"Mitochondria and chloroplasts have their own DNA, which is circular and resembles that of bacteria."
Here's why this statement is so compelling:
* Circular DNA: Bacteria have circular DNA, unlike the linear chromosomes found in the nucleus of eukaryotic cells. The fact that mitochondria and chloroplasts possess their own circular DNA strongly suggests they were once independent bacteria.
* Similar Size and Structure: Mitochondria and chloroplasts are roughly the same size as bacteria, and they have their own ribosomes, which are also similar in size and structure to bacterial ribosomes.
* Double Membranes: Both mitochondria and chloroplasts have double membranes, which could have arisen from the engulfing of a prokaryotic cell by a larger cell.
Other supporting evidence:
* Replication: Mitochondria and chloroplasts replicate independently of the eukaryotic cell, similar to how bacteria reproduce.
* Protein Synthesis: They have their own protein synthesis machinery, which is more similar to bacteria than to the eukaryotic cell.
The theory of endosymbiosis proposes that mitochondria and chloroplasts originated from free-living prokaryotes that were engulfed by larger cells. Over time, these engulfed prokaryotes evolved into the organelles we see today. The presence of their own DNA and other bacterial-like features provides strong evidence for this theory.
