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Section: Genetics » Chemistry of the Gene » Synthesis, Modification and Repair of DNA
 
 
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  Rolling circle model of DNA replication
 
     
 
Content
⇒ Chemistry of the Gene 2.  Synthesis, Modification and Repair of DNA
⇒ DNA replication: general features 
⇒ Semi-conservative DNA replication in E. coli
⇒ Semi-conservative replication of chromosomes in eukaryotes
⇒ Semi-discontinuous DNA replication
⇒ Unidirectional and bidirectional DNA replication
⇒ RNA primers in DNA replication
⇒ Regulation of DNA replication by anti-sense RNA primer
⇒ Prokaryotic DNA polymerases
⇒ Eukaryotic DNA polymerases
⇒ Replicons for DNA replication
⇒ DNA replication in prokaryotes 
⇒ Experimental approaches for the study of DNA replication
⇒ Initiation of DNA replication
⇒ Elongation of DNA chain
⇒ Replication fork movement
⇒ Termination of DNA replication
⇒ DNA replication in eukaryotes 
⇒ DNA replication and cell cycle
⇒ Replication origins and initiation of DNA replication (cis and trans-acting elements)
⇒ Comparison of initiation of DNA replication with transcription initiation
⇒ Different steps involved in eukaryotic DNA replication
⇒ Synthesis of telomeric DNA by telomerase
⇒ Models of DNA replication
⇒ Replication fork model
⇒ Rolling circle model of DNA replication
⇒ Mitochondrial DNA replication and D-loops
⇒ RNA directed DNA synthesis (reverse transcription)
⇒ DNA modification and DNA restriction
⇒ DNA repair
⇒ Excision repair systems in E. coli
⇒ An SOS repair system in E. coli
⇒ DNA repair and genetic diseases in humans


Rolling circle model of DNA replication
Alternative mechanism has been suggested for the replication of circular DNA and this is called rolling circle mechanism, which explains multiplication of many viral DNAs and also explains DNA replication during bacterial mating. One of the evidences in support of this model is the observation of long chains of polynucleotides which could measure several times the contour length of circular DNA. In this mode, due to nicking in one of the two strands, one strand becomes a polynucleotide with two ends, one end having 3'-OH group, the other having 5'p group. DNA synthesis starts by adding bases at 3'-OH end, displacing the 5' end, which rolls out as a free tail, and is then copied in 5'→3' direction in small segments using fresh enzymes system. These tails thus become double stranded and give rise to a circular DNA later on. A possible mechanism of replication of circular DNA using rolling circle model is shown in Figure 26.31.
 
Model for replication of circular double helical DNA, based on rolling of DNA circle following a nick formation due to endonuclease.
Fig. 26.31. Model for replication of circular double helical DNA, based on rolling of DNA circle following a nick formation due to endonuclease.

 
     






     
     
 
 
     
 
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