From protein synthesis to lipid metabolism to cell detoxification, the ER is involved in many processes within the cell. Cisternae, which are tiny folds of an endoplasmic reticulum, are frequently linked to lipid metabolism. The cell’s plasma membrane, as well as the endoplasmic reticulum and organelles, are formed as a result of this process. They furthermore appear to have a role in the cell’s Ca2+ balance and ER-mitochondrial interaction. The aerobic state of the cell is also affected by this interaction.
Because cells change their tubules-to-sheets ratio as the quantity of unfolded proteins increases, ER sheets appear to be important in the organelle’s response to stress. The ER can sometimes trigger apoptosis in reaction to too much unfolded protein in the cell. These structures can disseminate and generate tubular cisternae when ribosomes separate from ER sheets.
Although the activities of ER sheet and tubules appear to be separate, the roles are not completely defined. Tubules and sheets, for example, can interconvert in mammals, allowing cells to adapt to a variety of situations. In the ER, the relationship with both structure and function isn’t totally understood.
Protein Synthesis and Folding
Within the rough endoplasmic reticulum, proteins are synthesised. Although all proteins begin their translation in the cytoplasm, some of these are transported to the endoplasmic reticulum (ER) to also be folded or sorted for various purposes. During translation, proteins are frequently transferred into the ER and then secreted. These proteins are first folded in the ER before being transported to the Golgi apparatus, where they can be delivered to other organelles.
This is how the lysosome’s hydrolytic enzymes are made, for example. Alternatively, the cell may secrete these proteins. The enzyme of a digestive tract comes from this source. The third possible function of proteins translated inside the ER is to stay within the endomembrane system. This is especially true for chaperone proteins, which help other proteins fold correctly. When the cell is stressed by unfolded proteins, the genes that code for these proteins are increased.
The endoplasmic reticulum (ER) is required for the synthesis, packing, alteration, and transport of proteins, among other things. The two forms of ER, termed as rough ER (RER) and smooth ER, differ in a number of morphological and functional properties (SER). RER’s ribosomes, which give it its rough appearance, specialise in the synthesis of proteins with a signal sequence that sends them to the ER for processing. The RER’s proteins have specific destinations, such as with the cell membrane, the cell exterior, or the ER itself. SER is required for the synthesis of lipids, such as cholesterol and phospholipids, which also are required to make new cellular membranes.
Regulation of ER shape and function
The ER is a multi-functional organelle that is engaged in lipid and protein synthesis, calcium control, and interaction with other organelles. The physical architecture of the emergency room reflects the ER’s complexity. The nuclear envelope (NE) as well as the peripheral ER, which are characterised by sheet form and branched tubules, are both part of the ER’s continuous membrane system. A number of integral membrane proteins, as well as interaction with the other organelles as well as the cytoskeleton, influence the form and dispersion of these ER domains. These interactions are dynamic, reflecting changes inside the cell, such as cell cycle or developmental status, cell differentiation, intracellular signals, or protein interactions.
While the basic forms of ER sheets and tubules are well understood, how variations in form or the proportion of sheet to tubules happen in response to a particular cellular signal remains a mystery.
Improved imaging techniques have enabled the identification of distinct ER structures in specific cell types, as well as their ratios to one another. When comparing the functions of these cells in the organism, it’s evident that the kind and number of peripheral ER present matches that cell type’s function. It’s currently unknown how these ratios are calculated, or what cellular signalling pathways are involved in determining which ER type is most dominant in a given cell type.
Proteins promoting the development, maintenance, or stability of peripheral ER structures clearly interact with other proteins and structures, and all these interactions are essential for the appropriate assembly of the ER network. Interestingly, microtubules have been found to interact with several other proteins listed here.
Many cellular structures undergo drastic changes during mitosis in order to aid chromosomal segregation. Changes in the microtubule cytoskeleton as a result of enhanced microtubule dynamics generated by cyclin-dependent kinase activation are one of the most dramatic instances. The bipolar attachment of chromosomes to the mitotic spindle and correct segregation to daughter cells throughout anaphase are both dependent on the increases in microtubule dynamics throughout mitosis.
Conclusion
The endoplasmic reticulum is a web of tubules and flat vesicles that interact to form a network. There are two kinds of it. There are two types of endoplasmic reticulum: rough and smooth. A network of flat vesicles forms the rough endoplasmic reticulum. It comprises membrane proteins as well as ribosomes, which manufacture proteins for export. The tubules make up the smooth endoplasmic reticulum. Because it lacks ribosomes, it’s smooth. It plays a role in lipid synthesis, detoxification, and Ca2+ storage as part of the sarcoplasmic reticulum.