During DNA replication, Okazaki fragments are seen in relation to:
Ans: B (Lagging strand) Ref: Harpers Illustrated Biochemistry, 29th editionExplanation:DNA SYNTHESIS and REPLICATIONSteps Involved in DNA Replication:1. Identification of the origins of replication2. Unwinding (denaturation) of dsDNA to provide an ssDNA template3. Formation of the replication fork4. Initiation of DNA synthesis and elongation5. Formation of replication bubbles with ligation of the newly synthesized DNA segments6. Reconstitution of chromatin structureClasses of Proteins Involved in ReplicationProteinFunctionDNA polymerasesDeoxynucleotide polymerizationHelicasesProcessive unwinding of DNATopoisomerasesRelieve torsional strain that results from helicase-induced unwindingDNA primaseInitiates synthesis of RNA primersSingle-strand binding proteinsPrevent premature reannealing of dsDNADNA ligaseSeals the single strand nick between the nascent chain and Okazaki fragments on lagging strandThe Origin of ReplicationAt the origin of replication tori), there is an association of sequence-specific dsDNA-binding proteins with a series of direct repeat DNA sequences.The interaction of proteins with ori defines the start site of replication and provides a short region of ssDNA essential for initiation of synthesis of the nascent DNA strand.Single-stranded DNA-binding proteins (SSBs) stabilize this complex.Formation of the Replication ForkA replication fork consists of four components that form in the following sequence:The DNA helicase unwinds a short segment of the parental duplex DNAA Primase initiates synthesis of an RNA molecule that is essential for priming DNA synthesisThe DNA polymerase initiates nascent, daughter strand synthesisSSBs bind to ssDNA and prevent premature reannealing of ssDNA to dsDNA.DNA polymerases only synthesize DNA - in the 5' to 3' direction, and only one of the several different types of polymerases is involved at the replication fork.Because the DNA strands are antiparallel, the polymerase functions asymmetrically.On the leading (forward strand, the DNA is synthesized continuously.On the lagging (retrograde) strand, the DNA is synthesized in short fragments, the so- called Okazaki fragments.Several Okazaki fragments (upto 250) must be sequentially synthesized for each replication fork.To ensure that this happens, the helicase acts on the lagging strand to unwind dsDNA in a 5' to 3' direction.The helicase associates with the primase to afford the latter proper access to the template.This al lows the RNA primer to be made and. in turn, the polymerase to begin replicating the DNA.This is an important reaction sequence since DNA polymerases cannot initiate DNA synthesis de novo. The mobile complex between helicase and primase has been called a primosome.As the synthesis of an Okazaki fragment is completed and the polymerase is released, a new primer has been synthesized.The same polymerase molecule remains associated with the replication fork and proceeds to synthesize the next Okazaki fragment.
Leading strand
Lagging strand
Both "
Helicase
DNA Replication 