Rough endoplasmic reticulum
The endoplasmic reticulum (ER) is an organelle made up of a network of flattened sacs or tubules. The membranes of the ER are connected to the nuclear membrane and run through the cytoplasm. There are two types of ER: (1) the rough endoplasmic reticulum (rER) and (2) the smooth endoplasmic reticulum (sER).
The rER is bears many ribosomes on its outer surface giving it a rough appearance as seen under the microscope; hence, the name. The presence of ribosomes on rER is an indication that the latter is involved in protein synthesis and secretion. The organelle synthesizes and secretes serum proteins (such as albumin) in the liver, and hormones (such as insulin) and other substances (such as milk) in the glands. Nevertheless, the ribosomes that give the endoplasmic reticulum a 'rough' appearance are not always bound to the ER. They bind to it when it starts to synthesize membrane-bound proteins destined for sorting. A cue is a particular protein-nucleic acid complex that forms in the cytosol.
Abbreviation / Acronym: rER