TY - CHAP M1 - Book, Section TI - The Cytoplasm A1 - Mescher, Anthony L. PY - 2021 T2 - Junqueira's Basic Histology Text and Atlas, 16e AB - The Cytoplasm SUMMARY OF KEY POINTSCell differentiation is the process by which cells of an embryo become specialized structurally to augment specific cytoplasmic activities for functions at the level of tissues and organs.Organelles are metabolically active structures or complexes, with or without membranes, in the cytoplasm of eukaryotic cells.Plasma MembraneThe plasma membrane (cell membrane or plasmalemma) is the lipid bilayer with embedded proteins that surrounds a cell and is seen only with the TEM.The lipid bilayer forms from amphipathic phospholipids, stabilized by cholesterol, and contains many embedded (integral) proteins and many peripheral proteins on its cytoplasmic surface.Membrane proteins move laterally within the lipid bilayer, with less movement in areas referred to as lipid rafts, which have higher concentrations of cholesterol and saturated fatty acids.Integral membrane proteins include receptors for external ligands, channels for passive or active movement of molecules across the membrane, and pumps for active membrane transport.Endocytosis is cellular uptake of macromolecules or fluid by plasma membrane engulfment or invagination, followed by the “pinching off” of a filled membranous vesicle in the cytoplasm.Major types of endocytosis include phagocytosis (uptake of particulate material), pinocytosis (uptake of dissolved substances), and receptor-mediated endocytosis (uptake of specific molecules bound to integral membrane receptor proteins).Exocytosis is a type of cellular secretion in which cytoplasmic membrane vesicles fuse with the plasma membrane and release their contents to the extracellular space.All types of cell signaling use membrane receptor proteins that are often linked to enzymes such as kinases or adenylyl cyclase whose activities initiate intracellular signaling pathways.RibosomesThe two ribosomal subunits, each a complex of rRNA and many proteins, attach to mRNA and translate that message into protein.Multiple ribosomes on the same mRNA make up a polyribosome (polysome), and an abundance of these produces basophilic cytoplasm after H&E staining.Endoplasmic ReticulumThe ER is a convoluted network of membrane enclosing continuous spaces called cisternae and extending from the nucleus to the plasma membrane.Rough ER has a granular, basophilic cytoplasmic surface due to the presence of polysomes making most membrane proteins, proteins in certain other organelles, or for exocytosis; RER is always well developed in cells actively secreting proteins.Proteins to be processed through the RER contain initial signal peptides that bind receptors in the ER membrane, localizing them to that organelle.After translocation across the membrane into the cisterna, the proteins undergo posttranslational modification and folding in a process monitored by RER molecular chaperones and enzymes.Smooth ER (SER) lacks ribosomes but includes enzymes for lipid and glycogen metabolism, for detoxification reactions, and for temporary Ca2+sequestration.Golgi ApparatusThe Golgi apparatus is a dynamic organelle consisting of stacked membranous cisternae in which proteins made in RER are processed further and packaged for secretion or other roles.Proteins in transport vesicles enter the cis or receiving face of the Golgi, move through medical cisternae of the Golgi network for enzymatic modifications, and are released in other vesicles at the trans face.Vesicle movement through the Golgi apparatus is guided by specific coat proteins such as COPII and COPI.Important protein modifications in the Golgi apparatus include sulfation and many glycosylation ... SN - PB - McGraw Hill CY - New York, NY Y2 - 2024/03/28 UR - accessmedicine.mhmedical.com/content.aspx?aid=1184199178 ER -