Smooth endoplasmic reticulum
Smooth endoplasmic reticulum (SER), meshwork of fine disklike tubular membrane vesicles, part of a continuous membrane organelle within the cytoplasm of eukaryotic cells, that is involved in the synthesis and storage of lipids, including cholesterol and phospholipids, which are used in the production of new cellular membrane. Oct 04, †Ј Smooth Endoplasmic Reticulum Definition. The smooth endoplasmic reticulum (smooth ER) is a membranous organelle found in most eukaryotic cells. It is a subset of the endomembrane system of the endoplasmic reticulum. Its main functions are the synthesis of lipids, steroid hormones, the detoxification of harmful metabolic byproducts and the storage and metabolism of calcium ions within .
Smooth endoplasmic reticulum SERmeshwork of fine disklike tubular membrane vesicles, part of a continuous smolth organelle within the cytoplasm of eukaryotic cellsthat is involved in the synthesis and storage of lipidsincluding cholesterol and phospholipidswhich are used in the production of new cellular membrane.
SER occurs both in animal and in plant cells. The function q the SER can vary, depending on cell type. In some cells, such as those of the adrenal gland and certain other endocrine glands, it plays a key role in the synthesis of steroid hormones from cholesterol. In the liverenzymes in the SER catalyze reactions that render drugsmetabolic wastes, what is a smooth e. r harmful chemicals water-soluble, thereby contributing to their detoxificationor removal, from the body.
The SER also plays a role in the conversion of glycogen to glucosewith glucosephosphatase, an enzyme present in SER, catalyzing the final step in glucose production in the liver. In skeletal muscle cells, SER occurs as a specialized membrane structure known as the sarcoplasmic reticulum. The sarcoplasmic reticulum is a critical storage site for calcium smolthtaking up the e. from the cytoplasm. Whst also releases calcium ions when the muscle cell is whxt by nerve stimuli, resulting in muscle contraction.
In this way, the sarcoplasmic reticulum helps regulate calcium ion concentrations in the cytoplasm of skeletal muscle cells. The sarcoplasmic reticulum is also found in smooth muscle cells, though in a more loosely organized form than in skeletal muscle.
Smooth endoplasmic reticulum. Additional Info. More About Contributors Article History. Print Cite verified Cite. While every effort has been made to follow citation style rules, there may be some discrepancies. Please refer to the appropriate style manual or other sources if skooth have any questions.
Facebook Twitter. Give Feedback External Websites. Let us know if you have suggestions to improve this article requires login. External Websites. She joined Britannica in and See Article History. Endoplasmic reticulum, a continuous membrane system in eukaryotic cells that plays an important role in the biosynthesis, processing, and transport of proteins and lipids.
Read More on This Topic. The functions of the SER, a meshwork of fine tubular membrane vesicles, vary considerably from cell to cell. One important role is the synthesis Learn More in these related Britannica articles:. One shat role is the synthesis of phospholipids and cholesterol, which are major components of the plasma and internal membranes. Phospholipids are formed how to send 500mb file through email. The tubules can also enter the axon at its initial segment and extend to the axon terminals.
Wyat ER, by contrast, is not associated with how to cite an organization, and its functions differ. The smooth ER is involved in the synthesis of lipids, including cholesterol and phospholipids, which are used in the production of new cellular membrane.
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May 22, †Ј The smooth endoplasmic reticulum, or smooth ER, is an organelle found in both animal cells and plant cells. An organelle is a sub-unit within a cell that has a specialized function. Quick look. Rough ER (RER) is involved in some protein production, protein folding, quality control and despatch. It is called СroughТ because it is studded with ribosomes. Smooth E R (SER) is associated with the production and metabolism of fats and steroid hormones. It is СsmoothТ because it is not studded with ribosomes and is associated with smooth slippery fats. Jan 23, †Ј The smooth ER (endoplasmic reticulum) function involves manufacturing and packaging, including the synthesis of lipids and hormones which are used for the production of new cellular membranes. The rough ER (endoplasmic reticulum) function involves the assembly of proteins and the transportation of those assembled ready proteins to where they will be used by the .
To view a micrograph of ER interpreted using the Gridpoint cross-hairs device, click here. This statement certainly applies to the endoplasmic reticulum an organelle found in eukaryotic cells. Many of these products are made for and exported to other organelles.
This is an electron microscope image showing part of the rough endoplasmic reticulum in a plant root cell from maize. The dark spots are ribosomes. There are two types of endoplasmic reticulum: rough endoplasmic reticulum rough ER and smooth endoplasmic reticulum smooth ER. Both types are present in plant and animal cells. The two types of ER often appear as if separate, but they are sub-compartments of the same organelle. Cells specialising in the production of proteins will tend to have a larger amount of rough ER whilst cells producing lipids fats and steroid hormones will have a greater amount of smooth ER.
Part of the ER is contiguous with the nuclear envelope. The Golgi apparatus is also closely associated with the ER and recent observations suggest that parts of the two organelles, i. This is an extensive organelle composed of greatly convoluted but flattish sealed sacs, which are contiguous with the nuclear membrane.
These are called membrane bound ribosomes and are firmly attached to the outer cytosolic side of the ER About 13 million ribosomes are present on the RER in the average liver cell. Rough ER is found throughout the cell but the density is higher near the nucleus and the Golgi apparatus.
This process is called translation. Certain cells of the pancreas and digestive tract produce a high volume of protein as enzymes. Many of the proteins are produced in quantity in the cells of the pancreas and the digestive tract and function as digestive enzymes. Proteins are produced for the plasma membrane, Golgi apparatus, secretory vesicles, plant vacuoles, lysosomes, endosomes and the endoplasmic reticulum itself.
Some of the proteins are delivered into the lumen or space inside the ER whilst others are processed within the ER membrane itself. In the lumen some proteins have sugar groups added to them to form glycoproteins.
Some have metal groups added to them. It is in the rough ER for example that four polypeptide chains are brought together to form haemoglobin. Protein quality control section It is also in the lumen that an amazing process of quality control checking is carried out.
Proteins are subjected to a quality control check and any that are found to be incorrectly formed or incorrectly folded are rejected. These rejects are stored in the lumen or sent for recycling for eventual breakdown to amino acids.
A type of emphysema a lung problem is caused by the ER quality control section continually rejecting an incorrectly folded protein. The protein is wrongly folded as a result of receiving an altered genetic message. The required protein is never exported from the lumen of rough ER. Rigorous quality control plays a part in cystic fibrosis A form of cystic fibrosis is caused by a missing single amino acid, phenylanaline, in a particular position in the protein construction.
The protein might work well without the amino acid but the very exacting service provided by the quality control section spots the error and rejects the protein retaining it in the lumen of the rough ER. In this case the customer the person with cystic fibrosis loses out completely due to high standards when a slightly poorer product would have been better than no product at all. They are conveyed in vesicles or possibly directly between the ER and Golgi surfaces.
It is found fairly evenly distributed throughout the cytoplasm. Smooth ER is devoted almost exclusively to the manufacture of lipids and in some cases to the metabolism of them and associated products. In liver cells for example smooth ER enables glycogen that is stored as granules on the external surface of smooth ER to be broken down to glucose. Smooth ER is also involved in the production of steroid hormones in the adrenal cortex and endocrine glands. Smooth ER Ч the detox stop Smooth ER also plays a large part in detoxifying a number of organic chemicals converting them to safer water-soluble products.
Large amounts of smooth ER are found in liver cells where one of its main functions is to detoxify products of natural metabolism and to endeavour to detoxify overloads of ethanol derived from excess alcoholic drinking and also barbiturates from drug overdose. To assist with this, smooth ER can double its surface area within a few days, returning to its normal size when the assault has subsided. The contraction of muscle cells is triggered by the orderly release of calcium ions. These ions are released from the smooth endoplasmic reticulum.
Cytoskeleton Ч the movers and shapers in the cell. Extracellular Matrix and Cell Adhesion Molecules. Endoplasmic reticulum is an organelle found in both eukaryotic animal and plant cells. It often appears as two interconnected sub-compartments, namely rough ER and smooth ER. Both types consist of membrane enclosed, interconnected flattened tubes. The rough ER, studded with millions of membrane bound ribosomes, is involved with the production, folding, quality control and despatch of some proteins.
Smooth ER is largely associated with lipid fat manufacture and metabolism and steroid production hormone production. It also has a detoxification function.