Govt. Exams
Entrance Exams
DNA ligase catalyzes the formation of phosphodiester bonds between adjacent DNA strands. In prokaryotes, it uses NAD+ as the energy source, while in eukaryotes, ATP is used. This is essential for DNA replication, repair, and recombination.
Peptidyl transferase activity is catalyzed by the 23S rRNA (in prokaryotes) or 28S rRNA (in eukaryotes) component of the ribosome. This ribozyme catalyzes the formation of the peptide bond between the incoming aminoacyl-tRNA and the growing polypeptide chain.
Turnover number (kcat = Vmax/[E]total) represents the number of substrate molecules converted to product per enzyme molecule per unit time at maximum velocity. It indicates catalytic efficiency when substrate is saturating.
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.
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.
Transferases catalyze the transfer of functional groups (e.g., methyl, phosphoryl, amino) from one substrate to another. Examples include kinases, methyltransferases, and transaminases.
Km (Michaelis constant) is defined as the substrate concentration at which v = Vmax/2. It provides insight into enzyme-substrate affinity; lower Km indicates higher affinity.
Amylase is a hydrolase enzyme that catalyzes the hydrolysis of alpha-1,4-glycosidic bonds in starch, converting it into sugars. Both salivary and pancreatic amylases perform this function.
Leucine is a nonpolar, hydrophobic amino acid that tends to cluster in the protein interior away from the aqueous environment, while polar and charged residues prefer the surface.
Enzyme specificity arises from the precise three-dimensional arrangement of amino acid residues in the active site, which determines substrate recognition and binding through complementary fit.
