Govt. Exams
Entrance Exams
Vitamin K-dependent carboxylation of glutamate residues in prothrombin and other clotting factors creates γ-carboxyglutamate residues that coordinate Ca2+ ions, essential for binding to phospholipid membranes and clotting cascade progression.
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.
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.
Valine, with its branched nonpolar side chain, frequently appears in beta-sheets where it can form hydrophobic interactions and van der Waals contacts that stabilize the sheet structure.
Disulfide bonds (S-S) between cysteine residues form cross-links that stabilize the tertiary structure (within a protein) and quaternary structure (between subunits), particularly important in extracellular proteins.
Heat or chemical denaturants disrupt hydrogen bonds and hydrophobic interactions, affecting secondary (alpha-helix, beta-sheet) and tertiary (3D fold) structures before affecting primary structure (peptide bonds).
Digestive enzymes are synthesized as inactive zymogens (e.g., pepsinogen, trypsinogen) and are activated by proteolytic cleavage in the appropriate compartments (stomach, small intestine).
