Eukaryotic cells can contain organelles that are thought to have originated from prokaryotic cells through a process called endosymbiosis. This theory suggests that certain organelles were once independent prokaryotic organisms that were engulfed by an ancestral eukaryotic cell. The main organelles that are believed to have formed through this process are:
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Mitochondria: These organelles are responsible for producing energy (ATP) through oxidative phosphorylation. They are similar in size and DNA sequence to certain bacteria, particularly alpha-proteobacteria.
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Chloroplasts: Found in plants and algae, chloroplasts are responsible for photosynthesis. They are similar to cyanobacteria, which are photosynthetic prokaryotes.
Both mitochondria and chloroplasts contain their own DNA, replicate independently of the cell cycle, and have double membranes, further supporting the endosymbiotic theory.