Chapter 19: Enzymes and Vitamins

Flashcards covering key vocabulary terms and definitions related to enzymes, enzyme function, regulation, and the role of vitamins and minerals as presented in the lecture notes from Chapter 19.

Enzyme

A protein that functions as a catalyst for a biological reaction.

Catalysis by Enzymes

The process by which enzymes decrease the time of a reaction to reach equilibrium by lowering the activation energy without altering the energy or equilibrium of the reaction.

Active Site

A pocket on an enzyme that has a complementary shape and physiochemical property necessary to bind and catalyze a reaction.

Substrate

The reactant in an enzyme reaction that produces a product.

Specificity (Enzyme)

The characteristic of an enzyme that allows it to act on very few to only one specific substrate.

Stereochemistry (Enzyme Specificity)

Enzyme specificity with respect to stereochemistry, where if a substrate is chiral, an enzyme catalyzes the reaction for only one enantiomer.

Turnover Number

The maximum number of substrate molecules converted to product by one molecule of enzyme per unit time (second).

Cofactor

A non-protein molecule associated with an enzyme that is essential for enzyme activity, which can represent a metal ion or a coenzyme.

Metal Ion (Cofactor)

An inorganic (no carbon) type of cofactor required by some enzymes for activity.

Coenzyme

An organic molecule that functions as an enzyme cofactor.

Vitamins (as coenzymes)

Certain dietary organic coenzymes necessary to maintain proper metabolism because humans cannot synthesize them.

Enzyme Nomenclature

System where most enzyme names end with '-ase,' with the first part identifying the substrate and the second part identifying the enzyme class.

Oxidoreductases

Enzymes that catalyze oxidation-reduction reactions of substrate molecules, most commonly addition or removal of an oxygen or hydrogen.

Oxidases

A subclass of oxidoreductases that catalyze oxidation (adds one oxygen) to a substrate.

Reductases

A subclass of oxidoreductases that catalyze reduction (adds two hydrogens) to a substrate.

Dehydrogenases

A subclass of oxidoreductases that catalyze dehydrogenation (removal of two H hydrogens) from a substrate.

Transferases

Enzymes that catalyze the transfer of a group from one molecule to another molecule.

Amino Transaminases

A subclass of transferases that transfer an amino group between substrates.

Kinases

A subclass of transferases that transfer a phosphate group from adenosine triphosphate (ATP) to produce adenosine diphosphate (ADP) and a phosphorylated product.

Hydrolases

Enzymes that catalyze the hydrolysis of substrates, breaking a bond with an addition of water.

Lipases

A subclass of hydrolases that degrade triacylglycerol into glycerol and 3 fatty acids.

Proteases

A subclass of hydrolases that degrade proteins into peptides and/or amino acids.

Amylases

A subclass of hydrolases that degrade starch into glucose.

Nucleases

A subclass of hydrolases that degrade deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) into nucleotides.

Isomerases

Enzymes that catalyze the isomerization (rearrangement of atoms) of a substrate into a product.

Lyases

Enzymes that catalyze the addition of a small molecule (H2O, CO2, or NH3) to a molecule with a double bond or the reverse reaction.

Decarboxylases

A subclass of lyases that catalyze the removal of CO2.

Deaminases

A subclass of lyases that catalyze the removal of NH3.

Dehydratases

A subclass of lyases that catalyze the removal of H2O.

Hydratases

A subclass of lyases that catalyze the addition of H2O.

Ligases

Enzymes that catalyze the bonding together of two substrate molecules, usually requiring the release of energy by hydrolysis of ATP.

Synthetases

A subclass of ligases that catalyze the formation between two substrates using energy in the form of ATP.

Carboxylases

A subclass of ligases that catalyze the formation of a bond between CO2 and a substrate using energy in the form of ATP.

Lock and Key Model

A model describing enzyme-substrate interaction where the enzyme is the lock and the substrate is a key that must fit exactly into the lock for the enzyme to catalyze the reaction.

Induced-Fit Model

A model describing enzyme-substrate interaction where the enzyme has a flexible active site capable of changing shape as the substrate enters.

Proximity Effect

An enzyme function step involving bringing substrate(s) and catalytic site(s) together in the exact manner.

Distance-Orientation Effect

An enzyme function step involving holding substrate(s) at the exact distance and exact orientation for a reaction.

Catalytic Effect

An enzyme function step involving providing the exact enzyme functional groups required for catalysis.

Energy Effect

An enzyme function step involving lowering the energy barrier of the reaction by providing an exact strain of substrate bonds.

Enzyme Saturation

The state where an enzyme's active sites are physically saturated with substrate, and additional substrate has no further effect on the reaction rate.

Enzyme Denaturation

The process where rising temperature disrupts non-covalent bonds between protein R groups in an enzyme, destroying the active site.

Optimum pH

The specific pH at which an enzyme demonstrates its highest catalytic activity.

Activation of an Enzyme

Any process that initiates or increases an enzyme's function.

Inhibition of an Enzyme

Any process that prevents or decreases an enzyme's function.

Reversible Competitive Inhibition

A type of inhibition where a reversible inhibitor competes with the substrate for an enzyme's active site.

Reversible Uncompetitive Inhibition

A type of inhibition where a reversible inhibitor binds to the enzyme-substrate complex, but not the active site, making the reaction less efficient.

Irreversible Inhibition

A type of inhibition where the enzyme reaction cannot occur because the substrate cannot bind in the active site again, often due to permanent covalent binding of an inhibitor.

Allosteric Control

An interaction where the binding of a regulator molecule at one site of a protein affects its ability to bind a substrate at the active site.

Allosteric Enzyme

An enzyme controlled by the binding of a regulator (activator or inhibitor) at a location other than the active site.

Negative Regulator (Allosteric)

A molecule that changes an active site so that the enzyme can no longer bind the substrate, decreasing enzyme function.

Positive Regulator (Allosteric)

A molecule that changes an unavailable active site to an available active site, permitting an enzyme to catalyze a reaction.

Feedback Control

Regulation of an enzyme by a product resulting from a reaction occurring later in a metabolic pathway, affecting a known regulatory enzyme positioned first in that pathway.

Zymogen

An inactive enzyme (also called proenzyme) that becomes an active enzyme after cellular and biochemical modification, typically by cleaving a portion of the molecule.

Proenzyme

An inactive form of an enzyme, also known as a zymogen, that requires a chemical reaction to remove a portion to become active.

Covalent Modification (Enzyme Regulation)

A mode of enzyme regulation involving the removal or addition of a covalently bonded portion to an enzyme, such as phosphorylation or de-phosphorylation.

Kinase enzymes

Enzymes that catalyze the addition of a phosphoryl group (phosphorylation), supplied by ATP, to serine, tyrosine, or threonine residues.

Phosphatase enzymes

Enzymes that catalyze the removal of a phosphoryl group (de-phosphorylation).

Genetic Control (Enzyme Regulation)

Regulation of enzyme synthesis (and thus concentration) through genetic expression.

Vitamin

An organic molecule, essential in trace amounts, that must be acquired from the diet because it is not synthesized by the human body.

Water-Soluble Vitamins

Vitamins found in the aqueous environment inside cells, containing -OH, -COOH, or other polar groups that allow them to remain water soluble.

Fat-Soluble Vitamins

Vitamins (A, D, E, and K) that are stored in fat deposits and have not been identified to serve as coenzymes.

Antioxidant

A substance that prevents oxidation by reacting with an oxidizing substance, such as defusing free radicals.

Free Radicals

Reactive molecular fragments with unpaired electrons that gain stability by picking up electrons from nearby molecules.

Minerals (Micronutrients)

A group of micronutrients, primarily transition group elements, necessary for proper enzyme functioning (as cofactors), as building blocks for the body, or as electrolytes.

Macro-minerals

Minerals required in daily amounts greater than 100 mg per day, including calcium, phosphorous, magnesium, potassium, sodium, chloride, and sulfur.

Micro-minerals

Transition elements required in smaller amounts, including chromium, copper, magnesium, manganese, molybdenum, selenium, and zinc.