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Endoplasmic reticulum - Wikipedia

What determines whether a particular mRNA molecule is translated by ribosomes that are free in the cytosol or by ribosomes that are attached to the RER? The answer lies again in the amino acid sequence of the protein being synthesised. In fact, translation of all eukaryotic mRNAs starts on 'free' ribosomes in the cytosol (Figure 18a), but if an mRNA encodes a protein that is destined for lysosomes, or to be secreted from the cell, or to be embedded in a cell membrane, the ribosome is rapidly redirected to the endoplasmic reticulum by a process known as . As soon as the beginning of the translated polypeptide (which is known as the N-terminus, or amino (NH2) terminus) starts to emerge from the free ribosome, a signal sequence for localisation to the RER, close to the N-terminus, is recognised by a protein complex called the (SRP). Translation pauses, and the whole complex, including the ribosome, mRNA and partially translated polypeptide, is transported to the membrane of the RER. There, translation recommences and the growing polypeptide chain is simultaneously translocated across the membrane of the RER and starts to enter the RER lumen, the space inside the RER (Figure 18c).

SER does not contain this cell organelle, and hence the name smooth endoplasmic reticulum.

Another type of endoplasmic reticulum is Sarcoplasmic Reticulum, which is a type of specialized SER that can be found in smooth, as well as striated muscles.

Rough Endoplasmic Reticulum - BiologyWise

The Endoplasmic Reticulum that does not have Ribosomes attached to its surface is known as smooth endoplasmic reticulum.

If you were looking for a rough endoplasmic reticulum analogy, then you can very well relate it to a highway with intermittent stations, where the proteins are being synthesized and transported to the cell membrane.

Rough Endoplasmic Reticulum (RER) Facts

Structure

Rough ER is made up of convoluted and sealed sacs, which are studded with membrane-bound ribosomes on the outer surface.

The entire structure has an interior space, which is also known as endoplasmic reticulum cisternal space, or lumen, which comprises 10% of the cell volume.

Endoplasmic reticulum - an overview | ScienceDirect Topics

However, this organelle is constituted of three layers: rough endoplasmic reticula (synthesizes proteins), smooth endoplasmic reticulum (synthesizes and metabolizes lipids and steroids, and regulates calcium concentration), and sarcoplasmic reticulum (regulates calcium levels).

ER is an intense network of interconnected tubules, vesicles, and fluid-filled sacs surrounding the nuclear membrane, which spreads all across the cell cytoplasm.

Some parts of the endoplasmic reticulum appear smooth when viewed by EM and are hence named (SER). Smooth endoplasmic reticulum is involved in the production of phospholipids and steroids and also in the detoxification of substances such as drugs or ingested chemicals. Ingestion of large amounts of a toxic substance, such as a pesticide, results in an increase in the amount of SER in cells. Normally, however, most of the endoplasmic reticulum appears granular, being dotted with many ribosomes (Figure 17). This part of the endoplasmic reticulum is given the name , and is the site where lysosomal proteins (mainly digestive enzymes), membrane proteins, and proteins that are destined for export from the cell are synthesised and processed.

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All About the Smooth Endoplasmic Reticulum and its …

Basically, a eukaryotic cell consists of a well-formed nucleus and membrane-bound organelles, unlike the prokaryotes, which are devoid of both.

About 50% of the total surface of the eukaryotic cell is constituted by the cell organelles known as endoplasmic reticulum (ER).

Protein synthesis in the endoplasmic reticulum - YouTube

Lai E, Teodoro T and Volchuk A:Endoplasmic reticulum stress: Signaling the unfolded proteinresponse. Physiology (Bethesda). 22:193–201. 2007. : :

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