Govt. Exams
Entrance Exams
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).
Molecular chaperones like Hsp70 and Hsp90 help nascent proteins fold into their correct three-dimensional structure and prevent inappropriate aggregation, essential for cellular proteostasis.
Aldolase requires a Zn²⁺ cofactor as part of its active site, which is crucial for substrate binding and catalysis in aldol condensation reactions.
An alpha-helix makes 3.6 residues per turn. Each C=O of residue n forms a hydrogen bond with the N-H of residue n+4, resulting in approximately 4 hydrogen bonds per turn.
In competitive inhibition, the inhibitor competes with substrate for the active site. The apparent Km increases (appears to require more substrate to reach Vmax), but true Vmax remains unchanged because the inhibitor can be outcompeted at high substrate concentrations.
Allosteric enzymes have regulatory sites distinct from active sites and show cooperativity, resulting in sigmoidal kinetics rather than hyperbolic kinetics seen in simple enzymes.
Lipase catalyzes the hydrolysis of ester bonds in lipids. Amylase acts on carbohydrates, protease on proteins, and nuclease on nucleic acids.
