HL A2.2 Endosymbiosis Theory

Endosymbiosis theory explains eukaryotic cell complexity as arising when ancestral prokaryotic cells were engulfed by larger cells and formed permanent, mutualistic relationships.

Chloroplasts evolved from photosynthetic cyanobacteria, allowing eukaryotes to perform photosynthesis.

Mitochondria evolved from aerobic, purple bacteria that were engulfed and provided efficient ATP production via aerobic respiration.

Mitochondria and chloroplasts have double membranes: the outer membrane resembles a host vesicle, while the inner membrane resembles bacterial membranes.

They contain 70S ribosomes, the same size as bacterial ribosomes, unlike the 80S ribosomes in the eukaryotic cytoplasm.

Both mitochondria and chloroplasts contain their own single, circular DNA with no histones, like bacteria.

Mitochondria and chloroplasts divide by binary fission, not mitosis, and only arise from pre-existing organelles.

Antibiotics that inhibit bacterial protein synthesis also inhibit mitochondrial and chloroplast protein synthesis.