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Sal: ATP or adenosine triposphate
is often referred to as
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the currency of energy, or
the energy store, adenosine,
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the energy store in biological systems.
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What I want to do in this video is get
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a better appreciation of why that is.
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Adenosine triposphate.
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At first this seems like
a fairly complicated term,
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adenosine triphosphate, and
even when we look at its
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molecular structure it seems
quite involved, but if we break
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it down into its constituent
parts it becomes a little bit
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more understandable and we'll
begin to appreciate why,
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how it is a store of energy
in biological systems.
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The first part is to break
down this molecule between
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the part that is adenosine
and the part that
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is the triphosphates, or
the three phosphoryl groups.
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The adenosine is this
part of the molecule,
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let me do it in that same color.
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This part right over here is adenosine,
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and it's an adenine connected to a ribose
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right over there, that's
the adenosine part.
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And then you have three phosphoryl groups,
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and when they break off they
can turn into a phosphate.
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The triphosphate part
you have, triphosphate,
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you have one phosphoryl
group, two phosphoryl groups,
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two phosphoryl groups and
three phosphoryl groups.
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One way that you can conceptualize
this molecule which will
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make it a little bit easier
to understand how it's a store
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of energy in biological systems
is to represent this whole
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adenosine group, let's just
represent that as an A.
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Actually let's make that an Ad.
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Then let's just show it bonded to
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the three phosphoryl groups.
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I'll make those with a P
and a circle around it.
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You can do it like that,
or sometimes you'll see it
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actually depicted, instead
of just drawing these
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straight horizontal lines
you'll see it depicted
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with essentially higher energy bonds.
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You'll see something like that to show
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that these bonds have a lot of energy.
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But I'll just do it this way
for the sake of this video.
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These are high energy bonds.
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What does that mean, what does that
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mean that these are high energy bonds?
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It means that the electrons
in this bond are in a
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high energy state, and if
somehow this bond could be
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broken these electrons are
going to go into a more
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comfortable state, into
a lower energy state.
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As they go from a higher
energy state into a lower, more
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comfortable energy state they
are going to release energy.
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One way to think about it
is if I'm in a plane and
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I'm about to jump out I'm
at a high energy state,
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I have a high potential energy.
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I just have to do a
little thing and I'm going
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to fall through, I'm going to fall down,
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and as I fall down I can release energy.
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There will be friction
with the air, or eventually
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when I hit the ground
that will release energy.
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I can compress a spring
or I can move a turbine,
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or who knows what I can do.
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But then when I'm sitting on my couch
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I'm in a low energy, I'm comfortable.
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It's not obvious how I could
go to a lower energy state.
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I guess I could fall asleep
or something like that.
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These metaphors break down at some point.
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That's one way to think
about what's going on here.
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The electrons in this bond,
if you can give them just
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the right circumstances they
can come out of that bond
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and go into a lower energy
state and release energy.
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One way to think about it, you start
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with ATP, adenosine triphosphate.
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And one possibility, you put
it in the presence of water and
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then hydrolysis will take
place, and what you're going to
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end up with is one of these things
are going to be essentially,
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one of these phosphoryl
groups are going to be
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popped off and turn into
a phosphate molecule.
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You're going to have
adenosine, since you don't
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have three phosphoryl
groups anymore, you're only
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going to have two phosphoryl
groups, you're going to
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have adenosine diphosphate,
often known as ADP.
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Let me write this down.
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This is ATP, this is ATP right over here.
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And this right over
here is ADP, di for two,
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two phosphoryl groups,
adenosine diphosphate.
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Then this one got plucked
off, this one gets plucked
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off or it pops off and it's
now bonded to the oxygen
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and one of the hydrogens
from the water molecule.
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Then you can have another hydrogen proton.
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The really important part of
this I have not drawn yet,
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the really important part of it,
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as the electrons in this
bond right over here go into
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a lower energy state they
are going to release energy.
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So plus, plus energy.
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Here, this side of the reaction,
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energy released, energy released.
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And this side of the interaction
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you see energy, energy stored.
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As you study biochemistry
you will see time and time
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again energy being used in
order to go from ADP and
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a phosphate to ADP, so
that stores the energy.
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You'll see that in things
like photosynthesis
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where you use light energy to essentially,
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eventually get to a point
where this P is put back on,
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using energy putting this P
back on to the ADP to get ATP.
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Then you'll see when biological
systems need to use energy
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that they'll use the ATP
and essentially hydrolysis
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will take place and they'll
release that energy.
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Sometimes that energy could
be used just to generate heat,
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and sometimes it can be
used to actually forward
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some other reaction or
change the confirmation of
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a protein somehow,
whatever might be the case.