oh hello there I'm at the gym I don't
know why you're here but I'm going to do
some push-ups so you can join me on the
floor if you want now I'm not doing this
just to show off or anything I'm
actually doing this for science okay you
see what happened there my arms move my
shoulders moved my back and stomach
muscles moved my heart pumped blood to
all those different places is pretty
mean ah well it turns out that how we
make and use energy is a lot like sports
or other kinds of exercises can be hard
work and a little bit complicated but if
you do it right it comes 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 your best
friends
[Music]
today I'm talking about the energy in
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 that we
eat specifically from glucose since most
of what we eat ends up as glucose here
is the chemical formula for one molecule
of glucose in order to turn this glucose
into energy we're going to need to add
some oxygen 6 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 of 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 US 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're technically our
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 Welbeck 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 that
episode right here 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 well adenosine
triphosphate is made up of a 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 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 seats 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 ad
or adenosine diphosphate because now
there are just two kids sitting on the
bus seat and 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 a no H pairing that's
called a hydroxide from one of the h2o s
comes over and takes the place of that
third phosphate group and everybody is
much happy 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
so now that you know how ATP is spent
let's see how it is 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 or 30 ATP's but whatever people
are still studying this stuff so let's
stick with that number 38
now cellular respiration isn't something
that just happens all at once glucose is
transformed into ATP's over three
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 the cell is kind of
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 O at
the end of it and I call this this is
just the breaking up of glucose is six
carbon ring into two 3-carbon molecules
called pyruvic acids or pyruvate
molecules now in order to explain
exactly how glycolysis works I need
about an hour of your time and a giant
cast of finger puppets each playing a
different enzyme and though it would
paid me to do it I would have to use
words like phospho glucose omurice but a
simple way of explaining it is like this
if you want to make some money
you got to spend some money glycolysis
needs the investment of two ATP's in
order to work and in the end it
generates for ATP s4 in that profit if
you will of two ATP's
in addition to those four ATP's
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 na
Plus pairing with energized electrons
and a hydrogen to create storehouses of
energy that will later be tapped to make
ATP help us keep track of all the
awesome stuff we're making here let's
let's keep score 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 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 gets rerouted into a process
called fermentation if there's no oxygen
in the cell it needs more of that nad
plus to keep the glycolysis going so
fermentation frees up some nad Plus
which happens to create some interesting
byproducts for instance and some
organisms like yeast 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 to follow 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 tissues ah ah ah back to the
score now we have made two molecules of
ATP through glycolysis but yourselves
really need the oxygen in order to make
the other 30 sub molecules that they
need and that is 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 and so we find
ourselves at the next step in cellular
respiration
after glycolysis comes the Krebs cycle
so wild-like Ollis occurs in the
cytoplasm where the fluid medium within
the cell that all the organelles hang
out and the Krebs cycle happens across
the inner membrane of the mitochondria
which are generally considered the power
centers of
the south the krebs cycle takes the
products of glycolysis 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 first while the pyruvate is
oxidized which basically means that it's
combined with oxygen 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 co a
then another nad plus comes along picks
up a hydrogen and becomes NADH
so our two pyruvates create another two
molecules of NADH to be used late as in
glycolysis and really all life enzymes
are essential here 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
these enzymes for example bring together
a phosphate with an ATP to create
another ATP molecule for each pyruvate
enzymes also help join the acetyl co a
and a four carbon molecule called
oxaloacetic acid I think that's how you
pronounce it together and they form a
six carbon molecule called citric acid
and I'm certain that that's how you
pronounce that one cuz yeah it'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
by-product however it is usually
referred to by the name of the man who
figured it all out
Harden's 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
for 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
exhaling the products of the krebs cycle
right now good work
this video by the way using a lot of ATP
making it now each type of carbon comes
off of the citric acid some energy is
made but it's not ATP it's stored and a
whole different kind of molecular
package this is where we go back to NAD+
and it's sort of colleague FA D
NAD+ and FA Dr 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 and the electron
transport chain in fact they're so good
at it that they show up in a lot in
those high-energy vitamin powders that
the kids are taking these days na DS and
fadli quatre e's 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 yields three
NADH s and one fadh2 per cycle and since
each glucose has been broken down into
two pyruvates that means that each
glucose molecule can produce six nadhs
and to fadh2 s the main purpose of the
krebs cycle is to make these powerhouses
for the next and final step the electron
transport chain now comes the time when
you're saying sweet pyruvate sandwiches
Hank aren't we supposed to be making ATP
here let's make it happen Cap'n what's
the holdup well friends your patience is
finally paying off because when it comes
to ATP's the electron transport chain is
the real moneymaker in a very efficient
cell it can net a whopping 34 ATP's so
remember all those nadh and fadh2 s that
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 man
brain 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 ten
NADH s that come out of the krebs cycle
have just enough energy to produce
roughly three ATP's and we can't forget
our friends the fadh2 s we have two of
them and they make two ATP's each and
voila that is how animal cells the world
over make ATP through cellular
respiration now just a check let's reset
our ATP counter and do the math for a
single glucose molecule
once again we made two ATP's for each
pyruvate during glycolysis we made two
during the Krebs cycle and then during
the electron transport chain we made
about 34 and that is 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 watch any parts of this
episode you didn't quite get I really
want to do this quickly because I'm
getting very tired if you want to ask us
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