Help, please! We did an experiment on enzymes, and it showed that as substrate concentration went up...?

Question

the rate of enzyme activity (catalyzation) went up. I don't understand this! Do the enzymes work harder when there is more to do?

I would appreciate any explanations, or websites i might find useful. Thanks so much!

Answer 1

http://www.biologymad.com/master.html?http://www.biologymad.com/Enzymes/enzymes.htm

http://www.tvdsb.on.ca/westmin/science/sbi3a1/digest/enzymes.htm

http://www.activescience-gsk.com/miniweb/content/enzymes/how_do.htm

I use these websites with my students...it has some basic enzyme info.

An enzyme is active only when there is substrate present. So therefore, the rate of activity will increase when thre is "something to do!"

Answer 2

An enzyme is not active only when substrate is around !!!
It is basic biochemistry so you can read about it on lots of sites, try wikipedia and google for enzymes and michaelis-menten kinetics.

You should observe in your experiment that as you increase the concentration of substrate the rate of the reaction will increase until you approximate a certain maximal value.
This is because at low substrate concentrations, at a given moment in time, not all of the enzyme molecules will be catalyzing a reaction, simply because there is not that much substrate around. As the substrate concentration increases, more enzyme active sites will be catalyzing a reaction at any given moment, leading to an increase of the reaction rate.
After a certain substrate concentration you reach saturation (all active sites are occupied at all times) and thus the rate of the reaction will have the same (maximal) value regardless of how much further you increase the substrate concentration. As you understand this value of substrate concentration depends also on the amount of enzyme you have in the reaction (for lower enzyme concentration you reach saturation with lower substrate concentrations).

The catalytic activity of the enzyme is the SAME for all substrate concentrations and it is expressed by kcat.
Think of it approximately as a normal reaction, with no catalysis to understand why the enzyme activity is always the same but the rate of the reaction changes; the rate of the reaction increases as you increase the concentration of the reactants but the rate constant (k) is the same regardless of the values of the concentrations.