Endoplasmic Reticulum Structure Rough ER Smooth ER

Figure 1 : Image of nucleus, endoplasmic reticulum and Golgi apparatus.
(1) Nucleus. (2) Nuclear pore. (3) Rough endoplasmic reticulum (RER). (4) Smooth endoplasmic reticulum (SER). (5) Ribosome on the rough ER. (6) Proteins that are transported. (7) Transport vesicle. (8) Golgi apparatus. (9) Cis face of the Golgi apparatus. (10) Trans face of the Golgi apparatus. (11) Cisternae of the Golgi apparatus.

The ER consists of an extensive membrane network of tubes and cisternaThis article relates to cell biology. For the Italian town, see Cisterna, Italy. A cisterna (plural cisternae comprises a flattened membrane disk which makes up the Golgi apparatus. A typical Golgi has anywhere from 3 to 7 cisternae stacked upon each othee (sac-like structures). The membrane encloses a space, the cisternal space (or internal lumen) from the cytosolThe cytosol (as opposed to cytoplasm which also includes the organelles) is the internal fluid of the cell, and a large part of cell metabolism occurs here. Proteins within the cytosol play an important role in signal transduction pathways, glycolysis, an. This space is acting as a gateway. Parts of the ER membrane are continuous with the outer membrane of the nuclear envelopeThe nuclear envelope refers to the double membrane of the nucleus that encloses genetic material in eukaryotic cells. It separates the contents of the nucleus ( DNA in particular) from the cytosol. The space between the two membranes that make up the nucl, and the cisternal space of the ER is continuous with the space in between the two layers of the nuclear envelope.

Parts of the ER are covered with ribosomeA ribosome is an organelle composed of rRNA (synthesized in the nucleolus) and ribosomal proteins. It translates mRNA into a polypeptide chain (e. a protein). It can be thought of as a factory that builds a protein from a set of genetic instructions.s (which assemble amino acids into proteins based on instructions from the nucleus). Their rough appearance under electron microscopy led to their being called rough ER (RER), other parts are free of ribosomes and are called smooth ER (SER). The ribosomes on the surface of the rough ER insert the freshly produced proteins directly into the ER, which processes them and then passes them on to the Golgi apparatusIn cell biology, the Golgi apparatus Golgi complex or dictyosome is an organelle found in nearly all eukaryotic cells. The name comes from Italian anatomist Camillo Golgi, who identified it in 1898. Its primary function is to process proteins targeted to (Fig. 1). Rough and smooth ER differ not only in appearance, but also in function.

1.1 Rough ER

The coarse ER manufactures and transports proteins destined for membranes and secretion. It synthesizes membrane, organellar, and excreted proteins. Minutes after proteins are synthesized most of them leave to the Golgi apparatusIn cell biology, the Golgi apparatus Golgi complex or dictyosome is an organelle found in nearly all eukaryotic cells. The name comes from Italian anatomist Camillo Golgi, who identified it in 1898. Its primary function is to process proteins targeted to within vesicleIn cell biology, a vesicle is a relatively small and enclosed compartment, separated from the cytosol by at least one lipid bilayer. Vesicles store, transport, or digest cellular products and wastes. This biomembrane enclosing the vesicle is the same as ts. The rough ER also modifies, folds, and controls the quality of proteins.

1.2 Smooth ER

The smooth ER has functions in several metabolic processes. It takes part in the synthesis of various lipidLipids are fatty acid esters, a class of relatively water-insoluble organic molecules, which are the "basic" components of biological membranes. There are three forms of lipids: phospholipids, steroids. and triglycerides. Lipids consist of a polar or hydrs (e.g., for building membranes such as phospholipids), fatty acids and steroids (e.g., hormones), and also plays an important role in carbohydrate metabolism, detoxification of the cell (enzymes in the smooth ER detoxify chemicals), and calcium storage.It also is a large tranporter of nutrient found in each cell.

2 Functions

The endoplasmic reticulum serves many general functions, including the facilitation of protein folding, and the transport of proteins. Correct folding of newly made proteins is made possible by several ER proteins including: PDI, Hsc70 family , calnexin , calreticulin, and the peptidylpropyl isomerase family . Only properly folded proteins are transported from the RER to the Golgi complex.

2.1 Transport of proteins

Secretory proteins are moved across the ER membrane. Proteins that are transported by the ER and from there throughout the cell are marked with an address tag that are called a signal sequence. Günter Blobel was awarded the 1999 Nobel Prize in Physiology or Medicine for his discovery of these signal sequences in 1975. The N-terminus (one end) of a polypeptide chain (e.g., a protein) contains a few amino acids that work as an address tag, which are removed when the polypeptide reaches its destination. Proteins that are destined for places outside the ER are packed into transport vesicles and moved along the cytoskeleton towards their destination. The ER is also part of a protein sorting pathway.

2.2 Other functions

Insertion of proteins into the ER membrane. Integral proteins need to be inserted into the ER membrane after they are synthesized. Insertion into the ER membrane requires the correct topogenic sequences.
Glycosylation. Glycosylation involves the attachment of oligosaccharides .
Disulfide bond formation and rearrangement. Disulfide bonds stabilize the tertiary and quaternary structure of many proteins.
Sarcoplasmic reticulum. The endoplasmic reticulum found in muscle fibers is called sarcoplasmic reticulum.

Organelles of the cell
Chloroplast \| Mitochondrion \| Centriole \| Endoplasmic reticulum \| Golgi apparatus \| Lysosome \| Myofibril \| Nucleus \| Peroxisome \| Ribosome \| Vacuole \| Vesicle

Organelles

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1 Structure