Keep in mind that each protein should 'know' its correct destination in the cell. Furthermore, rough endoplasmic reticulum needs to synthesized proteins for itself, which are known as resident or constituent proteins. Many proteins will be part of the plasma membrane, and of other membranes, as transmembrane proteins. These proteins end up at different places, such as the extracellular space, plasma membrane, or at membranes and lumen of several organelles involved in the vesicular trafficking, such as Golgi apparatus, endosomes, and lysosomes. P rotein synthesis is the main function of the rough endoplasmic reticulum. Note ribosomes associated to the outer membrane of the nuclear envelope as well. Ribosomes are observed as black dots associated to endoplasmic reticulum membranes. Rough endoplasmic reticulum cisternae are observed, which extend from the nuclear envelope to the proximity of the plasma membrane. Cisternae and tubules coexist in the same cell, but those cells with an intense secretory activity show dense piles of cisternae, which means a highly developed rough endoplasmic reticulum.įiigure 2. The density of associated ribosomes influences the rough endoplasmic reticulum membranes organization, so that a high density causes a cistern-like morphology, whereas lower density is found in tubules. The name 'rough' comes from the electron microscopy images where ribosomes, black particles, are observed coating the endoplasmic reticulum membrane (Figure 2). Rough endoplasmic reticulum is organized in more or less straight tubules and flattened cisternae. The spatial distribution of the endoplasmic reticulum through the cytosol is set by the cytoskeleton, mostly microtubules in animal cells, whereas actin filaments are the major responsible for the endoplasmic reticulum distribution in plant cells. However, in some cytosolic regions there is not clear segregation between both domains, and tubules with associated ribosomes are intermingled with naked tubules. This non overlapping distribution is observed in hepatocytes, neurons and cells synthesizing steroid hormone. Rough and smooth endoplasmic reticulum do not usually share the same cytosolic space. The outer nucelar envelope membrane is continuous with the endoplasmic reticulum membranes Rough endoplasmic reticulum is organized in cisterns and tubules that show associated ribosomes, whereas smooth endoplasmic reticulum is arranged in tubules with no ribosomes attached. Rough and smooth endoplasmic reticulum membranes are continuous. Endoplasmic reticulum can be found all over the cytoplasm, from the nuclear envelope to the plasma membrane. The outer membrane of the nuclear envelope may regarded as part of the rough endoplasmic domain because it is physically continuous with the membranes of the rough endoplasmic tubules and it has many associated ribosomes doing translation.įigure 1. Smooth endoplasmic reticulum is organized in irregular and convoluted tubules, with no associated ribosomes. Rough endoplasmic reticulum membranes are arranged forming cisterns and more or less straight tubules, both having many ribosomes associated to their cysotolic membrane surface (that is why the name rough). At transmission electron microscopy, it is easy to distinguish two domains: rough and smooth endoplasmic reticulum (Figure 1). Endoplasmic reticulum membrane is thinner (around 5 nm in thickness) than other organelle membranes because they have lipids with shorter fatty acid chains.Įndoplasmic reticulum membranes are organized in domains or regions that carry out different functions. Tubules and cisterns are distributed trough the cytoplasm from the nuclear envelope to close to the plasma membrane, so that they can account for half of the total cellular membranes. Endoplasmic reticulum membrane is also continuous with the outer membrane of the nuclear envelope. Atlas of plant and animal histology.Įndoplasmic reticulum is a complex membrane-bound compartment arranged in tubules and flattened cisterns interconnected and sharing the same lumen (inner space) and membrane.

Cytosol and er lumen