The Effect of Changing the Concentration of an Enzyme on an enzyme catalysed reaction

[raid517]

Hi I have to do a biology write up and it seems to be going OK so far. The title of the essay is "The Effect of Changing the Concentration of an Enzyme on the Rate of an Enzyme Catalysed Reaction". Obviously in this case, the increased concentration of enzyme results in an increased rate of reaction, up to a given point, when finally all of the active sites of the enzyme are used up. However the question that occurred to me (and one not asked in the essay) is what would happen if you just kept adding more substrate and simply replenished the substrate as it was used up? In other words, would the enzymes continue to work indefinitely? Would they never stop working? And if they did stop working, at what point would this be and why?

[Greippi]

I assume you have a graph featuring a line that starts off as you increase substrate concentration by going up, then curves off until it plateaus. Where the plateau is is where the reaction is going its fastest - the enzyme simply does not "work" any faster no matter how much more substrate you add.

 

I think you might be missing the point of what is happening here. The substrate diffuses in to the active site, the reaction occurs, and the product diffuses out of the active site, leaving the active site free to bind another substrate molecule and catalyse the reaction again.

 

Okay, say you have 10 enzymes. You have 10 active sites available, therefore only 10 molecules of substrate can fit in to the active sites at any one time.

You put in 1 molecule of substrate, there are many active sites available so it quickly binds to the enzyme and the reaction is catalysed, the product diffuses out of the active site which is then free to bind another substrate and do the same thing. You put in more substrate molecules and the rate of reaction increases as more product can be made in the set amount of time as there's more substrate available. But then if you add 11 molecules of substrate at once - all 10 sites get filled up and the 11th molecule has to wait its turn. Increasing the substrate concentration further has no effect on speeding things up as ther's no room in the active sites - they have to wait until the site becomes available.

 

An enzyme can only work so fast and the rate of reaction is different for different enzymes (put simply, there's the speed at which the substrate binds to the active site, the time taken to catalyse the reaction, and the speed at which the product moves out of the active site making it free to bind more substrate).

[CharonY]

As most are equlibrium reactions, you would also to have to remove the product from the system, otherwise upon reaching equilibrium no further net reaction is going to happen. Otherwise it depends on the stability of the protein on how long it can continue working.