RER is mostly made of cistemae. Tubules are very few. Endoplasmic reticulum consists of membrane lined channels or spaces. The channels or spaces contain a fluid called endoplasmic matrix, which is quite different from cytoplasmic matrix present outside the reticulum.
The membranes of endoplasmic reticulum are A thick. Endoplasmic reticulum can exist in three forms Fig. They are flat interconnected sac-like parts of the endoplasmic reticulum which are nm in diameter. The cisternae are found in bundles where they lie parallel to one another. They occur in the cells actively involved in synthetic activity. They are oval or rounded sacs of nm in diameter. The vesicles appear as small vacuoles.
They remain isolated in the cytoplasm. The vesicles are also called microsomes. It functions as cytoskeleton or intracellular and ultra-structural skeletal framework by providing mechanical support to colloidal cytoplasmic matrix. Endoplasmic reticulum as desmotubules controls movement of materials between two adjacent protoplasts through plasmodesmata. In cells, endoplasmic reticulum conducts information from cell exterior to inside and from one part of the cell to another, e.
The membranes of endoplasmic reticulum contain a number of enzymes e. It bears enzymes in the region of pores for modifying polypeptides synthesised by attached ribosomes, e. Proteins and enzymes synthesised by ribosomes enter the channels of RER both for intracellular use as well as secretion.
It is responsible for synthesis of fats inside the cells of adipose tissue, formation of sphaerosomes, synthesis of glycogen as well as glycogenolysis hydrolysis of glycogen in liver cells for this, SER possesses enzyme bodies called glycosomes synthesis of ascorbic acid, synthesis of sterols and steroid hormones as in the interstitial cells of testis and ovary and formation of visual pigments from vitamin A in retinal cells.
Biology , Cell , Endoplasmic Reticulum , Organelles. Top Menu BiologyDiscussion. Difference between Microfilaments and Microtubules Cytoskeletal Structure. Essay on Nucleus: Structure, Position and Functions. This is a question and answer forum for students, teachers and general visitors for exchanging articles, answers and notes. Answer Now and help others.
Answer Now. Here's how it works: Anybody can ask a question Anybody can answer The best answers are voted up and rise to the top. English and Gia K. Mandon, Steven F. Hutt and William E. The endoplasmic reticulum is one of the most intriguing and fascinating organelles. It is found in all eukaryotic cells and performs an amazing number of different functions. The organelle was named by Keith Porter in on the basis of observations made with the electron microscope on tissue culture cells.
The ER is the main site for the synthesis of sterols and phospholipids that constitute most of the lipid components of all biological membranes. In addition, many enzymes and regulatory proteins involved in lipid metabolism reside in the ER.
The ER, therefore, plays an essential role in the control of the lipid composition of the membrane [ 6 ] and the lipid homeostasis of the membrane in all cell types. Stearoyl-CoA desaturase is a microsomal oxidase system required for the biosynthesis of oleic acid. Three protein components of this system cytochrome b5 reductase, cytochrome bs, and terminal oxidase were resolved, and an enzymatically active desaturase was reconstituted from the purified components.
As a result of these studies, an article was published in J. Stearoyl-CoA desaturase SCD is an enzyme of the endoplasmic reticulum ER that catalyzes the biosynthesis of monounsaturated fatty acids MUFAs from saturated fatty acids that are synthesized again or derived from the diet. The SCD along with NADH, the flavoprotein cytochrome b5 reductase, and the electron acceptor cytochrome b5 as well as the molecular oxygen introduced a simple double bond in a spectrum of acyl-CoA fatty substrates interrupted with methylene Figure 1.
The preferred substrates are palmitoyl- and stearoyl-CoA, which are then converted into palmitoleoyl- and oleoyl-CoA, respectively [ 7 ]. These products are the most abundant monounsaturated fatty acids MUFAs and serve as substrates for the synthesis of various kinds of lipids, including phospholipids, triglycerides TG , cholesteryl esters, wax esters, and alkyldiacylglycerols.
Apart from being the components of lipids, MUFAs have also been implicated to serve as mediators in signal transduction and cellular differentiation, including neuronal differentiation [ 8 ].
Recently, oleate has been shown to regulate food intake in the brain [ 9 ], and MUFAs may also influence apoptosis and mutagenesis in some tumors [ 10 ]. Thus, given the multiple roles of MUFAs, variation in stearoyl-CoA desaturase activity in mammals would be expected to influence a variety of key physiological variables, including cellular differentiation, insulin sensitivity, metabolic rate, adiposity, atherosclerosis, cancer, and obesity. It has been fascinating to follow the field of endoplasmic reticulum research during almost six decades.
Quantitative proteomics and lipidomics analysis are now available for measurement of the main components of the endoplasmic reticulum. From my experience, it is impossible to predict which aspects in endoplasmic reticulum research will dominate in the future. This book is dedicated to the memory of Emeritus Professor Dr.
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