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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.
The main functions of a lysosome are to process molecules taken in by the cell and to recycle worn out cell parts. The enzymes inside of lysosomes are acid hydrolases which require an acidic environment for optimal performance. Lysosomes provide such an environment by maintaining a pH of 5.0 inside of the organelle. [37]
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.
Cellular compartments in cell biology comprise all of the closed parts within the cytosol of a eukaryotic cell, usually surrounded by a single or double lipid layer membrane. These compartments are often, but not always, defined as membrane-bound organelles. The formation of cellular compartments is called compartmentalization.
The Golgi apparatus is a major collection and dispatch station of protein products received from the endoplasmic reticulum. Proteins synthesized in the ER are packaged into vesicles, which then fuse with the Golgi apparatus. These cargo proteins are modified and destined for secretion via exocytosis or for use in the cell.
Golgi apparatus: The primary function of the Golgi apparatus is to process and package the macromolecules such as proteins and lipids that are synthesized by the cell. Lysosomes and peroxisomes: Lysosomes contain digestive enzymes (acid hydrolases). They digest excess or worn-out organelles, food particles, and engulfed viruses or bacteria.
The lysosomal enzymes are then delivered to the lysosomes for their final role in cellular degradation. [ 7 ] Thus, the secretory pathway is a highly coordinated process, involving various vesicular transport mechanisms and modifications, to ensure that proteins are correctly sorted, processed, and delivered to their appropriate cellular locations.
Once the enzyme has dissociated from the mannose 6-phosphate receptor, it is translocated from the endosome to the lysosome where the phosphate tag is removed from the enzyme. MPRs are not found in the lysosomes; they cycle mainly between the trans-Golgi network and endosomes. The CI-MPR is also present on the cell surface.