Eukaryotic cells are distinguished by membrane-bound organelles such as mitochondria and chloroplasts. Two hypotheses propose different models for how these organelles originated.
*Hypothesis 1 (Endosymbiotic Hypothesis)*
Organelles evolved when a large, ancestral anaerobic prokaryote engulfed smaller, specialized prokaryotes. Specifically, aerobic bacteria were engulfed and became mitochondria, while photosynthetic bacteria (cyanobacteria) were engulfed and became chloroplasts. Over time, these engulfed cells formed a symbiotic relationship with the host cell. A key belief of this hypothesis is that organelles contain their own distinct genetic material, which behaves independently of the host's nuclear genome and resembles bacterial DNA.
*Hypothesis 2 (Autogenous Hypothesis)*
Organelles evolved intracellularly through the progressive invagination (infolding) and specialization of the ancestral prokaryotic cell's own plasma membrane. The membrane folds pinched off to form internal compartments that gradually specialized into organelles like mitochondria and chloroplasts. According to this model, the DNA within these organelles is a subset of the cell’s ancestral nuclear DNA, and organelle replication is fully integrated with and controlled by the cell's main nuclear genome.
Based on Hypothesis 2, which of the following statements best describes the origin of the genetic material found within a eukaryotic cell's mitochondria?
- It evolved from the nuclear genome of the ancestral prokaryotic cell as its membrane invaginated.Answer
- BIt was acquired from an engulfed aerobic prokaryotic cell that established a symbiotic relationship.
- CIt was derived from photosynthetic cyanobacteria that were captured by the host cell.
- DIt was synthesized entirely from cytoplasmic protein complexes without ancestral DNA templates.