Enzymes and Cellular Macromolecules

Comprehensive practice flashcards covering enzyme mechanics, classification, regulation, and the properties of cellulose based on the provided lecture notes.

To which group of macromolecules does cellulose belong?

Polysaccharides

Cellulose is a linear polymer of which specific monomers?

eta ext{-D-glucose}

What characterizes the 'Metastable State' in cellular reactions?

A state where thermodynamically feasible reactions (like the hydrolysis of ATP with a $ext{ } ext{\Delta}G = -7.3 ext{ kcal/mol}$) do not proceed at an appreciable rate because they lack sufficient activation energy.

Why is increasing temperature not a viable way for cells to increase reaction rates?

Cells are isothermal, meaning they must maintain a constant temperature for homeostasis.

What are the three basic properties shared by all catalysts?

1. They increase reaction rates by lowering the $E_A$ required; 2. They form transient, reversible complexes with substrate molecules; 3. They change the rate of equilibrium achievement, but not the position of the equilibrium.

What is the name for RNA molecules that possess catalytic activity?

Ribozymes

What is the function of the enzyme Ribonuclease P?

It cleaves transfer RNA (tRNA) precursors to yield functional RNA molecules.

Match the enzyme class 'Oxidoreductases' to its reaction type.

Oxidation-reduction reactions (electron transfer)

Match the enzyme class 'Hydrolases' to its reaction type.

Hydrolytic cleavage of one molecule into two molecules

Match the enzyme class 'Ligases' to its reaction type.

Joining of two molecules to form a single molecule

What defines the 'active site' of a protein enzyme?

A characteristic cluster of amino acids forming a groove or pocket, resulting from the three-dimensional folding of the protein, where substrates bind and catalysis occurs.

What are prosthetic groups in the context of enzymes?

Nonprotein cofactors such as metal ions or small organic molecules (coenzymes) needed for catalytic activity.

What is the optimal temperature for a typical human enzyme versus a thermophilic bacterium enzyme?

Human enzyme: $ext{approximately }37 ext{ }^ ext{\circ} ext{C}$; Thermophilic bacterium: $ext{approximately }75 ext{ }^ ext{\circ} ext{C}$

What are the approximate pH optima for the enzymes pepsin and trypsin?

Pepsin (stomach): $ext{approximately }2.0$; Trypsin (intestinal): $ext{near }8.0$

What observation supports the induced-fit model over the lock-and-key model?

X-ray diffraction shows that enzymes bound to a substrate have different shapes from those same enzymes when the substrate is absent.

What are the three common mechanisms of substrate activation?

1. Bond distortion; 2. Proton transfer; 3. Electron transfer

What is the difference between irreversible and reversible enzyme inhibitors?

Irreversible inhibitors bind covalently and cause permanent loss of activity; reversible inhibitors bind noncovalently and can dissociate.

How does a competitive inhibitor function?

It binds to the active site and prevents substrate binding, making its effectiveness dependent on the concentration of the substrate.

How does a noncompetitive inhibitor function?

It binds to a site other than the active site, distorting the enzyme's shape and reducing catalytic activity independent of substrate concentration.

What is allosteric regulation?

A control mechanism where enzymes shift between two conformations (high and low affinity) based on the binding of molecules to an allosteric site.

What is feedback (end-product) inhibition?

A process where the final product of an enzyme pathway negatively regulates an earlier step in that same pathway.

Name three types of reversible covalent modifications used to regulate enzymes.

Phosphorylation/Dephosphorylation, Methylation/Demethylation, and Acetylation/Deacetylation

What is a zymogen?

An inactive form of an enzyme that is activated by irreversible proteolytic cleavage (the removal of part of the polypeptide chain).