How are polyribosomes on the endoplasmic reticulum membrane arranged so that the next initiating ribosome will find an unoccupied translocator?
Ribosomes are bound by a strand of mRNA that runs between the large and small ribosomal subunits to form polyribosome structures.
For instance, in eukaryotic cells:
-Polysomes, also known as polyribosomes, are divided into two categories in eukaryotic cells. A polysome is made up of a single mRNA and multiple ribosomes, with one ribosome for every 100 nucleotides or so. A ribosome in a eukaryotic cell takes about 30 seconds to synthesize a 400-amino-acid protein. Free polysomes are those that reside in the cytosol without a membrane, but are possibly associated with the cytoskeletal.
-The cytosolic face of the ER is closely connected with bound polysomes. Between the two types of ribosomes, no structural variations in ribosomal RNA or ribosomal proteins have been discovered. As a result, bound ribosomal subunits can be contained in the free population, and vice versa.