Which graph depicts the rate of an enzyme-catalyzed reaction from low substrate concentrations to saturating substrate concentrations?

Question

I am a little confused on what substrate means exactly... so in turn I am not exactly sure what the question is asking.

I know the answer is C and I would like to know why. Also, what would the other graphs describe or show exactly?


Since I cannot recreate these graphs on WyzAnt, I had to take a picture of the problem and post it on another website.

http://s1195.photobucket.com/user/BirdySweet/media/IMG_6749_zpsckzwumty.jpg.html?filters[user]=122455705&filters[recent]=1&sort=1&o=0

Answer 1

Basically enzymes function as catalysts. A catalyst what ever the kind, combines with a reactant to "activate" it.  In the case of enzyme-catalysts, the reactant or reactants are generally referred to as substrates. the activated complex undergoes a chemical change to form products and regenerate the enzyme.

 

     E         +     S         >>>       E-S          >>>>>      E        +      P

 

enzyme        substrate       enzyme-substrate          enzyme         product

                                          complex

 

Graph C depicts the rate of an enzyme-catalyzed reaction dependent of the quantity of the substrate (reactants)

The Y-axis represents the velocity of the reaction

The x-axis represents the concentration of the substrate or reactants.

 

So, as the concentration of the substrate increases (to the right), the velocity of the reaction increases as well (going up), but there is a time when there is so much substrate that all the enzymes are working on catalyzing the conversion of substrate to product and have reached their max velocity. At this point, the velocity does not change and we say that the enzyme is saturated.

 

Graph A

shows the concentration of an enzyme itself. Increasing the concentration of the enzyme, increases the rate of conversion of substrate to product. in this case X-axis represents the [E] the concentration of the enzyme

the Y-axis, the velocity of the reaction.

 

Graph D

It represents the catalytic activity of an enzyme as a function of pH. Most enzymes have a catalytic activity in the pH range 4 to 8. However some enzymes(like Pepsin) have maximum activity outside this range. Therefore, the catalytic activity of most enzymes falls off rapidly at pH values on either side of their particular pH maximum.

 

Graph B

If we start with the premise that all graphs have to do with enzyme activity, we could explain this graph as depicting the decrease in enzymatic activity as the substrate continues to increase. there is so much substrate that the enzyme cannot catalyze it all. therefore, the velocity decreases fast.

 

I hope it helps !