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Subject - biology
The endosymbiotic theory states that eukaryotic cells once became larger cells by absorbing a prokaryote. Bacteria entered into a symbiotic relationship with these primitive protoeucytes1). It is postulated that chloroplasts originally descended from cyanobacteria and mitochondria from aerobic prokaryotes. The following experimental data support this theory:
- Mitochondria and chloroplasts contain circular, single-stranded DNA molecules that may be present as multiple copies. These are semiautonomous, meaning that they are dependent on molecular components that are coded in the nuclear genome.
- Both of these organelles have their own ribosomes, which are of type 70S, in agreement with those of prokaryotes. Likewise, and molecules are coded in the organelle genomes. Phylogenetic2) studies involving comparative rRNA sequence analysis also substantiate this relationship.
- Organelle protein biosynthesis is, like that of the prokaryotes, sensitive toward the elongation (German learning unit) of eukaryotic cytoplasmic 80S ribosomes (peptidyl transferase activity of the 60S subunit). chloramphenicol and streptomycin, but not cycloheximide. The latter blocks the
|1)||eucytes: the cells of a eukaryote|
|2)||phylogenesis: evolutionary biological development of a strain|
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