Some mitochondrial DNAs possess several D loops, reflecting the use of multiple origins. The same mechanism is employed in chloroplast DNA, where (in complex plants) there are two D loops.

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#Id: 3190

#Unit 3. Fundamental Processes

To replicate mammalian mitochondrial DNA, the short strand in the D loop is extended. The displaced region of the original L strand becomes longer, expanding the D loop

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#Id: 3191

#Unit 3. Fundamental Processes

In mtDNA, The existence of D loops exposes a general principle: An origin can be a sequence of DNA that serves to initiate DNA synthesis using om strand as a Template.

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#Id: 3192

#Unit 3. Fundamental Processes

In the case of mitochondrial DNA replication, the origins for replicating the complementary strands lie at different locations

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#Id: 3193

#Unit 3. Fundamental Processes

Origins that sponsor replication of only one strand are also found in the rolling circle mode of replication.

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#Id: 3198

#Unit 3. Fundamental Processes

Errors in replication and damage to DNA have two consequences;
One is, of course, the introduction of permanent changes to the DNA (mutations), which can alter the coding sequence of a gene or its regulatory sequences.
The second consequence is that some chemical alterations to the DNA prevent its use as a template for replication and transcription