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 ?
In 1955, he collaborated with Christian de Duve on lysosomes.
Observed increases in the numbers of lysosomes suggest further cellular degradation.
Lysosomes have been defined as intracellular digestive organelles that are generally assumed to have an internal pH of 4.
In contrast, MDMs treated with C/Fe particulates exhibited coalescence of particulate-containing lysosomes.
One of the receptor molecules transporting lysosome components is the mannose-6-phosphate receptor (M6P receptor) (see figure 2), which recognizes and binds proteinase precursors during their transit to the lysosome.
It has been reported that lysosome hydrolase activity levels are enhanced in the hippocampus with the onset of early-stage Alzheimer's disease and that lysosomal vacuole quantities are increased in several protein-deposition disorders [28].
46) In 2007 she established that age-related autophagy decline is primarily due to changes in the lysosome membrane.
This enzyme is necessary for appropriate mannose 6-phosphate tagging, the phosphorylation of mannoses in oligosaccharide side chains that marks lysosomal hydrolases for uptake into the lysosome.
Objective: For a long time the lysosome has been viewed as a static organelle that performs routine work for the cell, mostly pertaining to degradation and recycling of cellular waste.
mRFP is more stable than GFP in the acidic/proteolytic environment of the lysosome.
Thirty-one contributions are then organized according to their relevance across the progression from plasma membrane to lysosome.