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32 Cards in this Set

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  • Back
What is the definition of a Catalyst?
A substance that accelerates the rate or ease of a chemical reaction without itself being changed or consumed in the end
What is the definition of Gibb's Free Energy?
The energy portion of a thermodynamic system available to do work
What does an enzyme do to a reaction?
The enzyme's major role isn't to affect the equilibrium of a reaction, but rather to affect the rate at which the equilibrium is reached, by lowering the energy of activation.
What are the mechanistic considerations for Enzymes? (4)
1) Binds to reaction substrates and products to varying degrees, but binds to TS quite well

2) Increases the effective concentration of reactants by bringing them in proximity to one another

3) Holds reactants in an optimal orientation for catalysis

4) Covalent chemistry effects occur when a covalent bond is made by the enzyme (or bound cofactor) to its substrate being transformed

What is the characteristic of a competitive inhibitor of the enzyme?
If the enzyme binds preferentially to the Transition State then it can be expected that a TS analogue can be a potent competitive inhibitor of the enzyme
"Tethered reactions have a faster rate than non-tethered reactions" True or False?
What are the components of the Chymotrypsin active site? (4)
1) Asp102

2) His57

3) Ser195

4) Oxyanion Hole

What is Vmax?
The theoretical maximal rate at which the total enzyme concentration is making product
What is Km?
The substrate concentration at which the rate of the reaction is half maximal
"Km is considered a constant for an enzyme's affinity for its substrate" True or False?
What does the rate constant for the enzyme reaction become when k2>>k-1?
kcat/km = k1
What is the definition of an Enzyme Inhibitor?
A substance that reduces an enzyme's activity by combining with it in such a way that influences the binding of substrate and/or its catalysis
What are the different ways an Inhibitor can bind?
Inhibitors can bind irreversibly or reversibly to the active site or to the allosteric site.
What is Irreversible Inhibition?
The instance when an inhibitor binds covalently or very tightly to an enzyme in a way that prevents it from functioning
What is "Inhibition Efficiency"?
The apparent second order rate constant for enzyme inactivation
What are examples of Irreversible Inhibitors? (7)
1) Sarin

2) Cyclosarin

3) Tabun

4) Soman

5) Dyflos

6) VX

7) Acethycholine

What does Oxidative Desulfrization do and why does it result in toxcities found in animals?
Converts Malathion into its toxic metabolite Malaoxon.

This can result in toxicities found in animals

What are "Active Site Directed Irreversible Inhibitors"?
Chemical entities inherently reactive & indiscriminate, thus offering little therapeutic value
What is an example of Active Site Directed Irreversible Inhibitors?
What are "Mechanism based irreversible inhibitors"?
These "suicide substrates" are highly & selectively reactive toward an enzyme's catalytic cycle.

They are differentiated from active site directed inhibitors in that they have an extra level of built in selectivity.

What is an example of Mechanism based irreversible inhibitors?
Penicillin & Aspirin Alkylate
What are the suicide substrate requirements? (5)
1) Inactivation should be time dependent (reaction is irreversible)

2) Kinetics should be first order with respect to X

3) The enzyme should show saturation kinetics

4) The substrate should be able to block the enzyme 5) Stoichiometry of the reaction should be 1:1

What is Reversible Inhibition?
The instance when an inhibitor exists in equilibrium with the enzyme it affects.
What is a Competitive Inhibitor?
When an inhibitor competes with substrate for free enzyme to form enzyme:inhibitor complex
What is a Uncompetitive Inhibitor?
When an inhibitor binds only to the enzyme:substrate complex to form an enzyme:substrate:inhibitor complex
What is a Mixed Inhibitor?
When an inhibitor binds to the free enzyme OR the enzyme:substrate complex
What is effect of competitive inhibition on Vmax apparent and Km apparent?
Vmax apparent = Vmax. Km apparent = αKm.
What is effect of uncompetitive inhibition on Vmax apparent and Km apparent?
Vmax apparent = Vmax/α'. Km apparent =Km/α'.
What is effect of mixed inhibition on Vmax apparent and Km apparent?
Vmax apparent = Vmax/α'. Km apparent =αKm/α'.
What is effect of non-competitive inhibition on Vmax apparent and Km apparent?
Vmax apparent = Vmax/α'. Km apparent =αKm/α'; α=α'
What are the methods that Ki can be determined? (2)
1) Lineweaver-Burke Plot 2) Eadie-Hofstee Plot
What is IC50?
The concentration of inhibitor required to inhibit an enzyme by 50%