The outer membrane of the endoplasmic reticulum
contain small granules commonly known as ribosomes, which are the smallest
particulate components of the cytoplasm. They are rich in ribonucleic acids.
Each ribosome has a large and a small subunit with a sedimentation constant of
50s and 30s respectively (Fig. 1.8). Each subunit contains about 65% RNA and
are the sites of protein synthesis. Messenger RNA binds in the groove between
the subunits and specifies the sequence of amino acids in the growing
polypeptide chains. The proteins synthesized on membrane bound ribosomes must
pass successively through each of cytomembrane system.
may involve the fusion of the vacuoles with the plasma membrane followed by a
discharge of the contents into the extra cellular space. This process is called