Entrance Exams
Govt. Exams
Enzyme specificity varies: absolute (one substrate only), group (substrates with similar functional groups), linkage (specific types of bonds), and stereochemical (stereoisomers). Specificity results from 3D active site structure and orientation of catalytic residues.
Alcohol dehydrogenase contains catalytic zinc that coordinates the hydroxyl group of ethanol/aldehyde substrate, activating it for hydride transfer to NAD+, and structural zinc that maintains protein stability.
Ornithine transcarbamylase (OTC) catalyzes the condensation of carbamoyl phosphate (formed by CPS I) with ornithine to form citrulline, the second step of the urea cycle. OTC deficiency is the most common urea cycle disorder.
PFK exhibits allosteric regulation where AMP/ADP (signals of low energy) activate the enzyme, while ATP/citrate (signals of high energy/biosynthesis) inhibit it by binding to allosteric sites, changing enzyme conformation.
Glycine (every third residue) provides flexibility, proline stabilizes the polyproline II helix conformation, and hydroxyproline (formed by post-translational modification) stabilizes the triple helix through additional hydrogen bonding.
Ubiquitin is a 76-amino acid protein that is conjugated to lysine residues of target proteins via E1, E2, and E3 enzymes, marking them for degradation by the 26S proteasome.
Gaucher disease results from deficiency of β-glucosidase (glucocerebrosidase), leading to accumulation of glucocerebroside in lysosomes, particularly in macrophages, spleen, and liver.
In α-helix, hydrogen bonds form between C=O and N-H groups within the same chain. In β-sheet, hydrogen bonds form between adjacent polypeptide chains running parallel or antiparallel to each other.
In competitive inhibition, the inhibitor competes with substrate for the active site, so more substrate is needed to achieve half-maximal velocity (increased apparent Km), but Vmax remains unchanged.
Km is the substrate concentration at which the reaction velocity is half of Vmax (V = Vmax/2), and it represents the affinity of enzyme for substrate. Lower Km indicates higher affinity.