8 public questions tagged with this topic.
Autonomous replication refers to the ability of a plasmid to replicate independently of the host chromosome.
Ref: NCERT Class 12 Biology Chapter 9: Biotechnology: Principles and Processes Bioreactors and Downstream Processing
Autonomous replication allows plasmids to multiply independently of the host chromosome.
Ref: NCERT Class 12 Biology Chapter 9: Biotechnology: Principles and Processes Competent Host and Gene Transfer Methods
DNA polymerase requires an RNA primer to initiate replication because it cannot start synthesis de novo.
Ref: NCERT Class 12 Biology Chapter 5: Molecular Basis of Inheritance Post-Transcriptional Modifications - Capping Splicing Polyadenylation
RNA dependent RNA polymerase synthesizes RNA polymer using RNA template, reaction central to life cycles of RNA viruses. Unlike DNA-dependent RNA polymerase transcribing DNA to RNA, RdRp reads single-stranded or double-stranded RNA via complementary base pairing producing new RNA strand. Active site contains conserved GDD motif coordinating magnesium ions catalyzing phosphodiester formation. Host mammalian cells generally lack RdRp except for limited RNA interference amplification pathways, whereas most RNA viruses encode own enzyme for replication. Enzymatic activity often membrane-associated, lacking proofreading, contributing to high mutation rates among RNA viral genomes during propagation.
Ref: Lodish Chapter 8: RNA dependent RNA polymerase uses RNA template definition; Fields Virology Chapter 6 RdRp mechanism
Okazaki fragment synthesis inevitably leaves gaps between fragments after primer removal. Pol I synthesizes DNA to fill those short single-strand gaps using upstream 3' OH as primer ensuring precise replacement of RNA with DNA in 5' to 3' direction. Once filling complete, adjacent fragments remain connected by single phosphodiester nick because polymerase cannot create final bond between 3' hydroxyl and 5' phosphate. DNA ligase using NAD+ cofactor in bacteria hydrolyzes to close nick forming continuous phosphodiester backbone. Requirement for both enzymes couples gap filling and final ligation.
Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 5: Joining Okazaki fragments by Pol I and DNA ligase
E. coli possesses five DNA polymerases, but bulk chromosome duplication is performed exclusively by DNA polymerase III holoenzyme. Pol III exists as dimeric asymmetric complex containing alpha polymerase, epsilon proofreading exonuclease, theta stabilizer, tau dimerization, beta sliding clamp, and gamma clamp loader plus chi psi subunits. Its very high processivity exceeding 500 kilobases and rapid rate near 750 nucleotides per second allows simultaneous leading and lagging strand synthesis within replisome. Pol I mainly fills gaps and removes primers while Pol II, IV, V function primarily in repair.
Ref: Lewin Benjamin, Genes XII, Chapter 13: E. coli replicase - DNA polymerase III holoenzyme composition
At replication fork, leading strand synthesis runs continuously toward fork movement with same polarity as unwinding. Because duplex opens progressively ahead, polymerase can track helicase without interruption. DNA polymerase requires pre-existing 3' OH for extension, supplied by primase only once at origin. Single RNA primer about 10 nucleotides synthesized by DnaG provides initial hydroxyl for Pol III, thereafter Pol III extends uninterrupted for hundreds of kilobases. Lagging strand oriented opposite cannot do this and therefore needs repeated priming generating Okazaki fragments.
Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 5: Leading strand continuous synthesis and priming
Removing supercoiling stress accurately defines or describes the concept asked in this question. Within DNA, precise definitions and terminology are essential for clear scientific communication. The other options (Catalyzing DNA replication, Breaking phosphodiester bonds permanently, and Synthesizing RNA primers) either describe related but distinct concepts, use incorrect terminology, or confuse similar-sounding terms that have different scientific meanings. A thorough understanding of exact definitions helps distinguish between closely related biological concepts and is crucial for competitive examinations.
Ref: Molecular Biology of the Gene, Watson et al., 7th Ed.
