Lysosome: Definition, Function, and Examples

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Lysosome Definition

Lysosome in an organelle that includes a variety of digestive enzymes that are used to break down excess or worn-out organelles, food particles, and ingested viruses or bacteria.

What is Lysosome?

The word “organelle” literally means “tiny organs.” The cell, like the rest of the body, is made up of a variety of organs that perform particular functions. The definition of an organelle in some texts is rather specific.

A structure enclosed by two lipid bilayers is known as an organelle. Because their membranes are made up of two lipid bilayers, the nucleus, endoplasmic reticulum, Golgi apparatus, mitochondria, and chloroplast (plastid) are considered organelles, but ribosomes and nucleosomes are not.

Similarly, because they are single-membrane-bounded cytoplasmic structures, lysosomes and vacuoles do not qualify as organelles. Other sources, on the other hand, have less limitations.

An organelle is a specialised component of a cell that serves a specific purpose. There are two sorts of organelles in this case: Organelles that seem to be membrane-bound (including both double- and single-membraned cytoplasmic structures) and organelles that are not membrane-bound.

Membrane-bound organelles have included nucleus, endoplasmic reticulum, Golgi apparatus, mitochondria, plastids, lysosomes, and vacuoles.

Non-membrane-bound organelles, ribosomes, and ribs encompass ribosomes, spliceosomes, vaults, proteasomes, DNA polymerase III holoenzyme, RNA polymerase II holoenzyme, photosystem I, ATP synthase, nucleosomes, centrioles, microtubule-organizing centres, cytoskeleton, flagellum, nucleolus.

Lysosome Characteristics

Christian de Duve, a Belgian cytologist, discovered lysosomes in 1949. Lysosomes are spherical vesicles that contain a variety of digesting enzymes (hydrolytic). The rough endoplasmic reticulum synthesises these digesting enzymes, which are lysosomal enzymes.

They are then subjected to post-translational changes in the Golgi apparatus, which include the addition of mannose 6-phosphate as a label. Finally, via branching out from the Golgi apparatus, they are imported as vesicles.

The vesicles’ enzymes will largely be utilised to breakdown and remove superfluous or worn-out organelles, food particles, and absorbed viruses or bacteria. The pH of the lysosome lumen ranges from 4.5 to 5.0, which is ideal for the hydrolysis enzymes.

Protons (H+ ions) from the cytosol are pumped into the lysosome through proton pumps and chloride ion channels, allowing it to maintain this ideal pH. Lysosomes are part of the GERL system, which comprises the Golgi apparatus and the endoplasmic reticulum in addition to lysosomes. Endocytosis and exocytosis are two biological processes linked to the GERL system.

Types of Lysosome

According to their developmental phases, there are two types of lysosomes: (1) primary lysosomes and (2) secondary lysosomes. The primary lysosome is a newly created lysosome that has not yet been exposed to the digested material. It is now known as a secondary lysosome when it merges with a vacuole holding the substance.

Biological Function of Lysosome

Lysosomes are involved in the digestion of macromolecules derived from phagocytosis, endocytosis, and autophagy, as well as the digestion of bacteria and other waste products. As a result, the lysosomes serve as the cell’s waste disposal mechanism.

Apart from that, they also play a role in apoptosis and the healing of damage to the plasma membrane by functioning as a membrane patch (e.g. digesting web from a Three to 6-month-old foetus’ fingers).

Because of their involvement in autolysis, they are sometimes referred to as “suicide-bags.” Cell signalling and energy metabolism are two of its other roles.

Lysosome and Intercellular Digestion

Hydrolytic enzymes in the membrane and lumen of lysosomes accelerate the digestion of materials. The first stage is endocytosis, in which the substance enters the cell as a food vacuole via the cell membrane. The lysosome then merges with the food vacuole, releasing the food vacuole’s hydrolytic enzymes.

Finally, the hydrolytic enzymes breakdown the contents. The vesicle then contracts, resulting in tiny membrane-bound vesicles. The remains of digested elements are referred to as residual bodies.

Lysosome, Genetics, and Pathology

The genes in the nucleus code for lysosomal enzymes. Because mutations in these genes might result in malfunctioning lysosomal enzymes, they may cause genetic diseases. Metabolic problems may result if this happens.

Certain materials (metabolites, waste materials, etc.) tend to collect in the absence of a working lysosomal enzyme, which might disrupt regular, correct metabolism. The fundamental aetiology of Tay-Sachs disease is this.

Tay-Sachs disease is a neurological disorder that causes neurodegeneration, developmental disabilities, and sometimes death. It is caused by a lack of a functioning hexosaminidase enzyme.

GM2 gangliosides accumulate in neurons as a result of this. Other metabolic problems brought about by a change bringing about broken or an insufficiency of utilitarian lysosomal catalysts are Farber illness, Krabbe sickness, galactosialidosis, gangliosides, alpha-galactosidase (for example Fabry illness, Schindler infection, and so on), beta-galactosidase, GM2 gangliosidosis (for example Sandhoff illness, Tay-Sachs infection, and so on), glucocerebroside (for example Gaucher illness), sphingomyelinase (for example lysosomal corrosive lipase inadequacy), sulfatidosis, mucopolysaccharidosis, mucolipidosis, lipidosis (for example neuronal ceroid lipofuscinosis, Wolman illness, and so on), cholesterol ester stockpiling sickness, lysosomal transport infection, glycogen stockpiling illness, and so on. Lysosomal storage disease is the general concept for several conditions.

Lysosome Citations
  • Autophagosome-Lysosome Fusion. J Mol Biol . 2020 Apr 3;432(8):2462-2482.
  • Lysosome: The metabolic signaling hub. Traffic . 2019 Jan;20(1):27-38.
  • The Lysosome as a Regulatory Hub. Annu Rev Cell Dev Biol . 2016 Oct 6;32:223-253.
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