Also formed are a 16S and a 12S ribosomal RNA. Although proteins and small molecules such as A TP and tRNAs can move in and out of the mitochondrion, large RNAs cannot.
Most interestingly, all mtDNAs exhibit the same basic organization of genetic information. Each contains 2 rRNA genes, 22 tRNA genes, and 13 putative protein structural genes. Five genes encode known proteins but the products and functions of the other putative genes have not yet been identified.

The entire mammalian mitochondrial genome is transcribed as one unit from a single promoter site and the giant primary transcript is then cleaved endonucleolytically to produce the individual tRNA, rRNA and mRNA molecule. Thus, the entire mtDNA is, in effect, equivalent to one operon in bacteria

Some genes actually overlap and almost every single base pair can be assigned to a gene, with the exception of the D- Loop, a region concerned with the initiation of DNA replication. In yeast cells, 10-20 percent of the cellular DNA is localized in a single mitochondrion.

Yeast mitochondria have introns and are not economical like that of mammalian mitochondria. Some suggest that the genes with introns have been originated in the nucleus and are later captured or integrated by the mitochondria. Even the genome size is five times bigger than mammalian mtDNA.