Mitochondrial DNA replication and D-loops

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.
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.