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  Section: Genetics » Chemistry of the Gene » Synthesis, Modification and Repair of DNA
 
 
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Mitochondrial DNA replication and D-loops

 
     
 
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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


Mitochondrial DNA replication and D-loops.
In some animal cells (vertebrates), D-loops have been observed in replicating mitochondrial DNA (mtDNA). With the help of radioactive label, the fate of these D loops was studied. It could be shown that D loops represent early stages of DNA replication in mitochondria. The replication model based on D-loop is shown in Figure 26.32. The twist in supercoiled duplex is transiently relieved so that a new strand can be initiated at a fixed point, using one of the two strands. The other strand, which is not copied, balloons out as D-loop and can be seen in electron microscope at a later stage. The replication starts later on displaced single stranded D-Ioop. In this manner replication is unidirectional until about two third of one strand (H-strand) is already synthesized. About 100 minutes are needed for completion of mtDNA replication, and DNA loops in various stages of replication can be seen at a given time.
 
Model for replication of mitochondrial DNA based on D-loop; D-Ioop found at A, is extended in B, where replication takes place on inner strand. Replication on displaced strand forming D-Ioop starts later as shown in C.
Fig. 26.32. Model for replication of mitochondrial DNA based on D-loop; D-Ioop found at A, is extended in B, where replication takes place on inner strand. Replication on displaced strand forming D-Ioop starts later as shown in C.

 
     
 
 
     




     
 
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