Analysis of enzyme reaction graph Flashcards
Enzyme activity is measured by concentration of the ________ and/or the ________.
substrate; product
In the graph, line A represents the concentration of substrate, while line B represents the formation of product over time.
Why does the line for Substrate decrease and the line for Product increase over time?
Because the enzyme converts the substrate to product, so as substrate decreases, product increases.
The Michaelis-Menten Graph and it shows several important features of the enzyme. What is the most important one?
How fast the Product is formed at increasing levels of Substrate Concentration
What is happening in this Michaelis-Menten Graph?
At first, as substrate concentration increases, the rate of catalysis increases. When the graph approaches the dashed line the graph levels off.
The graph levels off because the enzyme is saturated with substrate. There are no more active sites available to perform catalysis so the enzyme cannot work any faster.
Define Enzyme-substrate affinity. What is its relationship to Km?
Enzyme-substrate affinity is the tendency for enzyme and substrate to bind together and form the enzyme substrate complex.
It is convenient to use Km as a measure of the affinity between the enzyme and substrate: this is an inverse relationship.
The Michaelis-Menten Graph also shows the theoretical maximum rate of the enzyme (Vmax), the point where the enzyme is working at ½ its maximum rate (Vmax/2), and amount of substrate needed to bind half of the active sites (Km).
Label these points on the graph.
Vmax represents: The maximum rate of catalysis, the point where the enzyme is saturated with substrate and has not more active sites available.
Vmax/2 represents: ½ the maximum rate of catalysis, the point where ½ the active sites are available.
Km represents: The substrate concentration level needed to fill ½ the active sites of the enzyme in the reaction pool.
This graph compares two different enzymes with different enzyme kinetics.
Does the graph have any of the same values for their Vmax, Vmax/2 or Km? If so which are the same and which are different?
They have the same Vmax and Vmax/2, but the Km is different.
Enzymes with high affinity for their substrate will readily ___________. Therefore they will need a ______ substrate concentration to reach Vmax/2 and will have a _____ Km.
form the enzyme substrate complex
Low substrate concentration
Low Km
Enzymes with a low affinity for the substrate will ________. Therefore they will need a _________ to reach Vmax/2 and will have a _____ Km.
not readily form the enzyme substrate complex
high substrate concentration
Have high Km
How does a competitive inhibitor change a Michaelis Menten Graph?
At a relatively low substrate concentration, the rate of the reaction will be less in the presence of a competitive inhibitor.
As the substrate concentration increases, the substrate out-competes the inhibitor.
If there is a lot more substrate than inhibitor, the chances are far higher that a substrate will bind to the active site than an inhibitor will.
What is a competitive inhibitor is and how does it interact with the enzyme?
A competitive inhibitor is a molecule that competes with the substrate for binding to the active site of the enzyme.
Look at the graph of how a competitive inhibitor affects the kinetics of an enzyme:
Is the Vmax of the enzyme affected? Why or why not: explain in terms of substrate concentration and enzyme active site saturation.
Is Vmax/2 affected? Why or why not: explain in terms of Vmax.
Vmax is not affected; this is because eventually the amount of substrate will completely overwhelm the enzyme and the competitive inhibitor.
Vmax/2 is not affected because Vmax is not affected.
Look at the graph of how a competitive inhibitor affects the kinetics of an enzyme: Is Km affected? Explain in terms of the active site.
Yes, Km is affected because the Competitive Inhibitor (C.I.) is competing for binding to the active site so there is an apparent shift in the enzymes affinity for the substrate (Km is higher on the graph).
- the enzyme has the option to bind the substrate or the C.I. so it will take a higher substrate concentration to bind to ½ active sites.
Definea noncompetitive inhibitor is and how it interacts with the enzyme.
A noncompetitive inhibitor will bind to any location on the enzyme or the enzyme substrate complex (except the active site) and slow the enzyme down.
How does a noncompetitive inhibitor change a Michaeli-Menten Graph?
Once a noncompetitive inhibitor has bound to the enzyme, that particular enzyme won’t work any more.
Even if binding with noncompetitive inhibitor is reversible, there will be a proportion of the enzyme that is out of action at any one time.
The new Vmax will be lower than the one where there was no inhibitor present. No matter how much you increase the concentration of the substrate, you will never reach the original Vmax.
