Enzyme concentration Vs substrate concetration.

[k-dog]

Hi.

As far as how substrate concentration effects rate of reaction, I understand that with a fixed number of enzymes the rate of reaction will eventually flat line when you increase substrate concentration due to the enzyme active sites being full. However I don't understand why the reverse of this doesn't apply when you increase the number of enzymes. Shouldn't the enzymes run out of substrates to attach to? The only way I can see this working is if It is implied that there are infinite reserves of substrates when asking about the affect of enzyme concentration.

Im probably failing to see something obvious, please help me out!

[Yacoubb]

I believe that when you increase enzymes, no matter how many you add, will result in the same product made. However, the time taken for product to be manufactured from the catabolism/anabolism of the substrate will decrease because there are more enzymes to do the job quicker.

Analogy - you build a road. You want to build a 1km road. No matter how many workers there are, you will have 1km made. But the process of building the road becomes quicker when there are more workers to do the job!

[k-dog]

Okay, But if you have, say, 2 substrates and you continuously add enzymes, Surely there will be no increase in reaction rate? When I look at your anology I think of a situation where there are so many workers that there is no more space on the road to work, so the increase in the  rate of reaction slows down.

[Yacoubb]

Hence if you look at a graph you see the line slowly straightening out and remaining stable.

[Scooby]

There's two graphs that describe the reaction rate of an enzyme-catalysed reaction when we increase enzyme concentration

The first one is just a straight diagonal line that doesn't plateau. We only ever use this graph to describe the effect of increasing enzyme concentration if there are infinitely many substrate molecules available (ie. no matter how high the concentration of enzymes in this solution, we will never run out of substrate)

The second one looks like the graph that we use to describe the effect of increasing substrate concentration. It plateaus. Why does it do that? Well, as a consequence of continually increasing enzyme concentration, we've run out of substrate molecules. We use this graph when there are not infinitely many substrate molecules available (ie. in cases where we will eventually run out of substrate). In VCE Bio, this is the graph you'll use to describe the effect on reaction rate of increasing enzyme concentration

[k-dog]

Thanks scooby, It makes so much more sense if there is an infinite supply of substrate.