RibosomesRibosomes are the most numerous organelles. An individual cell may contain up to millions of ribosomes. Some ribosomes are found floating in the cytoplasm, while others are found attached to the rough ER. Each ribosome is made from a large and a small subunit, these subunits consist of ribosomal RNA and proteins. Subunits are produced in the nucleolus; then they are sent out into the cytoplasm, where they join together after attaching to messenger RNA.
The ribosomes' job is to produce proteins as instructed by messenger RNA. Ribosomes suspended in the cytoplasm often cluster together (called polysomes), they produce proteins that will be used within the cell. On the other hand, ribosomes attached to the rough ER makes proteins for export or for the cell membrane. In order to synthesize proteins, ribosomes read the genetic code from messenger RNA and translate it into the primary structure of a protein. Due to their ability to synthesize proteins, ribosomes are especially important for cells that need to produce a lot of proteins or growing cells. |