lysosome


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Related to lysosome: primary lysosome

Lysosome

A digestive structure found within virtually all types of animal cells. Lysosome sizes, microscopic appearances, and other properties vary among different cell types and circumstances owing, in part, to differences in their functions and states. Typical lysosomes are roughly spherical or elongate bodies with largest dimensions of 0.1–1 micrometer or greater; tens to hundreds are present in a single cell.

Each lysosome is bounded by a membrane and contains several dozen different species of digestive enzymes, each of which can sever particular chemical bonds found in natural materials. Most lysosomal enzymes function best in an acid environment. This acidification is accomplished by a proton pump, built into the membrane surrounding the lysosome, which effects the transport of hydrogen ions into the lysosomes. See Cell membranes, Enzyme, Ion transport

Lysosomes digest materials taken into the cell from the outside (a process known as heterophagy) as well as other materials that originate in the cell's own cytoplasm (autophagy). The materials to be digested are ultimately incorporated into the same membrane-bounded compartments as the lysosomal enzymes. Selective degradative products can pass out of the lysosome by crossing the membrane, but the enzymes cannot. This sequestration, which protects the cell, persists because the admixture of the enzymes and the materials to digest takes place through fusion of membrane-bounded compartments.

In heterophagy, the cell takes up particles or molecules by the process of endocytosis, engulfing them in membrane-bounded vesicles or vacuoles that are formed at the cell surface. The endocytosed material enters lysosomes via intermediate membrane-bounded compartments known as endosomes. In higher animals, heterophagy is most prominently used by leukocytes and macrophages. These specialized cells endocytose invasive microorganisms and use endocytosis in clearing debris and disposing of dead or senescent cells. See Cell senescence and death, Endocytosis, Phagocytosis

In autophagy, cells segregate regions of their own cytoplasm within compartments that come to be bounded by single membranes and to receive lysosomal enzymes. Autophagic lysosomes take part in the remodeling of cells as part of the processes of development and during stressful circumstances. They also participate, along with nonlysosomal enzymes and heterophagic lysosomes, in normal turnover of the body's constituents—the balanced synthesis and destruction through which most molecules of most cells are replaced by new molecules.

Genetic defects in lysosomal enzymes and related proteins are known to be associated with a large number of rare disorders in humans and animals (such as Tay-Sachs disease and Niemann-Pick disease type C). Defective lysosomal function leads to storage of particular classes of molecules that cannot be degraded and, in long-lived cells such as neurons, to complex pathogenic cascades with widespread impact on endosomal-lysosomal function, membrane trafficking, and signal transduction. Such disorders are most often fatal. Lysosomes or prelysosomal structures also have been “adopted” as intracellular homes by certain pathogenic microorganisms that avoid or survive the attacks of the lysosomal system. Some strains of viruses, and toxins such as the one responsible for diphtheria, may use endosomes as their route of entry into the cell, penetrating through the endosomal membrane into the surrounding cytoplasm.

lysosome

[′lī·sə‚sōm]
(cell and molecular biology)
A specialized cell organelle surrounded by a single membrane and containing a mixture of hydrolytic (digestive) enzymes.
References in periodicals archive ?
'We then found an older study, from 2004, which showed that the fusion between phagosomes and lysosomes is blocked by these two enzymes.
Julian's collaborative team of researchers in the Department of Chemistry and the Division of Biomedical Sciences at UC Riverside posits that long-lived proteins can undergo spontaneous modifications that can make them undigestible by the lysosomes.
Cobalt protoporphyrin accelerates TFEB activation and lysosome reformation during LPS-induced septic insults in the rat heart.
While CD28 resides mainly on the cell surface, CTLA-4 is located first in intracellular compartments such as Golgi apparatus, endosomes, secretory granules and lysosomes. The T cell receptor (TCR) stimulation promotes CTLA-4 trafficking from vesicular compartments to the cell membrane, however, once it is already in the membrane, this receptor is continuously endocytosed via clathrin-coated vesicles.
'The lysosome is isolated in the cell because it's so toxic.
Restoring the ability of the lysosomes to function normally rejuvenates the cells' ability to activate, the researchers at the Stanford University School of Medicine found.
SLC15A4 regulates the amino acid composition of lysosome as well as the acidity of lysosome, consequently affecting protease cleavage of TLR7 and TLR9 in lysosomes.
To determine the percentage of bacteria that colocalized with the lysosome marker 100 intracellular bacteria were counted.
(1994) Lysosome biogenesis requires Rab9 function and receptor recycling from endosomes to the trans-Golgi network.
Lysosome pathway was the significantly enriched pathways enriched by intersection genes.
Repair Effect of Polysaccharides on Lysosome. Acridine orange (AO) is a weak base that can go into the lysosome through the cell membrane.
Yeast cells have a structure similar to lysosomes called 'vacuoles'.