Smooth+and+Rough+Endoplasmic+Reticulum

__Endoplasmic Reticulum__

The endoplasmic reticulum (**ER**) is a network of flattened sacs and branching tubules that extends throughout the cytoplasm in plant and animal cells. These sacs and tubules are all interconnected by a single continuous membrane so that the organelle has only one large, highly convoluted and complexly arranged **lumen** (internal space). Usually referred to as the endoplasmic reticulum cisternal space, the lumen of the organelle often takes up more than 10 percent of the total volume of a cell. The endoplasmic reticulum membrane allows molecules to be selectively transferred between the lumen and the cytoplasm, and since it is connected to the double-layered nuclear envelope, it further provides a pipeline between the nucleus and the cytoplasm. The endoplasmic reticulum manufactures, processes, and transports a wide variety of biochemical compounds for use inside and outside of the cell. Consequently, many of the proteins found in the cisternal space of the endoplasmic reticulum lumen are there only transiently as they pass on their way to other locations. Other proteins, however, are targeted to constantly remain in the lumen and are known as endoplasmic reticulum **resident proteins**. These special proteins, which are necessary for the endoplasmic reticulum to carry out its normal functions, contain a specialized retention signal consisting of a specific sequence of amino acids that enables them to be retained by the organelle. An example of an important endoplasmic reticulum resident protein is the chaperone protein known as **BiP** (formally: the chaperone immunoglobulin-binding protein), which identifies other proteins that have been improperly built or processed and keeps them from being sent to their final destinations.

Davidson, Michael W. "Endoplasmic Reticulum." __Molecular Expressions Cell Biology__. 1 Oct. 2000. Florida State University. 13 Dec. 2004 .

Video of Cell Orgenelles: Starring the Infamous Endoplasmic Reticulum

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Smooth Endoplasmic Reticulum__

This electron micrograph shows an area of smooth endoplasmic reticulum consisting of tortuous tubules and vesicles. This field is from a liver cell. The smooth endoplasmic reticulum serves to metabolize glycogen (which are deposited as black rosettes over the area), and it contains enzymes needed to detoxify drugs. In adrenal cortical cells (as well as steroid producing cells in the gonads), the smooth endoplasmic reticulum serves to metabolize the steroids and produced the final steroid hormone. After the side chain of cholesterol is cleaved in the mitochondria, the product is passed to the smooth endoplasmic reticulum and further modified. Then, it is passed back to mitochondria for final modifications. Thus, the two organelles play a sort of "steroid volleyball" to produce the steroid hormone. || Childs, Gwen V. "Smooth Endoplasmic Reticulum." __Smooth Endoplasmic Reticulum__. 27 Aug. 2001. University of Texas Medical Branch. 27 Oct. 2008 .
 * Smooth endoplasmic reticulum is found in a variety of cell types and it serves different functions in each. It consists of tubules and vesicles that branch forming a network. In some cells there are dilated areas like the sacs of rough endoplasmic reticulum. The network of smooth endoplasmic reticulum allows increased surface area for the action or storage of key enzymes and the products of these enzymes. In the case of smooth endoplasmic reticulum in muscle cells, the vesicles and tubules serve as a store of calcium which is released as one step in the contraction process. Calcium pumps serve to move the calcium.

__Rough Endoplasmic Reticulum__

Rough endoplasmic reticulum bears the ribosomes during protein synthesis. The newly synthesized proteins are sequestered in sacs, called. The system then sends the proteins via small vesicles to the[| Golgi Complex], or, in the case of [|membrane proteins], it inserts them into the membrane. As shown in this diagram, rough endoplasmic reticulum may either be vesicular or tubular. Or it may consist of stacks of flattened cisternae (like sheets) that may have bridging areas connecting the individual sheets. The sit on the outer surfaces of the sacs (or cisternae). They resemble small beads sitting in rosettes or in a linear pattern.
 * [[image:http://cellbio.utmb.edu/cellbio/rer14.jpg width="350" height="138" align="left" link="http://cellbio.utmb.edu/cellbio/cit1.htm"]]Rough endoplasmic reticulum forms a reticulum that expands as the cell becomes more active in protein synthesis. Sometimes the reticulum branches out. Other times, the cisternae dilate and form large sacs that fill the cell. This photograph, taken from your text, shows the reticulum delineated by immunolabeling for newly synthesized protein (labeled fluorescent blue in this photo). ||

Childs, Gwen V. "Endoplasmic Reticulum." __Endoplasmic Reticulum__. 27 Aug. 2001. University of Texas Medical Branch. 27 Oct. 2008 .



Cell Theory Rap

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Links:

[|Encyclopedia Britannica: ER]

[|Interactive Cell]

[|Endoplasmic Reticulum]