Question

Name two cell organelles that contain their own dna and ribosomes

Answer 1

Plastids and mitochondria.

Answer 2

• The two cell organelles which contain their own genetic material are namely: Mitochondria (present in all eukaryotic cell) and chloroplast (present in organisms belonging to Plant Kingdom only).

• Therefore these organelles are called semi-autonomous organelles.

• The genetic material of these organelles are called extra-nuclear genetic material or extra-nuclear chromosomes.

• The genetic material (DNA) of these organelles also divide during cell division.

• Mitochondrial DNA also plays an important role during development of embryo as during fertilization male gamete only contributes nucleus but the female gamete contributes nucleus (which fuses with nucleus of male gamete) as well as cytoplasm (which contains mitochondrial DNA or maternal DNA or mtDNA). Therefore mitochondrial DNA of all organisms are more similiar compared to nuclear DNA.

• Chloroplast DNA is called cpDNA. It is also referred to as plastome with reference to other plastids. Chloroplast DNA is also maternally inherited.

• There is a theory called endosymbiotic theory: According to that mitochondria and chloroplast were actually prokaryotes (bacteria) during anaerobic conditions of early earth. Some bigger cells engulfed them, but they did not lose their ability to synthesize their own DNA and got better and safe environment to live and in this condition started aerobic respiration and due to this only environment became aerobic. Gradually they lost their ability to live freely and became part of the cell. It is believed that Mitochondrium evolved from alpha proteobacterium, Rickettsia prowazekii and chloroplast evolved from cyanobacterium called Prochloron.