Comparing Mitochondrial, Chloroplast, and Prokaryotic Genomes

Primitive predator cells internalized bacteria that later evolved into mitochondria, forming eukaryotic cells. Photosynthetic cyanobacteria also formed symbiotic relationships with some of these eukaryotic cells and eventually developed into the chloroplast.

The present-day mitochondrial and chloroplast genomes are the remnants of these ancestral prokaryotic genomes.

Compared to mitochondrial genomes, the genomes of current day prokaryotes are large such as in Escherichia coli which contain around 5 million bps and nearly 5000 genes.

The human mitochondrial genome is almost 17,000 bps long and contains 37 genes - whereas the mitochondrial genome of Arabidopsis thaliana, a flowering plant, has over 350,000 bps but contains only 57 genes.

Compared to current day cyanobacterial genomes, like the Synechocystis genome which has around 3.5 million bps and carries approximately 3200 genes, the chloroplast genome among terrestrial plants has up to 200,000 bps contains 120-135 genes. 

Even though they are much smaller, both mitochondrial and chloroplast genomes are similar to the prokaryotic genome in several ways. Their DNA does not associate with histone proteins and is usually circular and double-stranded, similar to that of bacterial plasmids. 

Compared to the mitochondrial genome, the chloroplast genome more closely resembles the prokaryotic genome. Both chloroplast and prokaryotic genomes have quite similar DNA sequences for transcription promoters and terminators.

Additionally, animal mitochondrial genomes are generally smaller than the mitochondrial genome in plants, as both chloroplast and plant mitochondrial genomes have introns that are absent in most animal mitochondrial genomes.