zum Directory-modus

endosymbiotic theoryZoomA-Z

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:

  1. 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.
  2. Both of these organelles have their own ribosomes, which are of type 70S, in agreement with those of prokaryotes. Likewise, rRNA and tRNA molecules are coded in the organelle genomes. Phylogenetic2) studies involving comparative rRNA sequence analysis also substantiate this relationship.
  3. Organelle protein biosynthesis is, like that of the prokaryotes, sensitive toward the antibiotics chloramphenicol and streptomycin, but not cycloheximide. The latter blocks the elongation (German learning unit) of eukaryotic cytoplasmic 80S ribosomes (peptidyl transferase activity of the 60S subunit).

See also: chloroplasts , mitochondrion

1)eucytes: the cells of a eukaryote
2)phylogenesis: evolutionary biological development of a strain

Recommended Learning Units

Cell Structure and Cell OrganellesLevel 160 min.

BiochemistryBiological FundamentalsCell Morphology

Cytology is introduced by means of illustrations, animations, and a comprehensive collection of references and selected links.