MICROANATOMY

Detailed explanation-1: -The comparison of the measurements on nega-tively stained cytoplasmic and mitochondrial ribo-somes from Locusta (Table II) shows that the mitochondrial ribosomes are slightly smaller than the cytoplasmic ribosomes.

Detailed explanation-2: -For protein-synthesizing activity with a natural mRNA, mitochondrial ribosomes use tRNA from any cell compartment and are partly active with supernatant enzymes from cytoplasm. Cytoplasmic ribosomes are partly active with enzymes and tRNA from mitochondria or chloroplasts.

Detailed explanation-3: -Membrane-bound and free ribosomes are structurally and functionally identical. They differ only in the proteins they are making at any given time. When a ribosome happens to be making a protein with an ER signal sequence, the signal directs the ribosome to the ER membrane.

Detailed explanation-4: -The ribosomes of the chloroplasts are smaller than the cytoplasmic ribosomes. B. Chloroplasts can synthesise some of their proteins but they receive other proteins from cytoplasm.