In the presence of the enzyme alcohol dehydrogenase, the rate of reduction of acetaldehyde to ethanol increases as you increase the concentration of the substrate, acetaldehyde. Eventually the rate of the reaction reaches a maximum, where further increases in the concentration of the substrate has no affect on the reaction rate. This kind of event is common to many enzymatic reactions.
Can you please explain in detail what is happening here, so I can better understand it?
Pretend you have only 1 molecule of enzyme (alcohol dehydrogenase, ADH) in a tube. You add a little bit of substrate (acetaldehyde). The enzyme will convert the acetaldehyde into ethanol as fast as it can. Now, repeat the experiment with a little bit more acetaldehyde in the tube. The 1 molecule of ADH present will do its best to convert the substrate into product. In so doing, the enzyme is getting more activity. We call this "enzyme activity." ...