Exam 1 Review:  Chapter 3 - Vesicular Transport

vesicular transport - The forms of active transport in which masses of molecules, as opposed to individual molecules, are moved across a cell membrane by the formation of a transport vesicle which carries the transported substances from one side of the membrane to the other by merging with or separating from the outer cell membrane; such movements can be either transport into or out of the cell; like all active transport processes, they require a significant input of chemical energy.

endocytosis - The type of vesicular transport in which extracellular materials are taken up by a cell through the mechanism of trapping a small droplet of the extracellular solution containing the desired materials in a membrane-bound vesicle formed from the outer cell membrane and transferring that vesicle into the cytoplasm; if this process includes the formation of pseudopods and can be seen in the light microscope, it is termed phagocytosis, and often involves the uptake of large solids such as the uptake of a bacterial cell by a white blood cell; if this process does not includes the formation of pseudopods and can only be seen in the electron microscope, it is termed pinocytosis, and involves the uptake of tiny liquid droplets with dissolved substances only.

exocytosis - The type of vesicular transport in which intracellular materials are transported out of a cell through the mechanism of merging a membrane-bound vesicle which contains a small droplet of the desired material(s), usually formed at the Golgi apparatus, which is moved to the undersurface of the outer cell membrane by elements of the cytoskeleton where the vesicle membrane merges with the outer cell membrane and releases the contents of the vesicle into the extracellular environment.

phagocytosis - The process of engulfing and ingesting microorganisms (viruses, bacteria, fungi, protozoans) or other foreign bodies or the cellular debris formed after any injury or tissue necrosis by cells specialized for this function; the phagocytes include neutrophils, eosinophils, monocytes and monocyte-derived macrophages of various sorts; the process involves diapedesis (amoeboid movement), pseudopod formation, and endocytosis to form an internal membrane bound organelle, the phagosome, where the engulfed organisms or substances can be chemically attacked; the structures formed in this type of endocytosis are large enough to be seen in the light microscope.

pseudopods - The temporary structures formed when cells capable of phagocytosis extend these membrane-covered extensions of their cytoplasm outward to cover the material to be engulfed; as the process continues, the structures merge to trap the external material in a vesicle, referred to as a phagocytic vesicle = phagosome; once the vesicle is formed, the cytoplasm is withdrawn until the cell takes up its original shape; these movements of cytoplasm and membrane are directed by elements of the cytoskeleton and require a significant input of chemical energy.

phagocytic vesicle - The membrane-bound droplet which forms when a phagocytic cell, such as certain white blood cells, has extended and merged its pseudopods around an object, such as a microorganism or cellular debris formed by a trauma, which it will transfer to the interior of the cell cytoplasm for further processing, usually for enzymatic degradation; this structure is generally large enough to be readily seen in the light microscope.  aka - phagosome.

phagocytes - Any cell which is capable of engulfing foreign material by extending and merging its pseudopods around an object, such as a microorganism or cellular debris formed by a trauma, which it will transfer to the interior of the cell cytoplasm for further processing, usually for enzymatic degradation; in humans these cells are generally certain classes of white blood cells, e.g., neutrophils, eosinophils, monocytes and monocyte-derived macrophages.

pinocytosis - The process of engulfing and ingesting minute droplets of the extracellular fluid including any dissolved solutes; many cells are capable of this process; the droplet is formed by the invagination of the outer cell membrane, directed by elements of the cytoskeleton and requiring a significant input of chemical energy; once inside, the engulfed substances can be chemically processed by the cell; the volume of liquid captured is small and this form of endocytosis can only be seen in the electron microscope.

pinocytotic vesicle - The membrane-bound droplet which forms when a cell has invaginated its outer cell membrane and "pinched off" a tiny droplet of extracellular solution, which it will transfer to the interior of the cell cytoplasm for further processing, usually for enzymatic degradation; this structure is too small to be seen in the light microscope.

receptor-mediated endocytosis - A special type of vesicular transport, endocytosis, in which specific molecules are transported into the cell with the aid of special membrane receptors (integral membrane proteins) which are located on the outer cell membrane; when the specific molecule binds (non-covalently) to the receptor, a receptor-ligand interaction, this receptor-ligand complex will migrate across the membrane surface to a point where a pinocytotic vesicle is forming; when a large number of these receptor-ligand complexes have arrived, endocytosis/pinocytosis begins, and the specific molecules are then packaged into a vesicle which will move to the interior of the cell cytoplasm; once there, the receptors release the ligand and the receptors will be transported ("recycled") back to the outer cell membrane to capture more of the ligand while the substance will be processed for use by the cell; an important example of this process is the capture of cholesterol-transporting low-density lipoproteins = LDLs.  See a diagramatic illustration of receptor-mediated endocytosis below:

secretory vesicles - Any of the large variety of membrane-bound packages of material (proteins synthesized by the rough ER, carbohydrates, lipids, or smaller organic molecules such as neurotransmitters and local hormones synthesized by the smooth ER) packaged by the Golgi apparatus which will be released from the cell by a process of exocytosis; the packaged material may be stored in these structures for varying periods of time and are often stored in inactive precursor form and not activated until just before, or after, exocytosis from the cell.

List:

8. four types of vesicular transport.