Govt Exams
GroEL/GroES in prokaryotes forms a barrel-like structure that creates an isolated environment for protein folding. GroEL binds unfolded proteins using ATP hydrolysis, providing conformational assistance distinct from Hsp70's role in preventing aggregation.
Aminoacyl-tRNA synthetases achieve high fidelity through a two-step selection process: initial selection during aminoacylation and a second proofreading step (editing) that hydrolyzes incorrectly charged tRNA-amino acid complexes before they leave the enzyme.
Serine proteases have an extended substrate-binding site composed of multiple subsites (S1, S1', S2, etc.) that recognize and bind extended substrate peptides. The catalytic triad (Ser-His-Asp) performs the actual catalysis.
Turnover number (kcat) is the number of substrate molecules converted to product per enzyme molecule per unit time when the enzyme is fully saturated. It equals Vmax/[E]total.
Negative cooperativity occurs when substrate binding to one subunit decreases the affinity of other subunits for substrate, resulting in a hyperbolic (rather than sigmoidal) binding curve.
When Km >> [S], the Michaelis-Menten equation simplifies to v = (Vmax/Km)[S], making the reaction essentially first-order. The enzyme has low affinity for substrate under these conditions.
In non-competitive inhibition, both Km and Vmax are affected proportionally. On a Lineweaver-Burk plot (1/v vs 1/[S]), this results in lines with different slopes that intersect on the y-axis.
Ca²⁺ is required for enzymatic activity and is not consumed in the reaction, making it a cofactor. Many proteases require metal ions as structural or catalytic cofactors.
Tertiary structure requires secondary structure elements. Secondary structures (α-helix, β-sheet) fold into tertiary structure; one cannot exist without the other.
Apparent Km = Km(1 + [I]/Ki) = 2(1 + 1/0.5) = 2(1 + 2) = 6 mM. Competitive inhibition increases apparent Km without changing Vmax.