Explain the hypothesis that eukaryotes evolved from prokaryotes.

The hypothesis that eukaryotic cells evolved from a symbiotic association of prokaryotes-endosymbiosis-is particularly well supported by studies of mitochondria and chloroplasts, which are thought to have evolved from bacteria living in large cells.

Explanation: Both mitochondria and chloroplasts are similar to bacteria in size, and like bacteria, they reproduce by dividing in two. Most important, both mitochondria and chloroplasts contain their own DNA, which encodes some of their components. The mitochondrial and chloroplast DNAs are replicated each time the organelle divides, and the genes they encode are transcribed within the organelle and translated on organelle ribosomes. Mitochondria and chloroplasts thus contain their own genetic systems, which are distinct from the nuclear genome of the cell. Furthermore, the ribosomes and ribosomal RNAs of these organelles are more closely related to those of bacteria than to those encoded by the nuclear genomes of eukaryotes.