Biochemistry - Ch 11 - Mechanisms Of Enzyme Action (Vocab)

Front 1

Define:

Active site

Back 1

The region of an enzyme in which catalysis takes place

Front 2

Define:

Substrate

Back 2

A reactant in an enzymatic reaction.

Front 3

Define:

Induced fit

Back 3

How enzymes undergo some conformational change upon substrate binding.

Front 4

Define:

Prochirality

Back 4

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)

Front 5

Define:

Cofactor

Back 5

A small organic molecule (coenzyme) or metal ion that is required for the catalytic activity of an enzyme.

Front 6

Define:

Coenzyme

Back 6

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.

Front 7

Define:

Cosubstrate

Back 7

A coenzyme that is only transiently associated with an enzyme so that it functions as a substrate.

Front 8

Define:

Prosthetic group

Back 8

A cofactor that is permanently (often covalently) associated with an enzyme.

Front 9

Define:

Holoenzyme

Back 9

A catalytically active enzyme-cofactor complex.

Front 10

Define:

Apoenzyme

Back 10

An enzyme that is inactive due to the absence of a cofactor.

Front 11

Define:

Transition state

Back 11

A molecular assembly at the point of *maximal free energy* in the reaction coordinate diagram of a chemical reaction.

Front 12

Define:

ΔG‡

What is this called?

Back 12

Free energy of activation:

The free energy of the transition state minus the free energies of the reactants in a chemical reaction.

Front 13

Define:

Rate determining step

Back 13

The step with the highest transition state free energy in a multi-step reaction.

i.e. The SLOWEST step

Front 14

Define:

General acid catalysis

Back 14

A catalytic mechanism in which partial proton transfer from an acid lowers the free energy of a reaction's transition state.

Front 15

Define:

General base catalysis

Back 15

A catalytic mechanism in which partial proton abstraction by a base lowers the free energy of a reaction's transition state.

Front 16

Define:

Covalent catalysis

Back 16

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.

Front 17

Define:

Metalloenzyme

Back 17

An enzyme that contains a tightly bound metal ion cofactor, typically a transition metal ion such as:

Fe²+ , Zn²+ , Mn²+

Front 18

Define:

Electrostatic catalysis

Back 18

A catalytic mechanism in which the distribution of charges about the catalytic site lowers the free energy of a reaction's transition state.

Front 19

Define:

Transition state analog

Back 19

A stable substance that geometrically and electronically resembles the transition state of a reaction.

Front 20

Define:

Oxonium ion

Back 20

A resonance-stabilized carbocation such as occurs during the lysozyme-catalyzed hydrolysis of a glycoside.

Front 21

Define:

Serine protease

Back 21

A peptide-hydrolyzing enzyme characterized by a reactive SER residue in its active site.

Front 22

Define:

Affinity labeling

Back 22

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.

Front 23

Define:

Catalytic triad

Back 23

The hydrogen-bonded SER, HIS, and ASP residues that participate in catalysis in serine proteases.

Front 24

Define:

Tetrahedral intermediate

Back 24

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.

Front 25

Define:

Acyl-enzyme intermediate

Back 25

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.

Front 26

Define:

Oxyanion hole

Back 26

A structure in enzyme active site that preferentially binds and thereby stabilizes the oxyanionic tetrahedral transition state of the reaction.

Front 27

Define:

Proenzyme

Back 27

An inactive precursor of an enzyme.