:17 am

    My teacher told me to watch this 🤡

  • Reply Max Gargasz September 12, 2019 at 6:28 pm

    Hank Green talks to you like he's your super genius drunk uncle

  • Reply Luna September 14, 2019 at 11:23 am

    If it doesn't really interest you, It's hard! I got to go back a few seconds every time because the information can't enter my brain right

  • Reply Addy Schultz September 15, 2019 at 9:52 pm

    Everyone ignore this comment it’s for my notes ty

    7:07. 5:46

  • Reply Macey Abon September 16, 2019 at 1:33 pm

    I'm cramming for bio senior high lessons ksksksksks

  • Reply KNFF ZORDOD September 16, 2019 at 3:02 pm

    Asking crash course. Is it really all that neccesary for us 10th graders to learn ALL OF THIS.

  • Reply Giraffelily September 16, 2019 at 7:20 pm

    Any A level Bio students?

  • Reply Isabella Bohr September 18, 2019 at 1:00 am

    watching this for my ap bio test cuz I decided I needed to suffer as a high school sophomore 🙁

  • Reply Sarah Padilla September 19, 2019 at 6:09 pm

    send good thoughts I have a bio exam tmrw lol

  • Reply Erica Energy Healer September 20, 2019 at 1:10 am

    You are amazing and funny!!!! I know is a big group of people putting these videos together and I want to say you guys are all amazing!!! I love these explanations!!! All the visuals help out so much for my Biology Class! Thank you so much!!!💯💯💯

  • Reply Satendr Singh September 20, 2019 at 11:57 am

    I thought bio was easy by this……

  • Reply Braydon September 22, 2019 at 12:37 am

    But yen is Japanese

  • Reply Adam c September 22, 2019 at 3:01 pm

    The editors of this vid, have to stop cutting him off.. It makes the videos WAY TOO FAST. It's hard to absorb the info.

  • Reply Bianka Feher September 23, 2019 at 5:56 pm


  • Reply Brandon Johnson September 23, 2019 at 6:53 pm

    What youtube videos does this guy watch to get ready for HIS presentations?

  • Reply Jonathan Lee September 25, 2019 at 11:40 pm

    This was the most boring"educational" video I have ever been required to watch.

  • Reply Piano Cover September 27, 2019 at 12:30 pm

    Y I found this after I have just finished my FINAL EXAM😭

  • Reply Elizabeth Parisi September 29, 2019 at 12:13 pm

    Hank has a great butt >.>

  • Reply marduv September 29, 2019 at 10:34 pm

    Very informative, but very confusing still with the interesting comparisons … am i the only one?

  • Reply Madeline Ha September 30, 2019 at 3:39 am

    when you only click on the video because the thumbnail looks like bacon..

  • Reply Crystal Michelle September 30, 2019 at 7:01 am

    I thought the kreb cycle occurs in the matrix of the mitochondria 🤔

  • Reply Juan Rueda September 30, 2019 at 4:48 pm

    impressive but when i punch a tree my hand hurts

  • Reply hannah bittar October 3, 2019 at 2:52 am

    GUYS !!!!! 10:54 there's been an error in the animation. The 2 pyruvates yield 6 NAHD total, not 10!! The animation says 10. am i tripping why has no one else said anything??

  • Reply azalia belle October 3, 2019 at 3:08 pm

    Woah amazing, only a molecule of glucose there are alot separate stages going on thru cellular respiration, thank God I found this channel. Big help! fun and a lot easier to understand

  • Reply Julia Gipson October 3, 2019 at 9:00 pm

    Having a panic attack from my bio course breezing through this and moving on in 45 min.
    With attention and learning issues, I must work 6x as hard to understand simple concepts.

    Your program has really helped me and others like myself to stay afloat.

    Thank you sooo very much!!

  • Reply Prince Rayn October 3, 2019 at 9:55 pm

    Did you guys already made videos about transpiration, photorespiration, and CAM plants? Because I need those, but YouTube doesn't seem to have it.

    Please make videos on transpiration, photorespiration, and CAM plants if you haven't yet, thank you 🙂

  • Reply Warhawk 837 October 4, 2019 at 3:20 pm

    This video is only 13 minutes yet it feels like I just watched a 2 hour explanation and I'm lost

  • Reply StrangerSarah*:. October 5, 2019 at 5:46 pm

    bro what about link reaction?

  • Reply Theresa Hardy October 6, 2019 at 12:50 pm

    i wish there were quizzes at the end

  • Reply yung gio October 7, 2019 at 3:27 am

    are u even speaking english, im so done for my test.

  • Reply Aquila11 October 7, 2019 at 11:52 pm

    Where'd you get that shirt?

  • Reply Charlie Westemeyer October 8, 2019 at 1:16 am

    How was the first energy molecule made?

  • Reply Jenna Hauser October 8, 2019 at 1:31 am

    roses are red, my brothers feet smell
    mitochondira …

  • Reply Jenna Hauser October 8, 2019 at 1:45 am

    people saying this is their semester of biology? I was taught this all in two weeks. I have three days to study for our exam.

  • Reply Little Tangerine October 8, 2019 at 5:52 am

    I don't remember any of this.

  • Reply Rohit Kajla October 8, 2019 at 12:09 pm


  • Reply Meredith Ohotto October 8, 2019 at 1:32 pm

    Still don't get it…

  • Reply Brandan Whiteman October 8, 2019 at 4:57 pm

    Yen is currency for Japan yuan is for china

  • Reply Kate Brumfield October 8, 2019 at 6:43 pm

    I need the hour long glycolysis explanation

  • Reply abbey olden October 9, 2019 at 3:18 am

    Hank boo you could get it

  • Reply Dylan Clemons October 9, 2019 at 1:16 pm


  • Reply ツliyah October 10, 2019 at 4:41 am

    "chinese yen" yen is japanese LMAO

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