Enzymes: Structure, Classification, Kinetics, and Regulation

Comprehensive flashcards covering enzyme structure, cofactors, kinetics, EC classification, inhibition mechanisms, diagnostic uses, and regulation.

What are enzymes, and by how much do they typically accelerate chemical reaction rates?

Enzymes are macromolecules that catalyze chemical reactions in the body by lowering the activation energy, increasing reaction rates by a factor of $10^6\text{ to }10^{12}$ without being consumed in the overall process.

What are ribozymes?

Ribozymes are non-protein biological catalysts made of ribonucleic acids (RNA) that break and form covalent bonds in nucleic acids, cutting or joining RNA strands with high sequence specificity.

In detergent technology, which enzyme is utilized to degrade fat and oil stains at low temperatures?

Lipases, which degrade fat and oil into fatty acids and glycerine.

What is the primary cleaning action of cellulases when used in laundry detergents?

Cellulases hydrolyze damaged (amorphous) cellulose fibrils into saccharides and sugar, resulting in the removal of fluff.

In baking applications, what substrate does xylanase act upon, and what benefits does it provide?

Xylanase acts on non-starch polysaccharides to provide dough conditioning, volume, and softness.

Which plant cysteine proteases are used as meat tenderizers?

Papain (from papaya), zingibain (from ginger), bromelain (from pineapple), actinidin (from kiwi), and ficin (from fig).

Elevated levels of which diagnostic enzyme are indicative of a heart attack?

Creatine phosphokinase.

Which enzyme is clinically measured as a diagnostic marker for prostate cancer?

Acid phosphatase.

How does the antibiotic penicillin destroy bacterial cells?

Penicillin inhibits the enzyme responsible for synthesizing bacterial cell walls, thereby destroying the bacterium.

What physiological role does angiotensin-converting enzyme (ACE) play, and why are ACE inhibitors prescribed?

ACE causes blood vessels to narrow and elevates blood pressure; ACE inhibitors are prescribed to prevent ACE's synthesis from its zymogen, lowering blood pressure.

What is the structural difference between a simple enzyme and a conjugated enzyme?

A simple enzyme consists entirely of amino acid units, whereas a conjugated enzyme consists of a protein portion and a non-protein portion.

What is the inactive protein component of a conjugated enzyme called?

Apoenzyme (or proenzyme).

In a conjugated enzyme, what distinguishes a cofactor from a coenzyme?

A cofactor is an inorganic non-protein component (such as iron, zinc, or copper), while a coenzyme is an organic non-protein component (often derived from B vitamins or NAD).

What constitutes a holoenzyme?

A holoenzyme is the complete, active catalytic unit formed by the combination of an apoenzyme with its cofactor or coenzyme ($\text{Apoenzyme} + \text{Cofactor/Coenzyme} = \text{Holoenzyme}$).

What are the substrate and products of the enzyme urease?

The substrate is urea, and the reaction products are $\text{NH}_3$ and $\text{CO}_2$.

How does the Lock-and-Key Model describe enzyme specificity?

It states that the active site is a rigid cavity whose geometric shape exactly matches that of the substrate prior to binding.

How does the Induced Fit Model describe the interaction between an enzyme and its substrate?

It assumes that the enzyme is partially flexible and adjusts the shape of its active site upon substrate binding, with the substrate actively determining the final conformation.

What broad type of chemical reaction is catalyzed by oxidoreductases (EC 1)?

Oxidation-reduction reactions, specifically catalyzing the transfer of electrons or hydrogen between two substrates.

What is the key catalytic difference between a kinase and a phosphorylase?

A kinase transfers a phosphate group from ATP to a specified molecule, whereas a phosphorylase transfers a phosphate group from an inorganic phosphate ($\text{HPO}_4$) to a substrate.

What reaction mechanism defines hydrolases (EC 3)?

Hydrolases break single bonds in esters, carbohydrates, and proteins by adding the elements of water.

How do lyases (EC 4) differ functionally from hydrolases?

Lyases remove functional groups from substrates through non-hydrolytic mechanisms, often forming a double bond, or catalyze the addition of groups to a double bond.

What reaction is catalyzed by isomerases (EC 5)?

The interconversion of stereoisomers and structural isomers.

What reaction type defines ligases (EC 6)?

The joining of two molecules coupled with the cleavage of a phosphate anhydride bond in ATP, effectively removing the elements of water to create a single bond.

What is the functional difference between a cosubstrate and a prosthetic group?

A cosubstrate is loosely bound to an enzyme and dissociates in an altered form during the catalytic cycle (e.g., ATP, $\text{NAD}^+$, CoA), whereas a prosthetic group is permanently or tightly bound to the protein throughout the cycle (e.g., FAD, FMN, biotin).

Which vitamin serves as the precursor for thiamine pyrophosphate (TPP), and what chemical group does TPP transfer?

TPP is derived from thiamine and transfers aldehyde or keto groups (e.g., in transketolase reactions).

How does a competitive inhibitor decrease enzyme activity?

It possesses a shape and structure similar to the substrate, enabling it to compete for and occupy the enzyme's active site, thereby preventing the true substrate from binding.

What is the mechanism of action of the anti-obesity drug Orlistat?

Orlistat functions as a competitive inhibitor by binding to the active site of pancreatic lipase, reducing dietary fat absorption by $50\%$.

How does a non-competitive inhibitor prevent catalytic activity?

It binds to a site other than the active site and alters the tertiary structure of the enzyme, eliminating its catalytic effectiveness even if the substrate binds.

What is the typical optimal temperature for enzyme activity in the human body?

Around $40\,^\circ\text{C}$.

What is feedback inhibition in biochemical pathways?

A regulatory mechanism where the end product of a multi-step sequence binds to an allosteric site on the pathway's first enzyme, inhibiting its activity when product concentration is high.

What is a zymogen, and how is it converted into an active enzyme?

A zymogen (or proenzyme) is an inactive precursor enzyme that becomes active through the irreversible cleavage of one or a few peptide bonds.

What biological phenomenon is represented by this diagram of lactate dehydrogenase comprising varying combinations of H and M subunits?

Isozymes, which are enzymes that catalyze the same chemical reaction but differ in subunit composition, amino acid sequence, and catalytic efficiency.