Biology VS Chemistry

[soonny]

In chemistry, the breaking of bonds are always classified as endothermic reactions. However, biology explains the conversion of Adenosine Triphosphate (ATP) to Adenosine Diphosphate (ADP) which involves the breaking of bonds to be an exogernic reaction realeasing energy to the environment instead of absorbing it. Why and how?

[Blender]

I don't know the reason why but I reckon that the release of heat is exothermic

[Hippy]

You might mean "exogenous" meaning caused by an external force, or more litererally outside the organism.

[soonny]

No... what I meant was ATP + H2O --------> ADP + P + H This reaction is Exergonic, which means energy is released...

[Hamish]

In most reactions, especially in a biological environment, bonds are both broken and formed. The key to getting energy out of the system is to form stronger bonds than the ones you broke, this is certainly the case in the ATP --->ADP case you are talking about.

For example:

1/2 O₂+H₂ ----> H₂O

The Oxygen molecule had a bon energy of 498kJ per mole, as we have 0.5 of a mole we use 249 kJ per mole to break the bond. For the hydrogen molecule the energy is 436kJ per mole. Therefore the total energy to break the bonds is 685 kJ per mole. The water molecule has two O-H bonds each with a bond energy of 427.6kJ per mole, total energy 855.2kJ per mole.

The energy released is therefore 855.2-685 = 170.2kJ per mole. So even though we broke some bonds the formation of the new bonds gives out more energy that the was used up in breaking the bonds in the first place. This is basic thermodynamics. There are some cases where other factors have to be considered, but I don't think that the ATP--->ADP will be one of them. Hope this helps, Hamish

[soonny]

Does the enzyme action (ATPase) have anything to do with the energy evolved?

[Hamish]

I would suggest that there is a bond formed between the lost phosphate and the enzyme. Hamish

[soonny]

wow... that means the the enzyme would have been phosphorylated and therefore very much denatured! Are you suggesting that the phosphate released are non-competitive inhibitors?

[Hamish]

I'm a chemist not a biologist (I only know the basics of the ATP----->ADP process), so to answer that I'll have to do a bit more reading, but biology aside the laws of thermodynamics cannot be broken. If you can get some more info on the ATP ----> ADP process then that would help.

[soonny]

"the laws of thermodynamics cannot be broken" Well I'm glad to hear that from a chemist! I'll do more reading on that topic and I'll let you know if I've discovered anything, that is if you're interested in biology facts... thanks!

[emyradams]

ATPase will act to lower the energy required to remove a phosphate group from ATP. However this will not involve the change of ATPase at the end of the reaction process. ATPase is an enzyme catalyst and so will not change overall. It is unlikely that phosphate will act as a non-competitive inhibitor as it will be a very reactive species.

[Hamish]

Hi I've done a little searching on the net. It appears that ATPase does indeed form a bond with ATP via a Mg-O group. There is a whole load of stuff here
emyradams, target=_blank>http://www.bris.ac.uk/Depts/Chemistry/MOTM/atp/atp
1.htm

emyradams, the bond will be weak, but necessary. Enzymes need to form bonds (even hydrogen bonds) to hold a molecule in place, they work by bringing to molecules into close proximity so that they can react. This principle is similar to, but far mor complicated than, the formation of ammonia by the Born Harbour process.

hope this helps. It look like Soonny has a lot of reading ahead if they're to get to the bottom of this!

[Andromeda]

Soonny, remember that an enzyme can never increase or reduce the amount of energy released in a reaction. It only makes it occur more easily. Enzymes should never actually be chemically altered by the reaction, but they do form weak bonds, depending on the type of enzyme. That is how they are able to alter the reaction conditions.

Andy

[emyradams]

Apologies, I didn't really make myself clear. Enzymes will form weak attractions to the species involved in the reaction but what I meant was that these are only very temporary reactions. The energy involved in the change from ATP to ADP is more concerned with the hydrolysis of the bond and not the breaking of bonds and not the bond energies (although bonds are formed and broken). I think one of the crucial differences between chemical systems and biochemical environments is that in the latter reactions are not really occurring in isolation, there are many many reactions occurring simultaneously or in sequence. ATP is the "energy currency" of most living organisms. It is the hydrolysis of the phospoester bonds to give more stable species that allows energy to be released which feeds further reactions. ATPases are involved in hydrolysing ATP to give sufficient energy to transport species across plasma membranes against concentration gradients.

[soonny]

wow... thanks ya'll. :) Hamish is correct... I do have a lot of reading to do.