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27 Cards in this Set
- Front
- Back
Define:
Active site |
The region of an enzyme in which catalysis takes place
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Define:
Substrate |
A reactant in an enzymatic reaction.
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Define:
Induced fit |
How enzymes undergo some conformational change upon substrate binding.
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Define:
Prochirality |
A property of some nonchiral molecules such that they contain a group whose substitution by another group yields a chiral molecule.
(i.e. they become chiral by having a group replaced) |
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Define:
Cofactor |
A small organic molecule (coenzyme) or metal ion that is required for the catalytic activity of an enzyme.
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Define:
Coenzyme |
A small organic molecule that is required for the catalytic activity of an enzyme.
A coenzyme may be either a cosubstrate or a prosthetic group. |
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Define:
Cosubstrate |
A coenzyme that is only transiently associated with an enzyme so that it functions as a substrate.
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Define:
Prosthetic group |
A cofactor that is permanently (often covalently) associated with an enzyme.
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Define:
Holoenzyme |
A catalytically active enzyme-cofactor complex.
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Define:
Apoenzyme |
An enzyme that is inactive due to the absence of a cofactor.
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Define:
Transition state |
A molecular assembly at the point of *maximal free energy* in the reaction coordinate diagram of a chemical reaction.
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Define:
ΔG‡ What is this called? |
Free energy of activation:
The free energy of the transition state minus the free energies of the reactants in a chemical reaction. |
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Define:
Rate determining step |
The step with the highest transition state free energy in a multi-step reaction.
i.e. The SLOWEST step |
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Define:
General acid catalysis |
A catalytic mechanism in which partial proton transfer from an acid lowers the free energy of a reaction's transition state.
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Define:
General base catalysis |
A catalytic mechanism in which partial proton abstraction by a base lowers the free energy of a reaction's transition state.
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Define:
Covalent catalysis |
A catalytic mechanism in which the transient formation of a covalent bond between the catalyst and a reactant lowers the free energy of a reaction's transition state.
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Define:
Metalloenzyme |
An enzyme that contains a tightly bound metal ion cofactor, typically a transition metal ion such as:
Fe²+ , Zn²+ , Mn²+ |
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Electrostatic catalysis |
A catalytic mechanism in which the distribution of charges about the catalytic site lowers the free energy of a reaction's transition state.
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Define:
Transition state analog |
A stable substance that geometrically and electronically resembles the transition state of a reaction.
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Define:
Oxonium ion |
A resonance-stabilized carbocation such as occurs during the lysozyme-catalyzed hydrolysis of a glycoside.
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Define:
Serine protease |
A peptide-hydrolyzing enzyme characterized by a reactive SER residue in its active site.
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Define:
Affinity labeling |
A technique in which a labeled substrate analog reacts irreversibly with, and can thereby be used to identify a group in an enzyme's active site.
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Define:
Catalytic triad |
The hydrogen-bonded SER, HIS, and ASP residues that participate in catalysis in serine proteases.
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Define:
Tetrahedral intermediate |
An intermediate of peptide bond hydrolysis in which the carbonyl carbon of the scissile bond (bond to be cleaved) has undergone nucleophilic attack so that it has four substituents.
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Define:
Acyl-enzyme intermediate |
An intermediate of peptide bond hydrolysis in which the carbonyl carbon of the scissile bond (bond to be cleaved) is covalently bound to the enzyme nucleophile that attacked it.
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Define:
Oxyanion hole |
A structure in enzyme active site that preferentially binds and thereby stabilizes the oxyanionic tetrahedral transition state of the reaction.
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Define:
Proenzyme |
An inactive precursor of an enzyme.
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