external image rer14.jpgRough 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).



.:Endoplasmic Reticulubum:.

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Endoplasmic Reticulum and Nuclear Envelope
Endoplasmic Reticulum and Nuclear Envelope


Endoplasmic Reticulum - The endoplasmic reticulum is a network of sacs that manufactures, processes, and transports chemical compounds for use inside and outside of the cell. It is connected to the double-layered nuclear envelope, providing a pipeline between the nucleus and the cytoplasm.




external image rer1.jpgEndoplasmic reticulum is a network of tubules, vesicles and sacs that are interconnected. They may serve specialized functions in the cell including protein synthesis, sequestration of calcium, production of steroids, storage and production of glycogen, and insertion of membrane proteins. The first part of this presentation will focus on rough endoplasmic reticulum which gets its name from the presence of ribosomes on its surface.

The 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.

Animal Cell Endoplasmic Reticulum
Animal Cell Endoplasmic Reticulum


An organelle in the cell is the endoplasmic reticulum (ER). While the function of the nucleus is to act as the cell brain, the ER functions as a packaging system. It does not work alone. The ER works closely with the Golgi apparatus, ribososmes, RNA, mRNA, and tRNA. It creates a network of membranes found through the whole cell. The ER may also look different from cell to cell, depending on the cell's function. Endoplasmic reticulum is a network of tubules, vesicles and sacs that are interconnected. They may serve specialized functions in the cell including protein synthesis, sequestration of calcium, production of steroids, storage and production of glycogen, and insertion of membrane proteins. The first part of this presentation will focus on rough endoplasmic reticulum which gets its name from the presence of ribosomes on its surface.

Rough Endoplasmic Reticulum
Rough Endoplasmic Reticulum

Rough and Smooth

There are rough ER and smooth ER. They both have the same types of membranes but they have different shapes and rough ER has ribosomes attached. Rough ER looks like sheets of bumpy membranes while smooth ER looks more like tubes. Sometimes the ER looks like a flat balloon. Sacs of the ER called cisternae store the complex molecules.

Smooth Endoplasmic Reticulum
Smooth Endoplasmic Reticulum
Smooth ER has its purpose in the cell. It acts as a storage organelle. It is important in the creation and storage of steroids. It also stores ions in solution that the cell may need at a later time. Steroids are a type of ringed organic molecule used for many purposes in an organism. They are not always about building muscle mass like a weight lifter. The ion storage is important because sometimes a cell needs ions fast. It might not want to search the environment for ions, so it is easier to have them stored in a pack for easy use.

Rough ER was mentioned in the section on ribosomes. They are very important in the synthesis and packaging of proteins. Some of those proteins might be used in the cell and some are sent out. The ribosomes are attached to the membrane of the ER. As the ribosome builds the amino acid chain, the chain is pushed into the ER. When the protein is complete, the rough ER pinches off a vesicle. That vesicle, a small membrane bubble, can move to the cell membrane or the Golgi apparatus.
A fluorescently stained image of the endoplasmic reticulum (green).

Endoplasmic Reticulum
Endoplasmic Reticulum

The second type of ER, is smooth ER (SER). SER is abundant in cells that are involved in lipid metabolism. Cells that synthesize steroid hormones from cholesterol have an expanded SER to accommodate enzymes that make cholesterol and convert it into hormones.
Once a protein synthesized on a membrane-bound ribosome, it passes across the membrane of ER where the protein is processed by enzymes and folded into its correct three-dimensional conformation. Following the ER, the protein enters the Golgi apparatus where it is further modified by the addition of polysaccharide chains and packaged into vesicles. The ultimate fate of the protein is to be secreted out of the cell via exocytosis of the vesicles. All cells were processed using a gluteraldehyde fixation with an ER specific dye, 3,3'-dihexyloxacarbocyanine iodide (DiOC6(3)).


Endoplasmic Reticulum Page 2
Endoplasmic Reticulum Page 2
Endoplasmic Reticulum Page 3
Endoplasmic Reticulum Page 3


Process of protein synthesis
Process of protein synthesis
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There are two types of Endoplasmic Reticulum: Rough and Smooth-
-Smooth ER
has its purpose in the cell. It acts as a storage organelle. It is important in the creation and storage of steroids. It also stores ions in solution that the cell may need at a later time. Steroids are a type of ringed organic molecule used for many purposes in an organism. They are not always about building muscle mass like a weight lifter. The ion storage is important because sometimes a cell needs ions fast. It might not want to search the environment for ions, so it is easier to have them stored in a pack for easy use.
The Smooth ER differs from the RER in lacking attached ribosomes and usually being tubular rather than disc-like.
A major function of the SER is the synthesis of lipids
  • from which various cell membranes are made or which,
  • like steroids, are secreted from the cell.
  • the cells of the adrenal cortex (which secrete steroid hormones);
  • the cells of the liver (hepatocytes) where it synthesis lipids for secretion of lipoproteins.
  • The sarcoplasmic reticulum of muscle cells is SER.

    -Rough ER was mentioned in the section on ribosomes. They are very important in the synthesis and packaging of proteins. Some of those proteins might be used in the cell and some are sent out. The ribosomes are attached to the membrane of the ER. As the ribosome builds the amino acid chain, the chain is pushed into the ER. When the protein is complete, the rough ER pinches off a vesicle. That vesicle, a small membrane bubble, can move to the cell membrane or the Golgi apparatus.
The Rough ER is typically arranged as interconnecting stacks of disc-like sacs. The cytosolic surface of the RER is studded with ribosomes engaged in protein synthesis.
As the messenger RNA is translated by the ribsome, the growing polypeptide chain is inserted into the membrane of the RER.
  • Proteins destined to be secreted by the cell or shipped into the lumen of certain other organelles like the Golgi apparatus and lysosomes pass all the way through into the lumen of the RER.
  • Transmembrane proteins destined for the plasma membrane or the membrane of those organelles are retained within the membrane of the RER.
  • cells secreting digestive enzymes (e.g. the pancreas cell above);
  • antibody-secreting plasma cells.




The endoplasmic reticulum (ER) is a eukaryotic organelle that forms an interconnected network of tubules, vesicles, and cisternae within cells. The lacey membranes of the endoplasmic reticulum were first seen by Keith R. Porter, Albert Claude, and Ernest F. Fullam in 1945.[1[[http://en.wikipedia.org/wiki/Endoplasmic_reticulum#cite_note-FirstER-0|]]]
These structures are responsible for several specialized functions: protein translation, folding and transport of proteins to be used in the cell membrane (e.g. transmembrane receptors and other integral membrane proteins), or to be secreted (exocytosed) from the cell (e.g. digestive enzymes); sequestration of calcium; and production and storage of glycogen, steroids, and other macromolecules.[2[[http://en.wikipedia.org/wiki/Endoplasmic_reticulum#cite_note-1|]]] The endoplasmic reticulum is part of the endomembrane system. The basic structure and composition of the ER membrane is similar to the plasma membrane.

external image 315px-Clara_cell_lung_-_TEM.jpg Micrograph of rough endoplasmic reticulum network around the nucleus (shown in lower right-hand side of the picture). Dark small circles in the network are mitochondria.

The Endoplasmic Reticulum are maze passageways in the cytoplasm. They carry proteins from one part of the cell to another. This is very important for the cell to get its protein that it needs. This is like a conveyor belt.
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Endoplasmic Reticulum: Protein Clothier and Lipid Factory

If you peer over the side of the nucleus, you'll notice groups of enormous, interconnected sacs snuggling close by. Each sac is only a few inches across but can extend to lengths of 100 feet or more. This network of sacs, the endoplasmic reticulum (ER), often makes up more than 10 percent of a cell's total volume.
The endoplasmic reticulum comes in two types: Rough ER is covered with ribosomes and prepares newly made proteins; smooth ER specializes in making lipids and breaking down toxic molecules.
The endoplasmic reticulum comes in two types: Rough ER is covered with ribosomes and prepares newly made proteins; smooth ER specializes in making lipids and breaking down toxic molecules.
Smooth ER
Smooth ER
The endoplasmic reticulum comes in two types: Rough ER is covered with ribosomes and prepares newly made proteins; smooth ER specializes in making lipids and breaking down toxic molecules.
Take a closer look, and you'll see that the sacs are covered with bumps about 2 inches wide. Those bumps, called ribosomes, are sophisticated molecular machines made up of more than 70 proteins and 4 strands of RNA, a chemical relative of DNA. Ribosomes have a critical job: assembling all the cell's proteins. Without ribosomes, life as we know it would cease to exist.
To make a protein, ribosomes weld together chemical building blocks one by one. As naked, infant protein chains begin to curl out of ribosomes, they thread directly into the ER. There, hard-working enzymes clothe them with specialized strands of sugars.
Rough ER
Rough ER

Rough ER
SUSUMU ITO
Now, climb off the nucleus and out onto the ER. As you venture farther from the nucleus, you'll notice the ribosomes start to thin out. Be careful! Those ribosomes serve as nice hand- and footholds now. But as they become scarce or disappear, you could slide into the smooth ER, unable to climb out.
In addition to having few or no ribosomes, the smooth ER has a different shape and function than the ribosome-studded rough ER. A labyrinth of branched tubules, the smooth ER specializes in synthesizing lipids and also contains enzymes that break down harmful substances. Most cell types have very little smooth ER, but some cells—like those in the liver, which are responsible for neutralizing toxins—contain lots of it.
Next, look out into the cytosol. Do you see some free-floating ribosomes? The proteins made on those ribosomes stay in the cytosol. In contrast, proteins made on the rough ER's ribosomes end up in other organelles or are sent out of the cell to function elsewhere in the body. A few examples of proteins that leave the cell (called secreted proteins) are antibodies, insulin, digestive enzymes, and many hormones