The Rough endoplasmic reticulum got its name from the appearance of Ribosomes on the membrane of the rough ER when observed with a light microscope. In most places the membranes forming the Endoplasmic reticulum are studded with minute particles of RNA called ribosomes. The presence of these ribosomes gives the membrane a rough appearance hence the name Rough Endoplasmic Reticulum or Granular Endoplasmic Reticulum.
Rough Endoplasmic Reticulum Structure
The rough endoplasmic reticulum has rough, bumpy or bead-like appearance and usually vesicular or tubular in structure. This rough appearance is due to the attachment of granular ribosomes to its outer surface hence, it is also called the granular endoplasmic reticulum. Attached to the outer surfaces of many parts of the endoplasmic reticulum are large numbers of minute granular particles called Ribosomes. Where these are present, the reticulum is called the granular endoplasmic reticulum. The ribosomes are composed of a mixture of RNA and proteins, and they function to synthesize new protein molecules in the cell. The lumen of rough endoplasmic reticulum is continuous with the perinuclear space (between the inner and outer membranes of the Nucleus) and also continuous with the lumen of smooth endoplasmic reticulum.
Rough Endoplasmic Reticulum Function
- Rough Endoplasmic reticulum represents the site at which proteins are synthesized.
- The granular endoplasmic reticulum (rough ER) is also concerned with the initial folding of polypeptide chains with the formation of disulfide bonds
Function of the Rough Endoplasmic Reticulum in the synthesis of proteins
Rough endoplasmic reticulum is concerned with the synthesis of proteins in the cell. It is involved with the synthesis of mainly those proteins which are secreted from the cells such as insulin from cells of islets of Langerhans in pancreas and antibodies from B-lymphocytes.
Ribosomes arrange the amino acids into small units of proteins and transport them into the rough endoplasmic reticulum. Here, the carbohydrates are added to the protein units forming the glycosylated proteins or glycoproteins, which are arranged in the form of reticular vesicles. These vesicles are transported mainly to Golgi apparatus for further modification and processing. Few vesicles are transported to other organelles in the Cytoplasm.
Function of the Rough Endoplasmic Reticulum in the Degradation of worn-out organelles
Rough endoplasmic reticulum also plays an important role in the degradation of worn-out cytoplasmic organelles like mitochondria. It wraps itself around the worn-out organelles and forms a vacuole which is often called the Autophagosome. Autophagosome is digested by lysosomal enzymes.