Enzyme Biochemistry and Kinetics

A comprehensive set of vocabulary flashcards based on lecture notes covering enzyme classifications, components, kinetic models, inhibition types, and regulatory mechanisms.

Enzymes

Proteins that act as catalysts within living cells, increasing reaction rates by a factor of $10^6$ to $10^{20}$ over uncatalyzed reactions.

Amylase

An enzyme found in saliva that breaks down starch into maltose.

Pepsin

A digestive enzyme found in gastric juices with an optimum $pH$ of $2.0$.

Simple enzyme

An enzyme composed only of protein (amino acid chains).

Conjugated enzyme

An enzyme that has a non-protein part in addition to a protein part.

Apoenzyme

The protein part of a conjugated enzyme.

Holoenzyme

A biochemically active conjugated enzyme formed by the combination of an apoenzyme and a cofactor.

Active site

A relatively small pocket or cleft in an enzyme's structure where the reaction occurs or where the substrate binds.

Proenzyme (Zymogen)

An inactive form of an enzyme that becomes active after undergoing a chemical change.

Cofactor

A nonprotein portion necessary for catalytic function; can be metallic ions like $Zn^{2+}$, $Mg^{2+}$, $Mn^{2+}$, and $Fe^{2+}$ or nonmetallic ions like $Cl^-$.

Coenzyme

A nonprotein organic molecule, frequently derived from dietary B vitamins, that acts as a cofactor.

Oxidoreductases

A class of enzymes that catalyze oxidation-reduction reactions, such as lactate dehydrogenase.

Transferases

Enzymes that catalyze the transfer of a functional group from one molecule to another, including transaminases and kinases.

Hydrolases

Enzymes that catalyze hydrolysis reactions involving the addition of a water molecule to cause bond breakage.

Lyases

Enzymes that catalyze the addition of a group to a double bond or removal of a group to form a double bond without hydrolysis or oxidation.

Isomerases

Enzymes that catalyze isomerization reactions, which involve the rearrangement of atoms within a molecule.

Ligases

Enzymes that catalyze the joining of two molecules, a process involving $ATP$ hydrolysis.

Substrate saturation

The concentration at which the reaction reaches its maximum rate and all active sites are occupied.

Turnover Number

The number of substrate molecules converted to product per second per enzyme molecule under optimum conditions.

Optimum temperature

The temperature at which the rate of an enzyme-catalyzed reaction is maximum; for human enzymes, this is $37^\text{o}C$.

Lock-and-Key Model

A model proposed by Emil Fischer describing the enzyme as a rigid body where the active site specifically fits the substrate like a key.

Induced Fit Model

A model proposed by Daniel Koshland stating the enzyme modifies the shape of its active site to accommodate the substrate.

Competitive inhibitor

A substance resembling the substrate in shape and charge that binds reversibly to the active site, preventing substrate binding.

Noncompetitive inhibitor

A substance that binds to an allosteric site (a site other than the active site), changing the conformation of the active site so the substrate no longer fits.

Uncompetitive inhibition

An inhibition process where the inhibitor binds specifically to the enzyme-substrate ($ES$) complex.

Irreversible inhibitor

A substance that inactivates enzymes by forming a strong covalent bond with the active site, permanently deactivating the enzyme.

Absolute specificity

The most restrictive specificity where an enzyme catalyzes only one reaction, such as Catalase acting only on $H_2O_2$.

Stereochemical specificity

The property where an enzyme acts only on a particular stereoisomer, such as $L$-amino-acid oxidase only acting on $L$-forms.

Feedback control

An enzyme regulation process where the formation of a product inhibits an earlier reaction in the sequence.

Isoenzymes

Enzymes that perform the same function but have different combinations of subunits and different quaternary structures.