Saturday, December 7, 2013

Ribosomes: Protein Factories

Ribosomes are nonmembranous organelles responsible for the synthesis of proteins from amino acids. They are composed of RNA and protein. Each ribosome is composed of two subunits—a large one and a small one. As mentioned before, they are constructed in the Nucleolus. Ribosomes carry out protein synthesis in two locations

Bound ribosomes: Many ribosomes are attached to the endoplasmic reticulum. Because ER that has attached ribosomes appears rough when viewed through an electron microscope it is called rough ER. Areas of rough ER are active sites of protein production.

Free ribosomes: Many ribosomes are also found floating freely in the cytoplasm wherever proteins are being assembled. Cells that are actively producing protein (e.g., liver cells) have great numbers of free and attached ribosomes. Ribosomes are not surrounded by membrane (found in prokaryotic cells too)