Thread: when chemistry meets biology

well this will be related to both chemistry and biology

what i know about chemistry-
breaking bonds is an endothermic reaction
building up bonds is an exothermic reaction

what i learnt from biology- ADP and ATP
(well, can i assume the people here know about ADP and ATP?)
to attach a Pi to ADP requires energy
to detach a Pi from ATP to form an ADP gives out energy

is there a contradiction between chemistry and biology or i took any of them wrongly?

8)

No there is no contradiction. The problem is in A level biology (or the equivalent where you live) you are only told the simplified version of the reaction.

When ADP is formed from ATP, it involves breaking a bond to give yield the free phosphate, which like you said, costs energy. However the phosphate released will quickly react with one of three amino acids with a hydroxyl group (serine, threonine and tyrosine) which is why you talk about the hydrolysis of ATP. As the new bond formed is covalent, it has a higher bond enthalpy value than the original bond broken, therefore the overall reaction is exothermic. Hope that makes sense.

yes! thanks
i was just expecting some other unknown reaction that may be an exothermic reaction requires higher energy.