Enzymes: Discovery, Structure, Mechanism, and Classification

A set of vocabulary flashcards covering basic enzyme definitions, key historical discoveries, mechanisms, specificity, and the six major enzyme classes.

Enzyme

A biological catalyst that increases the rate of a chemical reaction without being consumed overall.

Ribozyme

A catalytic RNA molecule that performs enzyme-like catalysis.

Diastase

An enzyme preparation extracted from malt in 1833 by Payen & Persoz, recognized as one of the first enzyme preparations.

Wilhelm Kühne

The scientist who introduced the term "enzyme" in 1878 (from Greek, meaning "in leaven") to describe the active agent associated with fermentation.

Lock-and-Key Model

A model proposed by Emil Fischer in 1894 suggesting that an enzyme's active site and its substrate have rigid, complementary shapes.

Induced-Fit Model

A model proposed by Daniel Koshland in 1958 suggesting that substrate binding induces a conformational shape change in the enzyme's active site to position catalytic groups correctly.

James Sumner

The scientist who isolated and crystallized urease from jack beans in 1926, proving that enzymes can be proteins.

Activation Energy ($E_a$)

The energy barrier required for a chemical reaction to occur, which enzymes lower without altering overall free-energy difference ($\Delta G$) or reaction equilibrium.

Active Site

A three-dimensional region of an enzyme where substrate binding and catalysis occur.

Absolute Specificity

Enzyme specificity where an enzyme acts on only one substrate or a very narrow set of substrates.

Group Specificity

Enzyme specificity where an enzyme recognizes a particular functional group or bond.

Bond Specificity

Enzyme specificity where an enzyme targets a particular type of chemical bond.

Stereospecificity

Enzyme specificity where an enzyme distinguishes between different 3-D forms (stereoisomers) of a molecule.

Cofactor

A non-protein helper required by some enzymes for catalytic activity, often a metal ion such as $Mg^{2+}$, $Zn^{2+}$, $Fe^{2+}/Fe^{3+}$, or $Cu^{2+}$.

Coenzyme

An organic cofactor often derived from vitamins, such as $NAD^+$ and $FAD$.

Holoenzyme

The complete, catalytically active enzyme containing both its protein component and required cofactor(s).

Apoenzyme

The protein portion of an enzyme alone, which remains inactive without its required cofactor.

Oxidoreductases

The enzyme class (EC Class 1) that catalyzes oxidation-reduction (redox) reactions involving electron transfer or hydrogen equivalents.

Transferases

The enzyme class (EC Class 2) that catalyzes the transfer of functional groups (such as methyl, amino, or phosphoryl groups) from one donor molecule to an acceptor molecule.

Hydrolases

The enzyme class (EC Class 3) that catalyzes chemical bond cleavage using water ($H_2O$).

Lyases

The enzyme class (EC Class 4) that adds or removes groups to form or eliminate double bonds without using hydrolysis or oxidation-reduction.

Isomerases

The enzyme class (EC Class 5) that catalyzes intramolecular rearrangements, converting a molecule into its isomer without changing its net atomic formula.

Ligases

The enzyme class (EC Class 6) that catalyzes the joining of two molecules coupled with energy input from ATP hydrolysis.