Which cellular feature supports the bacterial origin of mitochondria and chloroplasts?

Which cellular feature supports the bacterial origin of mitochondria and chloroplasts?

• A. Linear DNA with histones
• B. Ribosomes are not present
• C. Circular DNA and prokaryote-like ribosomes
• D. Enclosed by a single membrane

Answer: (C)

The main idea is that evidence for the bacterial origin of mitochondria and chloroplasts comes from their bacterial-like genetic and molecular traits. These organelles carry circular DNA, not linear DNA wrapped around histones as in the eukaryotic nucleus, and they use prokaryote-like ribosomes (70S) to synthesize proteins inside the organelle. That combination—circular genomes and 70S ribosomes—fits what we know about bacteria and supports the idea that these organelles originated from free-living bacteria that were taken up by ancestral cells. The other descriptions don’t fit this story: linear DNA with histones is a eukaryotic feature, ribosomes are present in these organelles, and they are typically enclosed by two membranes rather than a single membrane, all of which align more with an endosymbiotic origin rather than the bacterial pattern.

The main idea is that evidence for the bacterial origin of mitochondria and chloroplasts comes from their bacterial-like genetic and molecular traits. These organelles carry circular DNA, not linear DNA wrapped around histones as in the eukaryotic nucleus, and they use prokaryote-like ribosomes (70S) to synthesize proteins inside the organelle. That combination—circular genomes and 70S ribosomes—fits what we know about bacteria and supports the idea that these organelles originated from free-living bacteria that were taken up by ancestral cells. The other descriptions don’t fit this story: linear DNA with histones is a eukaryotic feature, ribosomes are present in these organelles, and they are typically enclosed by two membranes rather than a single membrane, all of which align more with an endosymbiotic origin rather than the bacterial pattern.