In biology an endosome is a membrane-bound compartment inside cells. Many endocytotic vesicles derived from the plasma membrane are transported to an endosome and fuse with it. Some endocytosed material passes through endosomes on its way to lysosomes. Main articles: Life The most salient example of biological universality is that all living things share a common carbon-based biochemistry and in particular pass on their characteristics via genetic material, which is based on nucleic acids such as DNA and which uses a common genetic code with only minor... Jump to: navigation, search sperm is a process whereby cells absorb material (molecules or other cells) from outside by engulfing it with their cell membranes. ... Drawing of a cell membrane A component of every biological cell, the cell membrane (or plasma membrane) is a thin and structured bilayer of phospholipid and protein molecules that envelopes the cell. ... Jump to: navigation, search Lysosomes contain digestive enzymes (acid hydrolases) to digest macromolecules. ...

Many endocytic vesicles originate at the cell surface as clathrin-coated pits. As clathrin assembles under a patch of plasma membrane the clathrin-coated pit soon (about a minute) pinches off from the surface and forms a clathrin-coated endocytotic vesicle. Soon after forming, the clathrin coated vesicles release their associated clathrin and become competent to fuse with early endosomes. Extracellular materials trapped in the endocytic vesicles can either be passed into the endosomal compartment or returned to the surface. Clathrin is a protein that is the major constituent of the coat of the coated pits and coated vesicles formed during endocytosis of materials at the surface of cells. ...

Some materials are specifically endocytoced by receptor-mediated endocytosis. Some extracellular molecules bind to transmembrane receptor proteins that efficiently accumulate in coated pits. One physiologically important example of receptor-mediated endocytosis is the main mechanism by which cholesterol is taken up by cells, particularly liver cells. In some people the cholesterol receptor is defective, uptake of cholesterol from the blood into liver cells is slow and cholesterol accumulating in the blood and can damage blood vessel walls resulting in strokes and heart attacks at a young age. Short signal peptides have been identified that target certain transmembrane proteins into clathrin-coated pits. A set of proteins called adaptins bind the signal peptides. The signal for the cholesterol recptor is the tetrapeptide Asn-Pro-Val-Tyr. Receptor may refer to: In telecommunication, a receiver. ... Jump to: navigation, search Cholesterol is a steroid, a lipid, and an alcohol, found in the cell membranes of all body tissues, and transported in the blood plasma of all animals. ...

Microscopy indicates that in some cells the endosomal compartments is a network of membranous tubes and vesicles extending all the way to the nucleus. The deep end of the endosomal compartment is called the late endosome compartment. It may take 5-15 minutes for materials to be transported from the cell surface through early endosome compartments and on to the late endosome. The endosomal compartment is usually acidic due to the action of a proton-pumping ATPase of the endosomal membrane. Many receptors involved in endocytosis of extracellular substances change their conformation at low pH and release their bound substance. The empty receptor proteins can then be sorted back to the cell surface. Jump to: navigation, search Nucleus can mean: The Nuclear Envelope The nucleus is enveloped by a pair of membranes enclosing a lumen that is continuous with that of the endoplasmic reticulum. ...

Some materials that reach the late endosomes are degraded in lysosomes. Parts of the late endosomal compartment may become lysosomes or temporarily fuse with lysosomes in order to transfer endoctosed materials into the lysosomes. In epithelial cells a special process called transcytosis allows some materials to enter one side of a cell and exit from the opposite side. For example, the GI tract of babies can take protective antibody proteins from breast milk and via transcytosis, transport the antibodies into the blood stream. Jump to: navigation, search In zootomy, epithelium is a tissue composed of a layer of cells. ... Jump to: navigation, search Schematic of antibody binding to an antigen An antibody is a protein used by the immune system to identify and neutralize foreign objects like bacteria and viruses. ...

A cell surface transferrin receptor binds the iron transport protein transferrin in another example of receptor-mediated endocytosis. In the acidic endosome, the iron is released from transferrin and then the iron-free transferrin (still bound the transferrin receptor) returns from the early endosome to the cell surface. Jump to: navigation, search General Name, Symbol, Number iron, Fe, 26 Chemical series transition metals Group, Period, Block 8, 4, d Appearance lustrous metallic with a grayish tinge Atomic mass 55. ... Transferrin is a protein for iron ion delivery. ...