Enzyme kinematics Flashcards
(33 cards)
A catalyst (enzyme) does not change the reaction rate or [equilibrium] of a reaction. Only the ____ changes
Activation energy
Lowered like a catalyst
The maximum velocity is ______
The top velocity that all variations of the experiment reached (meaning, all the different [S]
Km occurs at _____ and represents ____
1/2 Vmax
The binding affinity for that reaction (inversely related)
On the affinity graph (the normal graph that shows Vmax) the __ axis represents initial velocity and the __ axis represents [S]
Y
X
Why is ES a vital stage in the reaction scheme?
At the formation of ES, the reaction can either proceed backwards to the E+S stage or forwards to the E+P stage. This makes the ES stage a vital part of the entire reaction
The Briggs Haldane Assumption said that ____ reaches a steady state of rate formation where rate of formation = rate of breakdown, so that it is fixed for most of the reaction
[ES]
It is the assumption that ____ is the rate limiting state of the reaction
ES –> E+P
The Michaelis-Menten Equation is:
Vo= Vmax[S]/Km+[S]
Km is the ___ at ___ and represents the rate of speed of the reaction. It can be calculated by:
[S] at 1/2 Vmax
Km= (k2+k-1)/K1
The Lineweaver-Burk equation is:
1/Vo= (Km/Vmax) * (1/[S]) + (1/Vmax)
Where are 1/Vmax and -1/Km on the Lineweaver-Burk plot?
1/Vmax is found on the y-intercept
-1/Km is found on the x intercept
Km is ____ proportional to enzyme affinity, meaning:
Inversely
The higher the Km, the lower the affinity for enzyme to substrate and therefore the higher [S] needed to reach Vmax, and vice versa
Kcat represents the _____ and is calculated by:
Turnover rate (the maximum amount of molecules that are turned into products when the enzyme and substrate are bound)
Kcat= Vmax/[E]
Kcat/Km is the _____ (2nd order rxn) which is the overall measure of catalytic affinity, meaning:
Specificity constant
The rate of turnover and affinity for the substrate. It can be used to compare different substrates with the same or different enzymes
10^___ is the “perfect” diffusion rate- meaning, the fastest the enzyme can go
10^8 or 10^9
Why is it important that many enzymes are “imperfect”?
Enzymes are responsible for a lot of cleavage, so it would be bad if they cleaved everything they came across
The sequential method, one of the two possible methods when there are two or more reactants involved, occurs when:
Both of the substrates must bind to the enzyme before any product is made. Makes a complex something like: ES1S2 –> E+P1+P2
It forms a ternary complex where either substrate can come in first, but ultimately results in the formation of 2 products
The ping-pong method, one of the two possible methods when there are two or more reactants involved, occurs when:
The enzyme reacts with one substrate, turns that into a product, and then reacts with another substrate. No ternary complex is formed and the substrates come in like ping-pong balls
The Km of a reaction with a competitive inhibitor is ____ bc the inhibitor lowers the binding affinity as it outcompetes the substrate
Higher
(inversely proportional)
A competitive inhibitor keeps the same ____ as the reaction without the inhibitor because
Vmax
At some point, you will be able to outcompete the inhibitor since it binds to the active site
A _____ inhibitor binds at E+S and fits into the same pocket as the substrate does
Competitive
An _____ inhibitor binds the ES complex and not the enzyme by itself
Uncompetitive
A _____ inhibitor can bind to both the E+S and ES complex
Noncompetitive
A competitive inhibitor can be identified on a Lineweaver-Burk plot by the ____
1/Vmax, since Vmax stays the same with or without inhibitors, all the lines will have the same y intercept regardless of slope
