Enzyme Kinetics and Inhibition

Question 1

How does enzyme regulation often take place?

Answer 1

Through inhibition (stops enzyme from working properly)

Question 2

What is an inhibitor?

Answer 2

It is a substance that interacts with an enzyme in a way that prevents it from catalyzing the reaction that it normally would.

Question 3

Is inhibition reversible?

Answer 3

Yes, well almost always.

Question 4

How does an inhibitor bind to enzyme?

Answer 4

Through non-covalent interactions.

Question 5

What are irreversible inhibitors which form covalent bonds with enzymes called? (Not common on MCAT)

Answer 5

Suicide Inhibitors

Question 6

On the level of individual molecules, can inhibitors completely block an enzyme from functioning?

Answer 6

Yes

Question 7

In real-life, what happens when we apply inhibitors?

Answer 7

We are only going to interfere with some of the reaction. Applying the inhibitor will just slow down the reaction not completely stop it.

Question 8

What does the Michaelis-Menten Model tell us?

Answer 8

It underpins everything that we say about enzyme kinetics and inhibition.

Question 9

What does it mean for enzymes to be saturated?

Answer 9

It means that all molecules of an enzyme are occupied. This is the point that the enzyme-catalyzed reaction is at its maximum rate (Vmax).

Question 10

What does Vmax stand for?

Answer 10

The maximum rate of reaction

It is one of the two key variables in Michaelis-Menten Kinetics

Question 11

What does Km stand for?

Answer 11

It is the concentration of substrate that corresponds to half of Vmax. It measures how readily an enzyme interacts with its substrate. Is is the [S] at 1/2 Vmax

Question 12

Equation for finding velocity in Michaelis-Menten Model

Answer 12

V= (Vmax x [S]) / (Km + [S])

Question 13

What does a high Km mean?

Answer 13

Enzyme has low affinity for its substrate

Question 14

What does a low Km mean?

Answer 14

Enzyme has high affinity for its substrate

Question 15

Describe a Michaelis-Menten Plot.

Answer 15

It has reaction rate or V on Y-axis and it has substrate concentration on X-axis.
It has a fixed concentration of enzyme
Graph has hyperbolic shape
Never reaches Vmax (forms asymptote)

Question 16

What do Michaelis-Menten Curves show?

Answer 16

They show how changes in substrate concentrations affect reaction speed, given a fixed quantity of enzyme.

Question 17

Why does reducing enzyme concentration also decrease the Vmax of the enzyme-catalyzed reaction?

Answer 17

Because there are fewer enzyme molecules available to catalyze the reaction.

Question 18

Describe the Lineweaver-Burk Plot

Answer 18

Double-reciprical transformations of the Michaelis-Menten Plots. It assigns very specific graphical coordinates to the important parameters of Km and Vmax
X-intercept = -1/Km
Y-intercept = 1/Vmax

Question 19

What does increasing Vmax do to the Lineweaver-Burk Plot?

Answer 19

Makes Y-intercept smaller

Question 20

What does decreasing Vmax do to the Lineweaver-Burk Plot?

Answer 20

Makes Y-intercept larger

Question 21

What does increasing Km do to the Lineweaver-Burk Plot?

Answer 21

Makes X-intercept have a greater value (brings x-intercept closer to origin)

Question 22

What does decreasing Km do to the Lineweaver-Burk Plot?

Answer 22

Makes X-intercept have a lesser value (moves x-intercept further away from origin)

Question 23

What are the four key types of reversible inhibition?

Answer 23

Competitive
Noncompetitive
Uncompetitive
Mixed

Question 24

What are competitive inhibitors? What do they do to the MMP and LBP

Answer 24

They compete with the substrate for the active site.
Vmax = same, Km = up
MMP- hyperbolic line starts below but eventually reaches
uninhibited’s curve’s Vmax.
LBP- y-intercept stays the same
x-intercept moves closer to the origin
So slope gets steeper.

Question 25

What are noncompetitive inhibitors? What do they do to the MMP and LBP

Answer 25

They interact with enzyme allosterically.
Vmax = decreases, Km = same
MMP- hyperbolic line stays below uninhibited curve the
entire time
LBP- y-intercept increases
x-intercept stays the same
So slope gets steeper.

Question 26

What are uncompetitive inhibitors? What do they do to the MMP and LBP

Answer 26

They interact with enzyme-substrate complex at an allosteric site and essentially prevent the enzyme from letting go of the substate after it is bound.
Vmax = decreases, Km = down
MMP- hyperbolic line starts higher but then ends below
uninhibited’s curve
LBP- y-intercept increases
x-intercept moves further away from origin

Question 27

What are mixed inhibitors? What do they do to the MMP and LBP

Answer 27

They either bind to free enzyme at an allosteric site or bind to the enzyme-substrate complex
Vmax = decreases, Km = up if it binds to free enzyme
Km = down if it binds to E-S complex
MMP- hyperbolic line always ends below the uninhibited
curve. But the curve of the graph depends on
binding preference
LBP- y-intercept increases
x-intercept moves closer to the origin if it binds to
free enzyme and further away if it binds to E-S
complex.

Question 28

What type of inhibitors are substrate analogs?

Answer 28

Competitive inhibitors because they share structural features with the enzymes endogenous substrate, which allows them to bind to the active site of the enzyme.

Question 29

What does the Michaelis-Menten Plot show?

Answer 29

It shows how changes in the SUBSTRATE concentration affect the speed of the reaction. Enzyme concentration is held constant.