Lecture 12: Kinetics Flashcards
Enzyme Kinetics I
What role do enzymes have in:
Keq
ΔG
Ea
Keq - No Effect
ΔG - Decrease
Ea - Decrease
Are enzymes produced or consumed by reactions which they catalyze?
No, Catalysts are neither produced or consumed by reactions.
Zero Order:
Rate of Reaction Independent of:
Depending on:
Commonly seen on M-M Plot?
Independent of [S]
Depending on other factor–pH, Temp
As the slop approaches Vmax
First Order:
Proportional to:
Commonly Seen on M-M Graph:
Rate is proportional to [S]
The early climbing stage of M-M plot
Second Order:
Proportional to:
How do we usually handle this biologically, and why?
Proportional to [S1] and [S2]
If [S2] is >>> [S1] , [S1] will be rate limiting step, and we ignore [S2] ; commonly this is water in a biological approach
Treat as First Order
How do you calculate Km from a M-M plot or series of numbers?
How do you calculate Vmax?
Km = 1/2 Vmax
Vmax = Asymptote which graph approaches (or number if given table of values)
What is the rate limiting step in First Order kinetics?
Zero Order?
Collision of Substrate with Enzyme (there are open enzymes available)
Product Release from Enzyme (enzyme fully saturated)
What is the x-intercept on a Lineweaver Burk Plot?
What is the y-intercept on a Lineweaver Burk Plot?
What is the X-axis?
Slope?
X-intercept = -1/Km
Y-intercept = 1/Vmax
X-axis = 1/[S]
Slope = Km/Vmax
Which will have greater binding, a small Km or large Km?
Small Km = Tight Binding
Large Km = Weak Binding
What approximates the physionlogical concentation of true substrate in many cases?
Km
How would you determine which substrate has a higher affinity for a substrate given two enymes plotted on a M-M plot?
The smaller Km will have a higher affinity
(Km=1/2 Vmax)
How would you determine which substrate binds best when given a table including an enzyme, multiple substrates, and Km values?
The lowest Km has the highest affinity
What is the number of substrate molecules converted to product per enzyme molecue per unit time?
kcat
Which is a better enzyme, a large kcat or a small kcat?
Large Kcat = better enzyme
In living cells, are enzymes usually saturated?
No
How would you mathematically determine the “best” enzyme in a living cell given the following:
Why is the rate usually <<< k2K
Largest Ratio of k2 / Km
[S] usually < Km
Enzymes reaching what specificity constant value are considered “perfect”?
108
What is the specificity constant of an enzyme?
kcat / Km
How do enzymes vary with temperature?
At what T does full denaturation usually occur?
What is the optimum tenperature for most enzymes?
Activity usually doubles w/ 10oC increase
Denatured at 70oC
~ 30oC
In Single-Displacement reactions, what must occur before catalysis can proceed?
In Double-Displacement (ping-pong), what must occur for catalysis to proceed?
Both Substrates must combine with the enzyme
One or more products are released from the enzyme before all substrates are added
On a Lineweaver-Burk Plot, what will the following plots be?
Single Displacement
Double Displacement (ping pong)
Several non-parallel lines, intersecting at a Ternary Complex
Parallel lines
What are the classes of Reversible Inhibitors?
What are Irreversible Inhibitors? Examples?
Reversible: Competitive and Noncompetitive Inhibitors
Irreversible: Covalent, permanent modification. Examples include antibiotics, which block bacteria cell walls.
What effect on Vmax and Km do Competitive Inhibitors have?
Why? Can this be overcome?
What will be the appearance of Competitive Inhibition on a Lineweaver-Burk Graph?
What will be the appearance of Competitive Inhibition on a MM-plot?
Km - Increase
Vmax - No Change
Inhibitor competes with substrate for binding site, at infinite [S], Inhibitor has no effect.
Lineweaver Burk: Non parallel lines intersecting at the y-intercept, or 1/Vmax
M-M Plot: Similar shape, with increased Km
