Overview
This lecture discusses the endosymbiotic theory, which explains the origin of eukaryotic cells through symbiosis between different prokaryotic species.
Symbiosis and Endosymbiosis
- Symbiosis is a persistent, mutually beneficial relationship between organisms of different species, like bees and plants.
- Endosymbiosis refers to one cell living inside another, forming a stable association.
Endosymbiotic Theory and Eukaryotic Cells
- Lynn Margulis popularized the endosymbiotic theory in 1967.
- The theory states that eukaryotic cells originated from prokaryotic cells entering into symbiotic relationships.
- According to the hypothesis, certain prokaryotes engulfed others, leading to evolutionary leaps and the rise of eukaryotic cells.
- Eukaryotic cells are the result of accumulated mutations and integration of pre-existing prokaryotic structures.
- This process enabled new functions, such as photosynthesis and oxidative metabolism, altering Earth's primitive atmosphere.
Evidence for Endosymbiosis
- Mitochondria and chloroplasts have similar sizes and shapes to certain bacteria.
- Both organelles contain their own DNA, RNA, and ribosomes, allowing self-replication independent of the cell nucleus.
- Their DNA is circular, like bacterial DNA.
Key Terms & Definitions
- Symbiosis — a close, long-term relationship between organisms of different species.
- Endosymbiosis — a form of symbiosis where one organism lives inside another.
- Prokaryote — a cell lacking a nucleus, such as bacteria.
- Eukaryote — a cell with a nucleus, evolved through endosymbiosis.
- Mitochondria — organelles responsible for oxidative metabolism in cells.
- Chloroplasts — organelles enabling photosynthesis in plant cells.
Action Items / Next Steps
- Review the main features of mitochondria and chloroplasts.
- Prepare for discussion on the impact of endosymbiosis on cell evolution.