Question

70S ribosome is present in
(a)Chloroplast
(b)Mitochondria
(c)Prokaryotic
(d)All of the above

Answer 1

Hint: Ribosomes are macromolecular cell organelles that perform biological protein synthesis. They are the smallest known organelles. They can be of 70S, 80S, 55S, etc types where ‘S’ is the sedimentation coefficient.

Complete step-by-step answer:
Ribosomes are found in the cytoplasm of the cells. While they are found only in free form in the cytoplasm of prokaryotes, they are also found bound to the endoplasmic reticulum and outer nuclear membrane in the eukaryotes.
They are also found inside some cell organelles like chloroplasts and mitochondria.
In eukaryotic cells the ribosomes present are of 80S type, whereas in prokaryotic cells and in chloroplasts and mitochondria they are of 70S type.

Additional Information:
-Each ribosome is formed of two unequally sized subunits, which join temporarily at the time of protein synthesis.
-In 70S ribosomes the larger subunit is 50S and the smaller subunit is 30S; while in the 80S ribosomes, the larger subunit is 60S and the smaller subunit is 40S.
-The cohesion of subunits depends on the molar concentration of magnesium (0.001M) ions. If the concentration decreases the subunits detach. Conversely if the concentration increases beyond 0.001M to ten folds, two ribosomes unite to form dimers.
-Chloroplasts and Mitochondria are believed to have been developed from prokaryotic cells.
-A supportive factor for this theory is the presence of 70S ribosomes in these cell organelles.
So, the correct answer is ‘All of the above’

Note: Endosymbiotic hypothesis: It is the hypothesis behind the origin of mitochondria and chloroplast, which states that they were originally specialized non-sulphur bacteria that survived endocytosis.
-They developed a commensal relationship with the host cell and became incorporated into the cells.