How does an enzyme increase the speed of a chemical reaction?

Answer 1

Enzymes can increase the speed of chemical reactions in several ways. I will explain one in detail (the most common one) and just mention another that I can think of.

Most often, they lower what is called the activation energy of a chemical transformation. Think of it this way- you have a Bowling ball that is sitting half way up on the side of a mountain. You want to push the bowling ball up over the peak and let it roll down to the bottom of the other side. In order to do that, you have to put energy in to roll the ball all the way to the top, before it can roll down the other side.

This is an analogy for activation energy. A chemical reaction is a change in chemical state from a higher energy state (1/2 way up the mountain) to a lower energy state ( at the bottom on the other side). But, this doesn't happen spontaneously. Match heads don't just ignite on their own, and logs don't burst into flame. You have to put IN some energy before it can do down to its lower energy state (you have to push the ball UP some before it can roll to the bottom).

With that out of the way, we can get back to how the enzyme works. It LOWERS the needed activation energy. In our analogy, the enzyme would chop off the top of the mountain altogether, so we did not need to push the bowling ball as high before it could roll to the other side.

Now to get technical. When molecules combine, there is what is called an intermediate state. It is usually an unstable shape, and only present for an instant when the 2 molecules first join. Since it is an unstable and unfavorable state, it requires an input of energy to happen at all. This is why there is a hump to go over in our analogy. The active site of many enzymes is in the exact shape (only opposite) of this intermediate. You can think of the enzyme's active site as a sort of mold, where the 2 molecules come in, and it is much easier for them to join, form the intermediate, and end up in a more stable conformation. If they tried to join outside of the enzyme, it would require more energy input, because that intermediate state is not stabilized.

Enzymes can also form micro environments. For example, if a reaction needs to be in acid to occur, an enzyme can have a tiny micro environment that is acidic, in order for the reaction to happen as it needs to.

Answer 2

Enzymes increase the rate of reactions in several ways. Enzymes may increase the rate of chemical reactions by decreasing the activation energy, Ea, of the reaction. Ea is measured as the difference in energy between the energy of the transition state and the energy of the reactants. Activation energy and rate is related by the Arrhenius Equation: k = Ae-Ea/RT, where k, the reaction rate constant at a given temperature T is inversely related to Ea (R and A are constants), i.e. the lower the Ea, the higher the reaction rate constant, k. Activation energy is decreased by purposeful straining of bonds in the substrate with polar/ionic groups in the enzyme so as to favour the transition state structure over the original structure (i.e. decrease the energy of the transition state). Many enzymes may also simply provide an alternative pathway of reaction, for example allowing the formation of an substrate-enzyme complex so that future reactions can proceed with this complex. Enzymes may also function by simply holding the reactants in an orientation that favours reaction. Recall that reactants have to collide in a specific orientation (low probability) for the reaction to occur, and holding the reactants in such an orientation increases the probability of reaction. These previous mechanisms decrease the ΔG of the reaction, making it more favourable. Recall ΔG = -RTlnK, and lowered ΔG makes the equilibrium (most enzymic reactions are equilibrium reactions) lie further to the right (products), i.e. higher K. One final mechanism is that enzymes make add another group (e.g. phosphate from ATP) to its substrate and this new group modifies the electron density in the substrate in such a way so as to increase the reactivity of the substrate in future reactions.

Answer 3

The enzyme reduces the activation energy of the reaction, therefore chemical reaction speeds are increased.

Answer 4

Enzymes speed up the rate of chemical reactions by lowering the energy of activation (the amount of energy needed to begin a reaction).

Answer 5

read and you will find out

Answer 6

Something about intermediate attraction