ENZYMES

Flashcards on Enzymes

Enzymes

Biological catalysts that speed up the rate of chemical reactions in the body.

Structural Features of Enzymes

Globular proteins (except ribozymes which are RNA) with high catalytic power and specificity.

Cofactors

Non-protein components required by many enzymes for activity, can be coenzymes or metal cofactors.

Nomenclature of Enzymes

Enzymes are commonly named based on the reaction they catalyze and/or the compound they act on.

Oxidoreductases

Catalyze oxidation and reduction reactions.

Transferases

Catalyze the transfer of a group of atoms from one molecule to another.

Hydrolases

Catalyze hydrolysis reactions.

Lyases

Catalyze the addition of two groups to a double bond or the removal of two groups to create a double bond.

Isomerases

Catalyze isomerization reactions.

Ligases

Catalyze the joining of two molecules (also known as synthetases).

Enzyme Mechanism

Enzymes lower the activation energy of a reaction.

Enzyme Substrate Complex

Enzyme binds to the substrate to form the ES complex.

Lock-and-key Model

Enzyme molecule has a particular shape to maintain the active site in the required conformation.

Induced fit model

Binding of the substrate induces a conformational change in the enzyme for a complementary fit.

Active Site

Three-dimensional cleft or crevice formed by groups from different parts of the amino acid sequence.

Most common amino acids in active sites

His>Cys>Asp>Arg>Glu

Enzyme Inhibitor

Substance that slows or stops the normal catalytic function of an enzyme by binding to it.

Irreversible inhibitors

Inactivate enzymes by forming a strong covalent bond to an amino acid side-chain group at the enzyme’s active site.

Competitive inhibitors

Molecules that compete with the substrate for occupancy of the enzyme’s active site.

Non-competitive inhibitors

Molecules that decrease enzymatic activity by binding to a site other than the active site.

Uncompetitive inhibitors

Molecules that decreases enzymatic activity by binding to the enzyme-substrate complex.

Allosteric Enzymes

Enzymes with quaternary structures with 2 kinds of binding site, one for the substrate and the other for the regulator.

Feedback Control

Activation or inhibition of the first reaction in a reaction sequence is controlled by a product of the reaction sequence.

Proenzymes (zymogen)

Inactive form of enzymes that must be activated to perform catalytic functions.

Covalent Modification

Enzyme activity is altered by covalently modifying the structure of the enzyme.

Isoenzymes

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

Angiotensin-converting Enzyme (ACE) inhibitor

Inhibit the enzymes used to activate angiotensinogen to angiotensin, lowering blood pressure.

Sulfanilamide Antibiotics

Act as a competitive inhibitor to enzymes in the biosynthetic pathways for converting PABA into folic acid in bacteria.

Penicillin

Inhibits bacterial transpeptidase, weakening the bacterial cell wall.

Enzymes in Clinical Diagnosis

Increased plasma levels of these enzymes may indicate tissue damage.