::Lysosome

::concepts

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{{#invoke:Infobox|infobox}} A lysosome (derived from the Greek words lysis, meaning "to loosen", and soma, "body") is a membrane-bound cell organelle found in most animal cells (they are absent in red blood cells). Structurally and chemically, they are spherical vesicles containing hydrolytic enzymes capable of breaking down virtually all kinds of biomolecules, including proteins, nucleic acids, carbohydrates, lipids, and cellular debris. They are known to contain more than 50 different enzymes, which are all optimally active at an acidic environment of about pH 4.5 (about the pH of black coffee). Thus lysosomes act as the waste disposal system of the cell by digesting unwanted materials in the cytoplasm, both from outside of the cell and obsolete components inside the cell. For this function they are popularly referred to as "suicide bags" or "suicide sacs" of the cell.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=book }}</ref> Furthermore, lysosomes are responsible for cellular homeostasis for their involvements in secretion, plasma membrane repair, cell signalling and energy metabolism, which are related to health and diseases.<ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref> Depending on their functional activity, their sizes can be very different—the biggest ones can be more than 10 times bigger than the smallest ones.<ref>{{#invoke:citation/CS1|citation |CitationClass=book }}</ref> They were discovered and named by Belgian biologist Christian de Duve, who eventually received the Nobel Prize in Physiology or Medicine in 1974.

Enzymes of the lysosomes are synthesised in the rough endoplasmic reticulum. The enzymes are released from Golgi apparatus in small vesicles which ultimately fuse with acidic vesicles called endosomes, thus becoming full lysosomes. In this process, the enzymes are specifically tagged with the molecule mannose 6-phosphate to differentiate them from other enzymes. Lysosomes are interlinked with three intracellular processes, namely phagocytosis, endocytosis and autophagy. Extracellular materials such as microorganisms taken up by phagocytosis, macromolecules by endocytosis, and unwanted cell organelles are fused with lysosomes in which they are broken down to their basic molecules. Thus lysosomes are the recycling units of a cell.<ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref>

Synthesis of lysosomal enzymes is controlled by nuclear genes. Mutations in the genes for these enzymes are responsible for more than 30 different human genetic diseases, which are collectively known as lysosomal storage diseases. These diseases are due to deficiency in a single lysosomal enzyme, that prevents breakdown of target molecules; consequently the undegraded materials accumulate within the lysosomes and often giving rise to severe clinical symptoms. Further, such genetic defects are related to several neurodegenerative disorders, cancer, cardiovascular diseases, and ageing-related diseases.<ref name=platt>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref><ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref>


Lysosome sections
Intro  Discovery   Function and structure    Formation   Disease   Lysosomotropism    Controversy in botany   See also  References  External links  

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