How exactly do enzymes work ?

[VultureV1]

How do enzymes actually increase the rate of a chemical reaction ? Take ATP Synthase for example , how does it work ? does the rotary motion squish the the inorganic phosphate to adp and make it chemically bond to form atp ? Likely not , Can someone explain to me what exactly happens ? What about the enzyme catalase ? I believe It does not have moving parts . What exactly happens in the active site of catalase ?
Sorry for stuffing in these many questions .

[gabevillegas]

There are many different mechanisms by which enzymes increase reaction rates. However, the one thing they all have in common is that their active sites accommodate the transition state product(s) of the reaction they catalyze. So for example Imagine a hypothetical "enzyme" that catalyzes the breaking of a metal bar. In order to break the bar, you must take the straight bar(substrate), bend it(transition state) and eventually it will break in half (products). So when a straight bar finds itself in the active site of the enzyme, interactions between the bar and the active site will make it energetically favorable to adopt a bent conformation (for an instantaneous amount of time because...). Once in the bent conformation the reaction could proceed either way (returning to straight or breaking in half). But because without the enzyme the bar would never find itself in a bent conformation on its own, this reaction is sped up many orders of magnitude. Most if not all enzymes work in a similar way, by stabalizing the transition state of the reaction they are catalyzing allowing very energetically unfavorable reactions to occur (which speeds up the reation rates).

[Titan1290]

Everything said above is good, I just wanted to add for ATP synthase there is 3 conformations: open, loose and tight these are examples of conformational changes and usually occur when the reactant comes in contact with the active site. You can read through it here and see a nice picture. http://en.wikipedia.org/wiki/ATP_synthase This increases reaction rate because there is more chance of the reactants coming together to react and form the product. As you said it's not squishing the protein it's about increasing the chance that they will come together. In one of the laboratories I did to investigate oxygen utilisation and ATP formation. The reaction rate increased by adding ADP to ATP synthase (mitochondrial cells) this was because of the higher concentration of ADP and also because this increased chance of ADP coming in contact with ATP synthase enzyme. Also another way to prove this is by adding a competitive inhibitor. If you add a competitive inhibitor to the reaction you will notice the reaction rate will decrease. This is because the competitive inhibitor is competing for the active site as I said before it's all about the probablilty/chance of the reaction to happen.