Which one of the following structures is an organelle within an organelle? (a) Ribosome (b) Peroxisome (c) ER (d) Mesosome
Option A is correct. Ribosomes occur in all living cells except mammalian erythrocytes or red blood corpuscles. Depending upon the place of their occurrence, ribosomes are of two types–cytoplasmic ribosomes and organelle ribosomes. The cytoplasmic ribosomes (cytoribosomes) may remain free in the cytoplasmic matrix or attached to the cytosolic surface of endoplasmic reticulum with the help of special ribophorin or SRP protein. The organelle ribosomes are found in plastids (plastiribosomes ) and mitochondria (mitoribosomes) Cytoplasmic ribosome are of 80S type in eukaryotic cell whereas organelle ribosomes are of 70S type.
