![]() ![]() It’s membrane is smooth and lack ribosomes. The smooth ER though forms a continuous system with the RER, has a different morphology. ![]() In general, RER is highly developed in cells of pancreas, liver, goblet cells, plasma cells etc. These proteins tend to interact with each other arid form intramembranous network, which control the ribosome binding sites in the plane of the ER membrane. Isolated RER contains two trans-membrane glycoproteins, such as ribophorin I and ribophorin II of molecular weighs 65,000 and 64,000 Daltons, respectively. The cells that are actively engaged in protein synthesis, such as plasma cells and goblet cells possess a dense macromolecular material inside the cisternae. The cavity of RER is sometimes very narrow, with two membranes closely apposed but more frequently there is a true space between the membranes that may be filled with a material of varying opacity. The ribosomes appear to be attached to the membrane by large 60 subunit. The ribosomes are present as polysomes held together by mRNA and are often arranged in typical ‘rosettes’ or ‘spirals’. RER is bounded by rough walls because ribosomes remain attached with its outer surface. Vesicles may often remain present in the cytoplasm of most cells (Fig. These two types of vesicles have different densities, indicating different nature of their contents. 3.9).įollowing homogenization of cells, the SER fragments into smooth- surfaced vesicles, whereas the RER fragments into rough-surfaced vesicles. Tubular form of ER is dynamic in nature, i.e., it is associated with membrane movements, fission and fusion between membranes of cytocavity network (Fig. It forms an interconnecting system of pipelines curving through the cytoplasm in which they occur. The membranous elements of SER are typically tubular. The size of ER varies considerably in different cell types and is related to their functions.Īlthough the cisternal space of the RER appears in electron micrograph to be divided into separate compartments, it is thought that all of the RER cisternae communicate with one another and that the cisternal space is continuous among them (Fig. On the other hand, cells of organs involved actively in protein synthesis (e.g., acinar cells of pancreas, goblet cells, cells of some endocrine glands) are found to contain RER that are highly developed. The adipose tissues, brown fat cells, adrenocortical cells and endocrine cells of testes and ovaries contain only SER. The erythrocytes, egg and embryonic cells lack ER. In hepatocytes, both SER (smooth ER) and RER (rough ER) are present. The occurrence of ER varies from cell to cell. The name ‘endoplasmic reticulum’ was first coined by Porter in 1953, who in 1945 had observed it in liver cells under electron microscope. ![]() These spaces or cavities often remain concentrated in the endoplasmic portion of the cytoplasm and therefore, is known as endoplasmic reticulum - ‘a net in the cytoplasm’ (Eighteenth-century European ladies carried purses of netting called reticules). ![]()
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