4 public questions tagged with this topic.
The enzyme-substrate complex forms when an enzyme binds to its substrate, facilitating the reaction.
Ref: NCERT Class 11 Biology Chapter 9: Biomolecules Enzymes - Properties Classification and Cofactors
PylD finalizes pyrrolysine formation acting as NAD-dependent dehydrogenase or oxidase converting N6-(3-methylornithyl)-lysine intermediate into pyrrolysine via oxidation at epsilon position generating amino aldehyde that spontaneously cyclizes forming imine bond of pyrroline ring. Enzyme releases ammonia and water producing L-pyrrolysine with defined stereochemistry at C2 and C4 recognized by PylRS active site hydrophobic pocket. PylD possesses Rossmann-fold nucleotide-binding domain coordinating NAD cofactor similar to ornithine cyclodeaminases. Oxidation-driven ring closure logic elegantly converts linear pseudopeptide into heterocyclic amino acid, completing pathway from simple lysine precursors and providing selective advantage for methylamine-dependent methanogenesis under anaerobic conditions encountered environmentally.
Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 3: PylD Oxidase and Cyclization to Pyrrolysine
The enzyme undergoes a conformational change upon binding is the correct choice because it does not accurately describe or belong to the category addressed in this question. In the context of Enzymes Basics, the other options (The substrate fits perfectly into the enzyme’s active site, This model explains high specificity of enzymes, and It was proposed by Emil Fischer) are all valid and well-established concepts. The enzyme undergoes a conformational change upon binding is either unrelated to the topic, describes a different biological process, or represents a common misconception. Questions framed as 'which is NOT' require students to identify the exception among otherwise correct statements, demanding comprehensive knowledge of the topic rather than recognition of a single fact.
Ref: Lehninger Principles of Biochemistry, Nelson & Cox, 8th Ed., Ch. 6
Daniel Koshland is the accurate response regarding enzymatic activity or regulation described in this question. Enzymes are biological catalysts that accelerate reactions by lowering activation energy through specific substrate binding and transition state stabilization. In the context of Enzymes Basics, Daniel Koshland plays a specific catalytic or regulatory role determined by its active site configuration and mechanism of action. The other options (Emil Fischer, Michaelis and Menten, and Linus Pauling) are either different enzymes with distinct substrate specificities, act through different mechanisms, or are involved in separate metabolic pathways.
Ref: Lehninger Principles of Biochemistry, Nelson & Cox, 8th Ed., Ch. 6
