Endosymbiotic theory

Definition

Endosymbiotic theory explains how eukaryotic cells evolved from prokaryotic organisms through a symbiotic relationship. It proposes that certain organelles, such as mitochondria and chloroplasts, originated as free-living bacteria that were engulfed by ancestral eukaryotic cells.

5 Must Know Facts For Your Next Test

1. Mitochondria and chloroplasts have their own DNA, which is similar to bacterial DNA.
2. These organelles replicate independently of the cell they reside in, akin to how bacteria divide.
3. The double membrane structure of mitochondria and chloroplasts supports the idea they were once independent prokaryotes.
4. Phylogenetic studies show that mitochondrial DNA is closely related to proteobacteria, while chloroplast DNA is similar to cyanobacteria.
5. Antibiotics that inhibit bacterial ribosomes also affect ribosomes within mitochondria and chloroplasts.

Review Questions

• What evidence supports the endosymbiotic theory regarding mitochondria and chloroplasts?
• How does the replication process of mitochondria and chloroplasts provide clues about their evolutionary history?
• Which types of bacteria are considered ancestors of mitochondria and chloroplasts according to phylogenetic studies?

Related terms

Mitochondrion: An organelle responsible for energy production in eukaryotic cells, thought to have originated from proteobacteria.

Chloroplast: A photosynthetic organelle found in plants and algae, believed to have evolved from cyanobacteria.

Symbiosis:

A close biological interaction between two different biological organisms, often benefiting both parties involved.