What are Ribosomes?
Ribosomes are the cell organelles which serve as the site for protein synthesis (Translation). These are made up of special proteins and nucleic acids. Ribosomes are found in all living cells. In prokaryotic cells, they float freely in the cytoplasm. Whereas in the eukaryotes they can be found at many places, you can find them freely floating in the cytosol, attached to the endoplasmic reticulum or attached to the nuclear membrane. There are two types of ribosomes; Free Ribosomes and Bound Ribosomes.
Difference between Free Ribosomes and Bound Ribosomes
The location of the ribosomes is the main difference between free and bound ribosomes. Free ribosomes are located in the cytoplasm freely floating. They are not attached to any other structure in the cell. But they can be attached with other ribosomes to form polysomes. They can move all around the cell. Bound ribosomes are attached to the surface of the endoplasmic reticulum. The endoplasmic reticulum to which ribosomes are attached is called rough endoplasmic reticulum. Some ribosomes are also attached to the nuclear membrane. These ribosomes cannot move to the other parts of the cell.
The types of proteins synthesized by the ribosomes is another difference between free and bound ribosomes. Ribosomes which float in the cytosol make proteins which are used in the cell. Those which are attached to ER make proteins which are either used inside the cell or are transported outside the cell. Ribosomes attached to nuclear envelope synthesize proteins for release in the perinuclear space.
Functions of Ribosomes
Both free and Bound ribosomes translate the encoded information provided by mRNA in the cell nucleus, then they link the amino acids which are selected and collected by the tRNA from the cytoplasm (however, the order of linking up of amino acids is determined by mRNA). They, then export the polypeptide formed in this process, to the cytoplasm where it will be used to form a functional protein. The proteins synthesized by free ribosomes are sent to the Golgi apparatus for packaging. While the proteins synthesized by bound ribosomes remain in the endoplasmic reticulum. At the end proteins synthesized by both types of ribosomes are modified and transported to their final destinations.