TYPES OF RIBOSOMES

Ribosomes;

The ribosomes occur in cells, both Prokaryotic and eukaryotic cells. In Prokaryotic cells the ribosomes often occur freely in the cytoplasm.
In eukaryotic cells the ribosomes either occur freely in the cytoplasm or remain attached to the outer surface of membrane of endoplasmic reticulum.

TYPES OF RIBOSOMES ;
        Recently accuroding to the size and the sedimentation coefficient (S) two types of ribosomes have been recognised.

70S Ribosomes;
             The 70S ribosomes are comparatively smaller in size and have sedimentation coefficient 70S and the molecular weight 2.7×106 daltons.
One dalton equals the weight of hydrogen atom.
According to the data of electron microscopy the dimension of the dry particles of 70S ribosomes are 170×170×200 A°.
They occur in the Prokaryotic cells of the blue green algae and bacteria and also in mitochondria and chloroplasts of eukaryotic cells.

80S Ribosomes;
              The 80S ribosomes some have the sedimentation coefficient of 80S and the molecular weight 40 × 10×10×10×10×10×10 daltons.
The 80S ribosomes occur in eukaryotic cells of the plants and animals.
The ribosomes of mitochondria and chloroplasts are always smaller than 80S cytoplasmic ribosomes and are comparable to Prokaryotic ribosomes in both size and sensitivity to antibiotics, although their sedimentation values vary in different phyla, e.g., 77S in mitochondria of Fungi , 60S in mitochondria of mammals and 60S in mitochondria of animals in general.
The ribosomes of chloroplasts are 70S type.