Govt Exams
Chymotrypsin is secreted as chymotrypsinogen. Trypsin (activated by enterokinase) cleaves a specific dipeptide from chymotrypsinogen to generate active chymotrypsin, which then undergoes autolytic cleavage for full activation.
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.
PP2A is a major serine/threonine phosphatase that plays crucial roles in reversing kinase-mediated phosphorylation. Its dysfunction is associated with various cancers, making it an important tumor suppressor enzyme.
Phenylalanine hydroxylase requires tetrahydrobiopterin (BH4) as a cofactor for the hydroxylation of phenylalanine to tyrosine. Mutations in this enzyme or BH4 synthesis lead to PKU, causing intellectual disability if untreated.
Allosteric enzymes like phosphofructokinase show cooperative binding where substrate binding at one subunit increases affinity at others. This produces an S-shaped curve rather than the hyperbolic Michaelis-Menten curve, allowing for better metabolic control.
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.
Collagen has a characteristic Gly-X-Y tripeptide repeat pattern where glycine appears at every third position. This allows tight packing in the triple helix structure. Hydroxyproline (formed by post-translational modification of proline) stabilizes the helix.
Competitive inhibitors compete with substrate for the active site, increasing apparent Km while Vmax remains unchanged. Non-competitive inhibitors bind to a site other than the active site, decreasing Vmax without changing Km.
Aconitase requires an iron-sulfur cluster [4Fe-4S] for catalyzing the isomerization of citrate to isocitrate. This is essential for its catalytic mechanism in the TCA cycle.
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.