The Endosymbiotic Theory

Symbiosis

• close relationship between organisms of different species that live together

Endosymbiotic Theory

• some of todays eukaryotic organelles arose from free-living prokaryotes which were engulfed by a eukaryotic precursor

eukaryotic organelles which are descendants of these prokaryotes

mitochondria and chloroplasts

• mitochondria

  • energy producing bacteria was engulfed

• chloroplasts

  • photosynthetic bacteria was engulfed by an ancestral eukaryote

plastids

• double membraned organelles

• plants and algae

• manufacture and store food

• pigments used in photosynthesis

Evidence supporting Endosymbiotic Theory

• microscopic remains show that the older prokaryotes are 3.5b years old while eukaryotes are 1.5b

• they function similarly as they

  • both use DNA and RNA

  • same proteins and lipids

  • ATP

• eukaryotes are more structurally complex

Features of mitochondria and chloroplasts that support Endosymbiosis

• similar in size and shape to prokaryotes

• own naked circular DNA

• semi-autonomous - move and change shape

• binary fission

• 70S ribosomes and contain enzymes

• double membraned

• arise from previously existing mito and chloro

• involved in energy conversion

• antibiotics affect prokaryotes and mito and chloro the same way but not cytoplasm

Evolution of Endomembrane system and nucleus supports this theory

• internal membrane and nuclear envelope

  • evolved from infolds of plasma membrane

• endomembrane system/cell nucleus came this way too

• endoplasmic reticulum and nuclear envelope also supports this theory.