Abstract: Symbiogenesis, or endosymbiotic theory, is an evolutionary theory that explains the origin of eukaryotic cells from prokaryotes. It states that several key organelles of eukaryotes originated as a symbiosis between separate single-celled organisms. According to this theory, mitochondria, plastids (for example chloroplasts), and possibly other organelles representing formerly free-living bacteria (prokaryotes) were taken inside another cell as an endosymbiont around 1.5 billion years ago. According to Endo-symbiotic theory, mitochondrion and chloroplast has originated from bacteria. But if we compare the genomes of bacteria, chloroplast and mitochondrion there is a difference in the protein synthesizing machineries of all the three structures indicating that they have origination is some thing different from endo-symbiotic theory.