lysosomes

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Various organelles labeled. The lysosome is labeled in the upper left.


Lysosomes are organelles that contain digestive enzymes (acid hydrolases). They digest excess or worn out organelles, food particles, and engulfed viruses or bacteria. The membrane surrounding a lysosome prevents the digestive enzymes inside from destroying the cell. Lysosomes fuse with vacuoles and dispense their enzymes into the vacuoles, digesting their contents. They are built in the Golgi apparatus. The name lysosome derives from the Greek words lysis, which means dissolution or destruction, and soma, which means body. They are frequently nicknamed "suicide-bags" or "suicide-sacs" by cell biologists due to their role in autolysis. Lysosomes were discovered by the Belgian cytologist Christian de Duve in 1949.

Acidic environment

At pH 4.8, the interior of the lysosomes is more acidic than the cytosol (pH 7.2). The lysosome single membrane stabilizes the low pH by pumping in protons (H+) from the cytosol via proton pumps and chloride ion channels. The membrane also protects the cytosol, and therefore the rest of the cell, from the degradative enzymes within the lysosome. For this reason, should a lysosome's acid hydrolases leak into the cytosol, their potential to damage the cell will be reduced, because they will not be at their optimum pH!

Enzymes

Some important enzymes in these are: Lysosomal enzymes are synthesized in the cytosol and the endoplasmic reticulum, where they receive a mannose-6-phosphate tag that targets them for the lysosome. Aberrant lysosomal targeting causes inclusion-cell disease, whereby enzymes do not properly reach the lysosome, resulting in accumulation of waste within these organelles.

Functions

The lysosomes are used for the digestion of macromolecules from phagocytosis (ingestion of other dying cells or larger extracellular material), endocytosis (where receptor proteins are recycled from the cell surface), and autophagy (where old or unneeded organelles or proteins, or microbes which have invaded the cytoplasm are delivered to the lysosome). Autophagy may also lead to autophagic cell death, a form of programmed self-destruction, or autolysis, of the cell, which means that the cell is digesting itself.

Other functions include digesting foreign bacteria (or other forms of waste) that invade a cell and helping repair damage to the plasma membrane by serving as a membrane patch, sealing the wound. Lysosomes also do much of the cellular digestion required to digest tails of tadpoles and to remove the web from the fingers of a 3-6 month old fetus. This process of programmed cell death is called apoptosis.[1]

Clinical relevance

There are a number of illnesses that are caused by the malfunction of the lysosomes or one of their digestive proteins, e.g., Tay-Sachs disease, or Pompe's disease. These are caused by a defective or missing digestive protein, which leads to the accumulation of substrates within the cell, impairing metabolism.

Broadly, these can be classified as mucopolysaccharidoses, GM2 gangliosidoses, lipid storage disorders, glycoproteinoses, mucolipidoses, or leukodystrophies.

Structure

Small round structures that contain chemicals.

Additional images


Proteins in different cellular compartments and structures tagged with green fluorescent protein.


External links

References

1. ^ Mader, Sylvia. (2007). Biology 9th ed. McGraw Hill. New York. ISBN 978-0072464634
In cell biology, an organelle is a specialized subunit within a cell, having a specific function, and separately enclosed within its own lipid membrane.

The name organelle
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Digestive enzymes are enzymes in the alimentary tract that break down food so that the organism can absorb it. The main sites of action are the oral cavity, the stomach, the duodenum and the jejunum.
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In biochemistry, a hydrolase is an enzyme that catalyzes the hydrolysis of a chemical bond. For example, an enzyme that catalyzed the following reaction is a hydrolase:

A–B + H2O → A–OH + B–H

Nomenclature


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In cell biology, an organelle is a specialized subunit within a cell, having a specific function, and separately enclosed within its own lipid membrane.

The name organelle
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Bacteria

Phyla

Actinobacteria
Aquificae
Chlamydiae
Bacteroidetes/Chlorobi
Chloroflexi
Chrysiogenetes
Cyanobacteria
Deferribacteres
Deinococcus-Thermus
Dictyoglomi
Fibrobacteres/Acidobacteria
Firmicutes
Fusobacteria
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See also:
A biological membrane or biomembrane is an enclosing or separating tissue which acts as a barrier within or around a cell.
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Digestive enzymes are enzymes in the alimentary tract that break down food so that the organism can absorb it. The main sites of action are the oral cavity, the stomach, the duodenum and the jejunum.
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vacuole (11) cytoplasm (12) lysosome (13) centrioles]] Vacuoles are found in the cytoplasm of most plant cells. Vacuoles are membrane-bound compartments within some eukaryotic cells that can serve a variety of secretory, excretory, and storage functions.
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vacuole (11) cytoplasm (12) lysosome (13) centrioles]] Vacuoles are found in the cytoplasm of most plant cells. Vacuoles are membrane-bound compartments within some eukaryotic cells that can serve a variety of secretory, excretory, and storage functions.
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Autolysis is a process by which a biological cell self-destructs. It is uncommon in adult organisms and usually occurs in injured cells or dying tissue. It occurs when a lysosome allows the digestive enzymes out of its membranes. The cell then, in effect, digests itself.
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Christian René de Duve (born October 2, 1917) is an internationally acclaimed cytologist and biochemist. De Duve was born in Thames-Ditton, Britain, as a son of Belgian emigrants. They returned to Belgium in 1920.
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    pH is a measure of the acidity or alkalinity of a solution. Aqueous solutions at 25 ℃ with a pH less than seven are considered acidic, while those with a pH greater than seven are considered basic (alkaline). The pH of 7.
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    The cytosol (cf. cytoplasm, which also includes the organelles) is the internal fluid of the cell, and a portion of cell metabolism occurs here. Proteins within the cytosol play an important role in signal transduction pathways and glycolysis.
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    Proton

    The quark structure of the proton.
    Composition: 2 up, 1 down
    Family: Fermion
    Group: Quark
    Interaction: Gravity, Electromagnetic, Weak, Strong
    Antiparticle: Antiproton
    Discovered: Ernest Rutherford (1919)
    Symbol: p+
    Mass: 1.
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    proton pump is an integral membrane protein that is capable of moving protons across the membrane of a cell, mitochondrion, or other subcellular compartment.

    Function


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    Ion channels are pore-forming proteins that help to establish and control the small voltage gradient across the plasma membrane of all living cells (see cell potential) by allowing the flow of ions down their electrochemical gradient.
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    Degradative enzyme is an enzyme (in broader sense protein) which degrades biological molecules. Some examples of degradative enzymes:
    • Lipase, which digests lipids,
    • Carbohydrases, which digest carbohydrates (e.g.

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    lipase is a water-soluble enzyme that catalyzes the hydrolysis of ester bonds in water–insoluble, lipid substrates[1]. Lipases thus comprise a subclass of the esterases.
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    Lipids can be broadly defined as any fat-soluble (hydrophobic), naturally-occurring molecules. The term is more-specifically used to refer to fatty-acids and their derivatives (including tri-, di-, and monoglycerides and phospholipids) as well as other fat-soluble sterol-containing
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    A protease is any enzyme that conducts proteolysis, that is, begins protein catabolism by hydrolysis of the peptide bonds that link amino acids together in the polypeptide chain.
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    Proteins are large organic compounds made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid residues.
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    A nuclease is an enzyme capable of cleaving the phosphodiester bonds between the nucleotide subunits of nucleic acids. Older papers may use terms such as "polynucleotidase" or "nucleodepolymerase"[1].
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    A nucleic acid is a macromolecule composed of nucleotide chains. In biochemistry these molecules carry genetic information or form structures within cells. The most common nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
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    A phosphatase is an enzyme that removes a phosphate group from its substrate by hydrolysing phosphoric acid monoesters into a phosphate ion and a molecule with a free hydroxyl group (see dephosphorylation).
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