Enzymes : mechanisms and kinetics Flashcards
How does enzyme work
work by reducing the energy barrier or free energy of activation (∆G) by bringing the substrates to closer to the enzyme at the active site.
what are the factors influencing the rx rates?
- pH
- Enzyme concentration
- Substrate concentration
- Stability of the enzyme substrate complex
- Concentration of the products
- Temperature
- ionic strength
what is the effect of ionic strength on the rxn rate
low salt concentration can help enzyme but high concentrations will force the enzyme to go in solution and decrease the rxn rate
what is the end-point method?
End point assay in which substrate is incubated with the enzyme for a fixed period of time. The reaction is stopped and the amount of product formed or substrate used is estimated.
What are the disadvantages of end point method
- over time the enzyme lose activity
- there is a substrate depletion
- products may inhibit enzymes
What are the advantages of initial rate method
it is a true measure of the rate of the enzyme activity because no product has formed to cause inhibition and the substrate concentration is at the maximum.
what are the three phases of enzyme reactions?
A transient phase or pre-steady phase
B steady state phase
C exhaustation phase or post steady phase
in the post steady phase, the rxn rate is ____
decreasing
in the pre-steady phase, the rxn rate is ___
increasing
In the steady phase, the rxn rate is ____
constant
in the pre-steady phase
k1 > k2 + k3
in the steady phase
k1 = k2 + k3
in the post-steady phase
k2 + k3 > k1
What is the michealis menten equation of V0
V0 = Vmax * [S] / Km + [S]
What is the lineweaver - burke plot
1/V0 = Km / Vmax * 1/[S] + 1/Vmax
What is the Km ?
the substrate concentration at which the V0 is equal to half of the Vmax. Km is the ratio of k2 + k3 / k1. So when km is high the affinity for the enzyme is low because there is more breakdown than formation. When the Km is low, it means that the affinity is high.
Lower is the Km, better is _____
the affinity of the enzyme to the substrate
What is the Vmax ?
Vmax is the maximum rate of a reaction. it is rached when the enzyme is saturated.
What does the Vmax / km ratio measures
the catalytic efficiency
What type of enzyme inhibition is this : Strong covalent bond at the active site of the enzyme.
irreversible
What type of enzyme inhibition is this : : non-covalent interaction
reversible
What are the three type of reversible inhibition?
- competitive
- non competitive
- uncompetitive
Describe competitive inhibition and give an example
the inhibtor will bind at the active site and prevent the binding of the substrate.
ex : inhibition of succinate dehydrogenase by malonate
Describe non-competitive inhibition and give an example
can act as both competitive inhibitor and uncompetititive becuse the inhibitor binds to a site other than the active site.
ex : inhibition of the Rx rate by the pH
Describe uncompetitive inhibition and give an example
The inhibitor binds to a site that is only available after the substrate has bound to the active site.
ex : inhibition of invertse by high sucrose concentration
