Govt Exams
Leucine is a nonpolar, hydrophobic amino acid with an isobutyl side chain. Serine and threonine are polar uncharged, while aspartate is acidic and polar.
Denaturation is disruption of non-covalent interactions (hydrogen bonds, hydrophobic interactions, ionic bonds) that maintain higher-order structures. Peptide bonds (primary structure) remain intact. Some proteins can refold (renature) if conditions permit, as demonstrated by Anfinsen's ribonuclease experiments.
The isoelectric point is the pH at which the net charge on the protein is zero, resulting in minimum solubility and maximum precipitation.
Proteases are endopeptidases and exopeptidases that hydrolyze peptide bonds in proteins. Amylase acts on carbohydrates, lipase on fats, and nuclease on nucleic acids.
Hemoglobin has quaternary structure consisting of 2 α-globin and 2 β-globin subunits held together by non-covalent interactions.
Leucine has a nonpolar, hydrophobic isopropyl side chain. Serine and asparagine are polar, while lysine is positively charged.
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.