What are the differences between ribosomes and endoplasmic reticulum?

Endoplasmic reticulum and ribosomes are two types of organelles that work together to synthesize proteins and transport them to their various destinations. There are several differences between these two organelles. 

Endoplasmic reticulum 

Endoplasmic reticulum is a membrane-bound organelle. It is made up of tubes and sacs, called cisternae, enclosed in a complex network of membranes inside a cell. The endoplasmic reticulum extends from the exterior surface of the nuclear membrane into the body of the cell. It is continuous with the nuclear membrane and plays a key role in protein synthesis, lipid metabolism, and calcium storage. 

There are two types of endoplasmic reticulum – smooth and rough. The rough endoplasmic reticulum (rough ER) acts as a host for ribosomes that continuously attach to and detach from its outer surface. The main function of the rough ER is to facilitate the synthesis and storage of proteins. Many of the proteins synthesized by the attached ribosomes pass into the rough endoplasmic reticulum, from where they are transported to other parts of the cell for immediate use or to be stored or transported out of the cell to other parts of the organism.

Ribosomes

Ribosomes are small, round, membrane-less organelles. They are composed of ribosomal RNA and proteins and make up of a large and a small subunit. Ribosomes may be found floating freely in the cell cytosol or attached to the outer surface of the rough endoplasmic reticulum through tiny, complex docking stations called translocons.  

Ribosomes are the main site of protein synthesis. They synthesize proteins through a process called translation, which occurs in three distinct phases. The newly synthesized protein is transported through the translocon into the endoplasmic reticulum. From there it may be transported to other parts of the cell to be used immediately or it may be transported out the cell to other parts of the organism. Proteins that are not needed for immediate use are stored in the rough ER.