Thursday, November 09, 2006

Oversimplification breeds misconceptions

For all students who've done biology and chemistry at O lvls and Alvls, have you ever wondered about this: in biology you are taught that ATP is a high energy molecule, when its phosphoester link is hydrolysed ie ATP -> ADP + Pi (inorganic phosphate) energy is released.

Yet in chemistry you are taught that bond breaking (as happens during hydrolysis), REQUIRES energy? So which is correct? why the apparent contradiction?


This really stems from the oversimplification of the hydrolysis process taught in bio.
1) the so called inorganic phosphate is simply the phosphate PO4^3- ion or the hydrogen phosphate HPO4^2- ion. (they in equilibrium under cellular pH conditions)

2) ATP and ADP do not exist as neutral molecules either, their phosphate groups are deprotonated and so ATP and ADP are anionic.

Rewrite the eqn ATP^4-(aq) -> ADP^2-(aq) + HPO4^2-(aq)

The key difference is something as minor as the (aq)!
The P-O bond in the phosphoester link is actually quite weak so it requires little energy to hydrolyse (but energy is still required). However after the reaction, you've got TWO ions instead of just one. The phosphate ion is a small ion that forms ion dipole interactions readily with water; ie formation of HYDRATED HPO4^2- ion releases large amounts of energy.
Having two ions instead of one means more energy is release from hydration. and for those who take thermodynamics at higher levels they should also know that the entropy of the system increases.

So overall the reaction releases free energy.

Ther are many other misconceptions actually propogated in sec sch science eg ..octet rule as a driver of reactions in chem.. and in bio some people use the word oxalate for example to refer to oxalic acid, when in fact oxalate is the anion of the acid (after its deprotonated)...

I think simplification is good when it allows you to deal with issues without getting bogged down by too many details. But it should be done accurately and also set in a right context.
Oversimplification of anything, not just science but also in many current affairs issues, philosophy, religion, on the other hand, propogates misconceptions, clouds sound judgement, and mislead people.

Look at the masses of ignorant, misdirected people in this world....myself included

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