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  • Sal: ATP or adenosine triposphate is often referred to as

  • the currency of energy, or the energy store, adenosine,

  • the energy store in biological systems.

  • What I want to do in this video is get

  • a better appreciation of why that is.

  • Adenosine triposphate.

  • At first this seems like a fairly complicated term,

  • adenosine triphosphate, and even when we look at its

  • molecular structure it seems quite involved, but if we break

  • it down into its constituent parts it becomes a little bit

  • more understandable and we'll begin to appreciate why,

  • how it is a store of energy in biological systems.

  • The first part is to break down this molecule between

  • the part that is adenosine and the part that

  • is the triphosphates, or the three phosphoryl groups.

  • The adenosine is this part of the molecule,

  • let me do it in that same color.

  • This part right over here is adenosine,

  • and it's an adenine connected to a ribose

  • right over there, that's the adenosine part.

  • And then you have three phosphoryl groups,

  • and when they break off they can turn into a phosphate.

  • The triphosphate part you have, triphosphate,

  • you have one phosphoryl group, two phosphoryl groups,

  • two phosphoryl groups and three phosphoryl groups.

  • One way that you can conceptualize this molecule which will

  • make it a little bit easier to understand how it's a store

  • of energy in biological systems is to represent this whole

  • adenosine group, let's just represent that as an A.

  • Actually let's make that an Ad.

  • Then let's just show it bonded to

  • the three phosphoryl groups.

  • I'll make those with a P and a circle around it.

  • You can do it like that, or sometimes you'll see it

  • actually depicted, instead of just drawing these

  • straight horizontal lines you'll see it depicted

  • with essentially higher energy bonds.

  • You'll see something like that to show

  • that these bonds have a lot of energy.

  • But I'll just do it this way for the sake of this video.

  • These are high energy bonds.

  • What does that mean, what does that

  • mean that these are high energy bonds?

  • It means that the electrons in this bond are in a

  • high energy state, and if somehow this bond could be

  • broken these electrons are going to go into a more

  • comfortable state, into a lower energy state.

  • As they go from a higher energy state into a lower, more

  • comfortable energy state they are going to release energy.

  • One way to think about it is if I'm in a plane and

  • I'm about to jump out I'm at a high energy state,

  • I have a high potential energy.

  • I just have to do a little thing and I'm going

  • to fall through, I'm going to fall down,

  • and as I fall down I can release energy.

  • There will be friction with the air, or eventually

  • when I hit the ground that will release energy.

  • I can compress a spring or I can move a turbine,

  • or who knows what I can do.

  • But then when I'm sitting on my couch

  • I'm in a low energy, I'm comfortable.

  • It's not obvious how I could go to a lower energy state.

  • I guess I could fall asleep or something like that.

  • These metaphors break down at some point.

  • That's one way to think about what's going on here.

  • The electrons in this bond, if you can give them just

  • the right circumstances they can come out of that bond

  • and go into a lower energy state and release energy.

  • One way to think about it, you start

  • with ATP, adenosine triphosphate.

  • And one possibility, you put it in the presence of water and

  • then hydrolysis will take place, and what you're going to

  • end up with is one of these things are going to be essentially,

  • one of these phosphoryl groups are going to be

  • popped off and turn into a phosphate molecule.

  • You're going to have adenosine, since you don't

  • have three phosphoryl groups anymore, you're only

  • going to have two phosphoryl groups, you're going to

  • have adenosine diphosphate, often known as ADP.

  • Let me write this down.

  • This is ATP, this is ATP right over here.

  • And this right over here is ADP, di for two,

  • two phosphoryl groups, adenosine diphosphate.

  • Then this one got plucked off, this one gets plucked

  • off or it pops off and it's now bonded to the oxygen

  • and one of the hydrogens from the water molecule.

  • Then you can have another hydrogen proton.

  • The really important part of this I have not drawn yet,

  • the really important part of it,

  • as the electrons in this bond right over here go into

  • a lower energy state they are going to release energy.

  • So plus, plus energy.

  • Here, this side of the reaction,

  • energy released, energy released.

  • And this side of the interaction

  • you see energy, energy stored.

  • As you study biochemistry you will see time and time

  • again energy being used in order to go from ADP and

  • a phosphate to ADP, so that stores the energy.

  • You'll see that in things like photosynthesis

  • where you use light energy to essentially,

  • eventually get to a point where this P is put back on,

  • using energy putting this P back on to the ADP to get ATP.

  • Then you'll see when biological systems need to use energy

  • that they'll use the ATP and essentially hydrolysis

  • will take place and they'll release that energy.

  • Sometimes that energy could be used just to generate heat,

  • and sometimes it can be used to actually forward

  • some other reaction or change the confirmation of

  • a protein somehow, whatever might be the case.

Sal: ATP or adenosine triposphate is often referred to as

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