Besides DNA a mitochondrion has RNA and its ribosomes also. Thus a complete protein synthesizing maschinary is present in mitochondria. The ribosomes of mitochondria are small i.e., 55−60S type, with a large subunit of 40S and a small subunit of 30S. The large subunit contain 16−17S and 5Sr−RNA and the small subunit 12−13Sr−RNA. 70S type of ribosomes are found in prokaryotic cell. They are composed of large subunit of 50S(23S+5Sr−RNA) and small subunit of 30S(16Sr−RNA).