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a: template, b: leading strand, c: lagging strand, d: replication fork, e: primer, f: Okazaki fragments Many enzymes are involved in the DNA replication fork. The replication fork is a structure that forms within the long helical DNA during DNA replication.
Asymmetry in the synthesis of leading and lagging strands. Okazaki fragments are short sequences of DNA nucleotides (approximately 150 to 200 base pairs long in eukaryotes) which are synthesized discontinuously and later linked together by the enzyme DNA ligase to create the lagging strand during DNA replication. [1]
During DNA replication, the replisome will unwind the parental duplex DNA into a two single-stranded DNA template replication fork in a 5' to 3' direction. The leading strand is the template strand that is being replicated in the same direction as the movement of the replication fork.
The leading strand in DNA replication is synthesized in one continuous piece moving with the replication fork, requiring only an initial RNA primer to begin synthesis. In the lagging strand, the template DNA runs in the 5′→3′ direction.
The total result is formation of two new double stranded DNA sequences that are exact copies of the original double stranded DNA sequence. [1] In terms of structure, the replisome is composed of two replicative polymerase complexes, one of which synthesizes the leading strand, while the other synthesizes the lagging strand.
GC or AT skew changes sign at the boundaries of the two replichores, which correspond to DNA replication origin or terminus. [2] [4] [5] Originally, this asymmetric nucleotide composition was explained as a different mechanism used in DNA replication between the leading strand and lagging strand.
The rate of DNA replication in a living cell was first measured as the rate of phage T4 DNA elongation in phage-infected E. coli. [18] During the period of exponential DNA increase at 37 °C, the rate was 749 nucleotides per second. The mutation rate per base pair per replication during phage T4 DNA synthesis is 1.7 per 10 8. [19]
Leading strand synthesis begins with the synthesis of a short RNA primer at the replication origin by the enzyme Primase (DnaG protein). Deoxynucleotides are then added to this primer by a single DNA polymerase III dimer, in an integrated complex with DnaB helicase. Leading strand synthesis then proceeds continuously, while the DNA is ...