Enzyme Kinetics Flashcards
Factors (4) that affect enzyme kinetics
Temperature, pH, presence of activators/inhibitors, substrate
What effect does pH have on a protein?
pH affects protonation/deprotonation of an active site and can lead to denaturation in extremes.
What is the optimal temperature for enzyme activity?
37 degrees Celsius
As temperature increases by 10 degree increments toward 37 degrees Celsius, the enzyme’s activity increases by ___.
2x
Why is transition state energy important for enzyme-substrate binding?
Transition state energy is used for the enzyme to complete its rxn
Why do enzymes have no effect on the Keq ([P]/[S])?
Enzymes are released at the end of the reaction. Enzymes “cancel out” at the end of the reaction.
In a zero order reaction, the substrate is ____ so the reaction is dependent on concentration of___.
saturated, enzyme
First order reactions are dependent on ____ concentration.
substrate
Second order reactions are often treated as ___-___ ___ reactions because the amount of one of the ____ is kept very high.
pseudo-first order, substrates
E.g. think of water being in high concentration. We ignore water when it is one of the substrates because the reaction becomes independent of water.
Which step in the Michaelis-Mentin model is the rate limiting step?
K2
Write out the Michaelis Menten Equation.
v= [vmax {S}]/[Km + {S}]
The Km value equals ___ in first order kinetics.
1/2 vmax
If you want to understand the enzyme activity, run the experiment at ___ ___ reaction conditions. If you want to understand the substrate activity, run the experiment at ___ ___ reaction conditions.
zero order, first order
What does the Km value mirror?
The substrate concentration.
The amount of substrate that yields product per molecule of enzyme available. Also called the turnover rate.
Kcat
Enzymes with a high K2/Km (or Kcat/Km) value are reaching ____ ____.
Kinetic perfection
Kcat/Km is also called the ___ ___.
Specificity constant
When comparing two enzymes, saturate with [S] and choose the enzyme with the highest what?
Specificity constant
Explanation: means that the enzyme binds to the substrate with high affinity and has a high turnover rate.
What does having an easily diffusible product (like carbon dioxide) do to the specificity constant?
Increases the value
What types of reactions form a ternary complex?
single displacement and random
How do single displacement reactions appear on a Lineweaver-Burk graph?
The lines intersect at vmax
How do double displacement reactions appear on a Lineweaver-Burk graph?
The lines are parallel
Double displacement reactions are also called ___ ___ reactions.
Ping Pong
What are the three types of reversible enzyme inhibitors?
Competitive, noncompetitive, uncompetitive
How to overcome competitive inhibition?
increase [S]
Competitive Inhibition (change or no change): Km__ and Vmax___.
No change for Km, change in Vmax
Where does the inhibitor bind in noncompetitive inhibition?
At a separate site than the substrate
Noncompetitive Inhibition (change or no change): Km__ and Vmax ___.
No change for Km, change in Vmax
What is a subcategory of noncompetitive inhibition?
Mixed inhibition
Mixed Inhibition (change or no change): Km___ and Vmax___.
Change in Km, no change in Vmax
What must happened before an uncompetitive inhibitor binds?
The enzyme and substrate are already bound
Uncompetitive Inhibition (change or no change): Km___ and Vmax___.
Km apparent change, vmax decrease
How does uncompetitive inhibition appear on a Lineweaver-Burk graph?
Parallel lines
- What does Methotrexate compete against?
- What process is shut down?
- Which enzyme is inhibited?
- folic acid
- DNA synthesis
- dihydrofolate reductase
Statins are competitive inhibitors for ___ _____ used in _____ synthesis.
HMG-CoA reductase, cholesterol synthesis
What is an example of irreversible inhibition in relation to bacteria?
Antibiotics
Explantation: drug covalently binds to Ser residue in transpeptidase which polymerizes peptidoglycan of gram (-) bacteria.
Arsenite is a noncompetitive inhibitor of what enzyme family?
Lipoamide DH
E.g. PDH, and alpha ketoglutarate DH
What enzyme stabilizes the transition state?
stickase
How do enzymes affect Keq?
Do not. Reaction reaches equilibrium faster only
What does a mixed inhibitor graph look like?
No intersection on axes. Change in both values
