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 contain 70S ribosomes, which are similar to those found in prokaryotic cells, such as bacteria. This is an important feature because it supports the theory of endosymbiosis, which suggests that mitochondria are the evolutionary descendants of ancient bacteria that were engulfed by a primitive eukaryotic cell.

Details about 70S ribosomes:

• 70S ribosomes: These ribosomes are smaller than the 80S ribosomes found in the cytoplasm of eukaryotic cells. They consist of a 50S large subunit and a 30S small subunit. The "S" (Svedberg unit) refers to the sedimentation rate, which is a measure of how quickly particles move in a centrifuge.
• Prokaryotic ribosomes: The 70S ribosomes are characteristic of prokaryotic organisms like bacteria. This feature is shared by mitochondria, which, like bacteria, are believed to have evolved from a prokaryotic ancestor.
• Endosymbiotic theory: According to this theory, mitochondria were once free-living bacteria that were engulfed by a host cell in a symbiotic relationship. Over time, the engulfed bacteria became mitochondria, but they retained some of their original characteristics, including the 70S ribosomes.

Why do mitochondria have 70S ribosomes?

Mitochondria replicate independently from the host cell and contain their own DNA, which codes for some of their proteins. To produce these proteins, mitochondria use their 70S ribosomes to translate the mitochondrial DNA. This process is similar to how bacterial ribosomes function, further supporting the idea that mitochondria evolved from prokaryotic ancestors.

In contrast, other organelles in eukaryotic cells, such as the endoplasmic reticulum and the Golgi apparatus, contain 80S ribosomes, which are larger and structurally different from the 70S ribosomes found in mitochondria.