ATP and ADP?

S

SheRa329

Cathlete
Hey everyone!! I haven't been checking in very much lately 'cause I've been crackin' the books!!! I'm studying for the ACE exam and there's a lot to learn! x( I've hit a point of confusion and I need some clarity from those that know about exercise physiology. I understand what ATP (adenosine triphosphate)is and how it's made in the body, etc. But one of my friends confused me b/c she started asking me what the difference is b/w it and ADP. I haven't studied ADP yet and she kind of confused me. Can anyone help?? Thanks alot in advance!!!!:) :) Gotta go study some more......:7
 
Well I'm going to go out on a limb here with what I remember (from studying for my ACE and other reading). ATP is tri-phosphate, ADP is di-phosphate. The energy is produced when the tri gives off one phosphate and is therefore converted into di. I think that's right. Does that make sense?
 
ADP is just adenosine diphosphate, the same molecule as ATP before it gets another phosphate transferred to it, so it is "charged" and ready to provide cellular metabolic energy. When the ATP molecule "gives" its energy, it goes back to being ADP. It's been a while since I took a biology class, but this is what I remember.

If I'm wrong, I'm sure someone will correct me.

Liane
 
Great answers and a trip down memory lane for a Biology major! LOL!
I always thought of Adenosine Triphosphate as a charged battery and after it gives off the Phosphate it is then an uncharged battery. That made it easy to picture it.
Just to add to this, in ATP the bond between the second phosphate group and the third phosphate group is the highest average bond energy in the molecule. The bond between the first and second phosphate groups is of slightly lower energy. When the Phosphate is released from ATP it's a hydrolysis reaction: ATP +H2O=ADP +inorganic phosphate. ADP can also be broken down further to produce Adenosine Monophosphate(AMP). There are several methods for the cell to regenerate back to ATP.
Another thing that always intrigued me is the fact that the bond energy when the third phosphate is let go is only about 7 kilocalories per mole. In the big scheme of things, that is VERY low energy. I believe the O-H bond in water is over 100! Or in that neighborhood. Now that everyone is asleep I will end this thread!! LOL!!
Trevor :)
 
Thanks for clarifying, but I'm still confused about something. My friend was saying that ADP is a by-product that's produced when ATP is used, kind of like lactic acid--which could make sense if "using it up" means using one phosphate molecule. Is it then (in ADP form)taken away from the muscle cells by the blood and disposed of? Or is my friend just way off? I wish I wouldn't have slept through all of those hs and college biology classes!!! This is wearing out my brain!!x( x(
 
No, its not disposed of. It is needed for the generation of ATP. ATP is converted to ADP and energy is liberated. ADP can be converted back to ATP by adding a phosphate to ATP. Homeostatsis is maintained by balancing levels of ADP and ATP depending upon the energy requirements of the cell. ADP is also important for other enzymatic reactions and not just conversion to ATP.
 
If you tell me you still have the Krebs cycle memorized I will be impressed beyond words ...

Carol
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