Endosymbiotic theory

Definition

Endosymbiotic theory proposes that certain organelles, such as mitochondria and chloroplasts, originated as free-living prokaryotes that were engulfed by ancestral eukaryotic cells. This relationship allowed these prokaryotes to become integral parts of the eukaryotic cell, leading to the complex cell structures we see today. The theory connects to the evolution of eukaryotes, emphasizing the importance of symbiotic relationships in the development of life forms with specialized functions.

5 Must Know Facts For Your Next Test

1. The endosymbiotic theory was popularized by Lynn Margulis in the 1960s, providing a new understanding of how complex cells evolved.
2. Mitochondria and chloroplasts have their own DNA, which is similar to bacterial DNA, supporting the idea that they originated from prokaryotic ancestors.
3. The double membrane structure of mitochondria and chloroplasts is consistent with the process of being engulfed by larger cells.
4. Endosymbiosis is not limited to mitochondria and chloroplasts; it may also explain the origin of other organelles and even some cellular processes.
5. The acceptance of the endosymbiotic theory has led to a deeper understanding of evolutionary biology, highlighting the significance of cooperation and symbiosis in evolution.

Review Questions

• How does the endosymbiotic theory explain the presence of mitochondria and chloroplasts in eukaryotic cells?
  • The endosymbiotic theory suggests that mitochondria and chloroplasts were once independent prokaryotic organisms that entered into a symbiotic relationship with ancestral eukaryotic cells. By being engulfed by these early eukaryotes, these prokaryotes provided essential functions such as energy production and photosynthesis. Over time, they became integral components of the eukaryotic cell, leading to more complex cellular structures.
• Discuss how molecular evidence supports the endosymbiotic theory in relation to organelle evolution.
  • Molecular evidence supporting the endosymbiotic theory includes similarities in DNA sequences between mitochondrial and chloroplast genomes and those of certain prokaryotes. Additionally, both organelles possess their own circular DNA, similar to bacterial chromosomes, and replicate independently of the host cell's nucleus. This genetic evidence strengthens the argument that mitochondria and chloroplasts originated from ancestral prokaryotic cells that formed a symbiotic relationship with early eukaryotic organisms.
• Evaluate the broader implications of the endosymbiotic theory for our understanding of evolutionary processes in living organisms.
  • The endosymbiotic theory has significant implications for our understanding of evolution, emphasizing that complex life forms can emerge not only through genetic mutations but also through symbiotic relationships. This highlights how cooperation among different organisms can lead to new functions and adaptations. It also encourages a re-evaluation of how we perceive evolutionary processes, suggesting that collaboration between species plays a vital role in shaping biodiversity and the development of life on Earth.

Related terms

Eukaryote: An organism whose cells contain a nucleus and other membrane-bound organelles, distinguishing them from prokaryotes.

Mitochondria:

Organelles found in eukaryotic cells that are responsible for energy production through cellular respiration, believed to have originated from engulfed prokaryotes.

Chloroplasts:

Organelles in plant cells that carry out photosynthesis, thought to have originated from photosynthetic bacteria through endosymbiosis.