How do cells get energy from converting ATP to ADP?

Question

I know a phosphate group is removed, but HOW does this give a cell energy? Please explain as much as you can.

Thnak you,

-David

I gotta think? Damn...

I hope you can too. :-)

Answer 1

I'll take a stab at this in an hour or so. I am busy right now but I hope I can explain it to you. Ok, I'm back. The first thing you must understand is the second law of thermodynamics. This says that all processes that involve the transfer of energy will necessarily proceed in the direction of increased randomness. I visualize this best by imagining that I have an open jar full of tadpoles and I drop it into a pond of water, and when I come back a while later I find that the tadpoles are all over the pond, and no longer in the jar. Furthermore, it would be really tough to get them all back in the jar. Another way of looking at it is trying to put the toothpaste back into the tube. This kind of phenomenon is what drives all chemical reactions in the forward direction.
So when an ATP loses a phosphate, a similar situation is occurring. However, simply losing a phosphate is not helpful or productive by itself. The key is that most enzyme systems are coupled to the ATP/ADP conversion. This ATP/ADP conversion is then the driving force that causes the reaction to proceed in the "correct" direction. There are a few enzyme mediated steps that require even more driving force than ATP/ADP conversion can provide. These are usually coupled to an ATP->AMP conversion, which yields about twice the thermodynamic driving force.
Yet another way of understanding this situation is to imagine that you have a gold mine at the bottom of a deep hole. The gold is useless unless you can bring it up out of the mine. So you set up a teeter-totter arangement, and place a bag of gold on the downside of the teeter-totter. How do you get the gold to come up out of the mine? You place a bag of ordinary rocks on the upside of the teeter-totter, and if it is heavier than the bag of gold, then the gold will come up and the bag of rocks will go down. This is how an enzyme reaction coupled to ATP/ADP conversion works. As the ATP is "destroyed", the other coupled reaction is "driven". One side will not work without the other side also happening, just as the gold will not come up out of the mine unless you put a weight of greater size onto the other side of the teeter-totter. I hope this helps.

Answer 2

David,
ATP itself, as a molecule, is pretty unfavorable. it has 3 phosphate groups all right next to each other, all 3 with negative charges that are repelling each other.
ADP and Pi are pretty favorable in comparison. ADP only has 2 phosphates, meaning less negative charges to repel each other. and Pi goes into solution pretty easily too.
so ATP is a "high energy" molecule and ADP is a lower energy molecule. therefore turning ATP into ADP will release this energy.
ok well, if this is so then how can ATP last in the cell? why doesn't it just spontaneously break into ADP?
because of the energy of activation needed to break ATP apart. an enzyme is needed before ATP can be broken, and with this enzyme we can conserve some of the energy released by ATP to ADP and use it to make some other high energy bond that we need!
hope that helps!

hi, I just read what Bauercvhs said and wanted to clarify some things.
ATP is a VERY stable, which is why it is such a good universal energy source. if it were unstable it would just break down randomly and we wouldn't be able to use its energy to drive another reaction we wanted to happen.
also, ATP isn't easy to make. that's an entirely different story but if you want to get involved check out oxidative phosphorylation.
sorry if this is such a confusing topic!

Answer 3

All these people are not answering your question.

The ATP molecule is actually a very unstable molecule with weak phosphate bonds. Weak bonds are actually high energy bonds. "Weak" just means they break easy. Since they are "weak" and unstable, not much energy is needed to make them. but this also makes them easy to break and release their energy.

Often cells need to change molecules by breaking some bonds and making others. Sometimes the new bonds are of higher energy. Sometimes they are of lesser energy, but still a certain amount of "activation energy" is needed get the change to occur (like striking a match). When the last phosphate is taken off ATP it is transferred to a molecule of interest, the bond is transferred as well. Later when an enzyme comes across this molecule, it removes this phosphate and can take some of the energy in that bond to break and/or make other new bonds within the molecule.

Answer 4

It turns out that the phosphate bound is one of the thighest bounds in the nature. So, when your cells manage to break one down, a lot of energy is released, like some kind of explosion that can be used to a lot of processes in the metabolism.

Answer 5

That is a easy bond to make, but when sundered, much energy is released. Think of powerful chemical explosions, as opposed to a mere rapid burning reaction. The disassociation of ionic bonds vs. covalent bonds.

Answer 6

I guess you didn't do very well on your Biology final...The correct answer is organic molecules (like sugar)...The question is asking about animal cells, not plant cells...