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A lysosome (/ ˈ l aɪ s ə ˌ s oʊ m /) is a single membrane-bound organelle found in many animal cells. [1] [2] They are spherical vesicles that contain hydrolytic enzymes that digest many kinds of biomolecules. A lysosome has a specific composition, of both its membrane proteins and its lumenal proteins.
For example, in epithelial cells, a special process called transcytosis allows some materials to enter one side of a cell and exit from the opposite side. Also, in some circumstances, late endosomes/MVBs fuse with the plasma membrane instead of with lysosomes, releasing the lumenal vesicles, now called exosomes, into the extracellular medium.
Lysosomes provide such an environment by maintaining a pH of 5.0 inside of the organelle. [37] If a lysosome were to rupture, the enzymes released would not be very active because of the cytosol's neutral pH. However, if numerous lysosomes leaked the cell could be destroyed from autodigestion.
A vesicle released from the cell is known as an extracellular vesicle. Vesicles perform a variety of functions. Because it is separated from the cytosol, the inside of the vesicle can be made to be different from the cytosolic environment. For this reason, vesicles are a basic tool used by the cell for organizing cellular substances.
Residual bodies are either secreted by the cell via exocytosis (this generally only occurs in macrophages), or they become lipofuscin granules that remain in the cytosol indefinitely. Longer-living cells like neurons and muscle cells usually have a higher concentration of lipofuscin than other more rapidly proliferating cells.
The nucleolus within the nuclear envelope is the location of ribosome synthesis. The destination of synthesized ribosomes for protein translation is rough endoplasmic reticulum (rough ER), which is connected to and shares the same membrane with the nucleus. The Golgi body is also near the rough ER for packaging and redistributing. Likewise ...
The process of phagocytosis showing phagolysosome formation. Lysosome(shown in green) fuses with phagosome to form a phagolysosome. Membrane fusion of the phagosome and lysosome is regulated by the Rab5 protein, [1] a G protein that allows the exchange of material between these two organelles but prevents complete fusion of their membranes. [1]
Autophagy (or autophagocytosis; from the Greek αὐτόφαγος, autóphagos, meaning "self-devouring" [1] and κύτος, kýtos, meaning "hollow") [2] is the natural, conserved degradation of the cell that removes unnecessary or dysfunctional components through a lysosome-dependent regulated mechanism. [3]