Enzyme Kinetics Flashcards
What is K1 in terms of enzyme kinetics?
K1 is the rate of the forward reaction to form the ES complex
What is K -1 in terms of enzyme Kinetics?
K-1 is the rate of the backward reaction from the ES complex to E + S
What is the general equation used to show how enzymes catalyse reactions?
E + S -> ES -> E + P
What is the Michaelis constant (Km) ?
It describes the rate at which the enzyme substrate (ES) complex is formed
What is the Michaelis Constant equation (Km) ?
Km = (K-1 + K2) / K1
What is K2 in terms of enzyme Kinetics?
K2 is the rate of the second forward reaction, from Es to form the E + P
If an enzyme follows the Michaelis-Menten Kinetics, by what two values can it be described?
V max - The maximal rate of reaction at unlimited substrate level
Km
What is Vmax in terms of Michaelis Menten Kinetics?
The Maximal rate of reaction at unlimited substrate level
How do you determine the velocity at which a reaction occurs?
The Progress of a reaction is record for a substrate
Product Vs Time graph
After some time equilibrium is reach - No more net change of substrate and product
Tangents/Gradients of the curve at specific points is the velocity
Plot a graph of Velocity vs Substrate
At infinite substrate concentration the reaction rate approaches Vmax
What is the Michaelis Constant (KM) equivalent to?
Km = the substrate concentration were it is half V max
What is the concentration of Km?
(M) molar
What does a low Km mean?
A low Km means that an enzyme only needs a little substrate to work at half maximal velocity
What does a high Km mean?
A high Km means that an enzyme needs a lot of substrate to work at half maximal velocity
How can the Michaelis Menten equation be graphically defined?
A Michaelis Menten equation can be rearranged to form a Lineweaver Burk Pot (straight line graph)
This is a lot easier to read the V max
How do you find the V max on a Lineweaker - Burk Plot?
Where the straight line crosses the Y axis is 1/Vmax
How do you find the Km on a Lineweaker - Burk Plot?
Where the straight line corsses the X axis is -1/Km
Is the Km the same for Isoforms?
No
What is a reversible inhibitor?
A substance that binds to an enzyme to inhibit it, but which can be released
What are the two types of Reversible inhibitors?
- Competitive: Binds to the active catalytic site and blocks access to it by substrate
- Non-competitive: Binds to a site other than the active site and changes its conformation
What is an Irreversible Inhibitor?
A substance that causes inhibition that cannot be reversed
What happens to the Km if a competitive inhibitor is present
The Km will increase - It requires more substrate to reach half of Vmax
What happens to Vmax if a competitive inhibitor is present?
Vmax will remain the same
What happens to the Vmax if a non-competitive inhibitor is present?
The V max will decrease
The 1/Vmax will look like it has increased, only as it is a reciprocal
What are the mechanisms of enzyme control?
Allosteric Control Regulation of trascription Reversible Covalent Bond Modication Irreversible Covalent Bond modification Degradation
What is a common inhibiting rate limiting step?
Allosteric Control
Enzyme requires a high Km, this means there will be a rate limiting step - as concentration levels need to build
Do Allosteric Enzymes follow Michaelis Menten Kinetics?
No.
What is an allosteric enzyme?
Allosteric enzymes are enzymes that change their conformational ensemble upon binding of an effector,
What type of Reaction(V) vs Substrate graph does a Allosteric enzyme form?
A sigmoidal curve
ALLOSTERIC ENZYMES DO NO CONFORM TO KM
What does a sigmoidal curve on a Reaction(V) vs Substrate graph indicate?
Indicates co-operative behaviour
What are Allosteric ezymes governed by?
Allosteric activators
Allosteric Inhibitors
What does a Allosteric inhibitor do to the sigmoidal curve on a Reaction(V) vs Substrate graph?
It causes a right shift - Causes the Vmax to lower and is less step
What does a Allosteric Activator do to the sigmoidal curve on a Reaction(V) vs Substrate graph?
It causes a left shift - Causes Vmax to increase and has a steeper gradient
What does co-operativity in terms of allosterism mean?
The influence of a binding ligand to a receptor that has an effect on the binding of another ligand to bind to a receptor
What are the two ways an enzyme can bind a substrate?
R (relaxed) - Binds substrate tightly [This is the active form]
T (Tight) - Binds substrate less tightly. [This is the inactive forms}
What affect does a substrate have when it binds to allosteric enzyme ?
Changes the enzyme from the Tight form to the relaxed form
This causes other subunits to change
