Endosimbiosis (teoría endosimbiótica)

The Theory of Endosymbiosis

Introduction to Endosymbiosis

• Endosymbiosis is defined as a symbiotic relationship where one cell resides within another.

• The endosymbiotic theory explains the evolution from prokaryotic cells to eukaryotic cells, transitioning through anaerobic and aerobic stages.

Historical Development of the Theory

• Initial ideas about endosymbiosis were proposed by Constantine Merezhkovsky in the early 20th century.

• Lynn Margulis developed the modern endosymbiotic theory, publishing her findings in 1967.

Evolution of Eukaryotic Cells

• The first eukaryotic cell was anaerobic and emerged approximately 2.7 billion years ago from a fusion between an archaeon that utilized sulfur and heat for energy and a bacterium.

• This primitive eukaryotic cell captured aerobic bacteria, establishing a mutualistic relationship where bacteria provided energy in exchange for shelter and nutrients.

Development of Mitochondria

• Over time, captured aerobic bacteria evolved into mitochondria, enabling the success of new eukaryotic cells in oxygen-rich environments.

• Animals and fungi are considered products of this evolutionary process involving mitochondria.

Emergence of Photosynthetic Eukaryotes

• Approximately 1.2 billion years ago, another eukaryotic cell captured photosynthetic bacteria, leading to another symbiotic relationship.

• These photosynthetic bacteria eventually evolved into chloroplasts, which perform photosynthesis; this fusion gave rise to ancient green algae, ancestors of current plant cells.

Evidence Supporting Endosymbiosis

• Mitochondria and chloroplasts share several characteristics with prokaryotes:

• They contain circular DNA similar to prokaryotes while eukaryotic nuclei have linear chromosomes.

• Both organelles are surrounded by double membranes consistent with phagocytosis theories.