Question

Which of the following organisms or organelles contain 70S ribosomes?

• A. Animal cell cytoplasm
• B. Mitochondria
• C. Plant cell cytoplasm
• D. Nucleus

Hint:

Mitochondria are similar to prokaryotic cells in many aspects, including the presence of 70S ribosomes.

Answer 1

The Correct Option is B

The correct answer is mitochondria.

Mitochondria possess 70S ribosomes, analogous to those in prokaryotic cells like bacteria. This similarity supports the endosymbiotic theory, postulating that mitochondria originated from ancient bacteria engulfed by a primitive eukaryotic cell.

Details about 70S ribosomes:

• 70S ribosomes: These are smaller than the 80S ribosomes found in eukaryotic cytoplasm. They comprise a 50S large subunit and a 30S small subunit. The "S" (Svedberg unit) denotes sedimentation rate in centrifugation.
• Prokaryotic ribosomes: 70S ribosomes are characteristic of prokaryotes, such as bacteria. Mitochondria share this trait, suggesting an evolutionary link to prokaryotic ancestors.
• Endosymbiotic theory: This theory posits that mitochondria were once free-living bacteria endosymbiosed by a host cell. They evolved into mitochondria but retained prokaryotic features, including 70S ribosomes.

Reason for 70S ribosomes in mitochondria:

Mitochondria replicate autonomously and contain their own DNA encoding some proteins. They utilize their 70S ribosomes to translate this DNA, mirroring bacterial ribosome function and reinforcing their prokaryotic origin.

Conversely, other eukaryotic organelles, such as the endoplasmic reticulum and Golgi apparatus, utilize 80S ribosomes, which are larger and structurally distinct from mitochondrial 70S ribosomes.