Question

DNA is present in or which one of the following has its own DNA?
(a) Nucleus only
(b) Mitochondria only
(c) Chloroplast only
(d) All of the above

Answer 1

Hint: Some cell organelles are endosymbionts as they are supposed to have developed from an endosymbiotic mutualistic relationship. These organelles function as semi-autonomous organelles and replicate on their own whenever required.

Complete step-by-step answer:
In eukaryotic cells, besides the nucleus, the DNA is present in two other cell organelles, chloroplast, and mitochondria.

Additional Information:
Presence of the DNA in them is explained by a theory known as endosymbiotic theory. According to the theory, these two organelles were once anaerobic bacteria like prokaryotic microbes in an earlier time and got engulfed by endocytosis by the photosynthetic bacteria and aerobic bacteria where they formed a mutually beneficial relationship and evolved as chloroplast and mitochondria respectively and the parent cell developed as plant cell and animal cell respectively.
Thus, these two organelles have their own DNA which is similar to the prokaryotic DNA as it is single circular DNA unlike the double-stranded linear DNA of eukaryotes. Due to the presence of their own DNA, they function as semi-autonomous organelles and divide by binary fission whenever required. These two organelles have been shown in the figure below -

Fig.- Chloroplast

Fig.- Mitochondria

So, the correct answer is ‘All of the above’.

Note:
1. Mitochondria is a cylindrical or sausage-shaped double membranous organelle found in all the eukaryotic cells. The inner and outer membranes differ in the structure as the outer one is smooth but the inner one has enfoldings that are called cristae. The inner membrane surrounds a matrix where single circular DNA, a few RNAs, 70s ribosomes, and other components required for protein synthesis are present.
2. Chloroplasts are also double membrane-bound and are located in the cytoplasm of eukaryotic plant cells only. They absorb sunlight and using light and environmental carbon dioxide, they make food i.e. sugar for the plant cells.