Secondary lysosome

Biological terminology

This entry is made by Compilation and application of scientific encyclopedia entries of "Science Popularization China" to examine.

This kind of lysosome contains hydrolase and corresponding substrate, which is a kind of lysosome that will or is undergoing digestion. According to the source of the digested material, it can be divided into Autophagic lysosome 、 Heterophagy lysosome 。

Secondary lysosomes are hydrolytic enzymes and corresponding substrates, as well as hydrolytic digestion products, that is, vesicles that are undergoing or have undergone digestion. Therefore, the secondary lysosomes are also called active lysosomes or digestive vacuoles. It is widely distributed and diversified in form.

Chinese name: Secondary lysosome
Foreign name: secondary lysosome
Alias: Active lysosome 、 Digestive vesicle

Applied discipline: Human Histology Cell
Main categories: Heterologous lysosome
Features: Wide distribution and diverse forms

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brief introduction

function of lysosome

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The lysosome has two functions:

First, the relationship between Food bubble Fusion devour The food or pathogenic bacteria and other large particles are digested into biological macromolecules, and the residues are discharged from cells through efflux;

Second, in cell differentiation In the process, some senescent organelles and biological macromolecules fall into lysosomes and are digested, which is the need for the organism to reorganize itself. A spherical organelle located in the cytoplasm and surrounded by unit membranes.^[1]

morphological structure

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Its size varies with cell type, with a diameter of 0.2 to several microns. More than 50 kinds of acid hydrolases (such as lipase, proteolytic enzyme, sulfatase, etc.) are known in lysosomes. It widely exists in the cells of animals and protozoa, plant cell There are lysosomal like organelles in the. Lysosomes are generally divided into primary lysosomes and secondary lysosomes. It is generally believed that lysosomal enzymes are synthesized in rough endoplasmic reticulum, transported to Golgi apparatus, processed and packaged Flat capsule The secretory surface (also known as the reverse surface and the mature surface) sprouts and falls off, forming vesicles containing lysosomal enzymes (i.e. primary lysosomes), and fuses with the endosomes or phagocytes to form secondary lysosomes (also known as digestive vesicles) for digestion. Another insight has been put forward, that is, the concept of primary and secondary lysosomes is not given, and the lysosomal precursor is called endolysosome.^[1]

classification

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The substance has begun to digest in it, but the main digestion process is in the lysosome. According to the source of lysosomal agents, the secondary lysosomes are divided into:

(1) Heterologous lysosome (het - erolysosome), refers to the Macromolecular solution Or viruses, bacteria, etc., the former forms pinocytosis vesicles (or endosomes) through pinocytosis (including receptor mediated endocytosis), and the latter forms phagocytosis vesicles through phagocytosis, which fuse with primary lysosomes (or endosomes) to form secondary lysosomes (or lysosomes) respectively.

(2) Autolysosome or autophagy lysosome refers to the secondary lysosome formed by the fusion of autophagosome and primary lysosome (or endolysosome) that surrounds some damaged or aging organelles (mitochondria, endoplasmic reticulum fragments, etc.). The substances digested are endogenous. The secondary lysosomes containing undigested residues are called residual bodies. Some residual substances can be discharged, and some can be stored in cells for a long time without being discharged. Lysosomes in Intracellular digestion It plays a key role in the metabolism of normal cells. Digested nutrients such as amino acids, sugars, etc. enter the cytoplasm through the lysosomal membrane and are absorbed and utilized. In addition, it can digest and decompose bacteria and pathogens through foreign phagocytosis, so it has a defensive function; adopt Autophagy , use their own substances as nutrition, cope with external adverse conditions, and avoid their own permanent casualties; Through autolysis, degenerated cells, organs and dead cells in the development process can be eliminated to ensure the normal growth and development of cells. Sperm acrosome is a specialized lysosome, which removes the outer coating and attachment of egg cells by releasing internal digestive enzymes Follicular cell The egg cell fuses with the sperm plasma membrane to make the sperm enter the egg cell and complete fertilization. More than 40 diseases are known to be related to the lack of certain enzymes in lysosomes, such as congenital storage diseases; Another example is the formation of silicosis Rheumatoid arthritis It is related to lysosomal membrane damage and lysosomal enzyme release.^[1]

Lysosomal lesion

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1. Pathological storage process of lysosomes Under certain pathological conditions, some endogenous or exogenous substances can be stored in the lysosome to increase the number of diseased enzymes. The substances stored in lysosomes are degraded (digested) by lysosomal enzymes. But sometimes the amount of material entering the cell is too much, which exceeds the processing capacity of lysosome, so it is stored in the cell. For example, proteinuria caused by various reasons can be found in the proximal convoluted tubule of the kidney epithelial cells The storage of glassy drop like protein (so-called glassy drop denaturation) is seen in. Under the electron microscope, it can be seen that this glass like droplet is an enlarged lysosome containing protein, so in essence, it is often a manifestation of enhanced cell function, which is different from true denaturation. Some substances that can be digested under normal conditions, such as glycogen and mucopolysaccharide, can also be accumulated in the lysosome when the lysosome has congenital enzyme defects, such as type II Glycogen storage disease (Pompe) disease.

2. The role of lysosomes in the process of cell autolysis Lysosomes play an important role in the process of cell autolysis because they contain many kinds of hydrolases. When lysosome membrane is damaged and permeability is increased, hydrolase escapes, causing extensive cell autolysis. This is in vivo Cell necrosis And autolysis after death. In this process, the macromolecular components of damaged cells are decomposed into small molecules by hydrolase. More important than the extensive necrosis or autolysis of cells is the role of lysosomes in the focal necrosis of cells. At this time, autophagic vesicles are formed in the cytoplasm, and they combine with lysosomes to form autophagic lysosomes. If the hydrolase cannot completely digest and dissolve the structure, autophagic lysosomes are often transformed into residual bodies in cells, such as lipofuscin 3 in some long-lived cells Intercellular substance Role in injury When lysosomal enzymes are released into the cytoplasm, they also play their role in enzymatic destruction. This is in all Rheumatoid arthritis It plays an important role in the process of inflammation and invasion of tumor cells into blood vessels. However, the mechanism of lysosomal enzymes escaping from lysosomes into the intercellular space is not very clear, which may be due to the instability of lysosomal membrane and cells or through the process of exocytosis. Therefore, lysosomal membrane stabilizers can be used clinically to treat related diseases.^[1]

Related information

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Lysosomes are generally divided into Primary lysosome And secondary lysosomes. The primary lysosome originates from Golgi apparatus, or the specialized region of smooth endoplasmic reticulum near the secretory surface of Golgi apparatus, and only hydrolase is contained in the capsule. The secondary lysosome is formed by the fusion of the primary lysosome with the small vesicles formed by phagocytosis or pinocytosis, or with the membrane and other structures after organelle damage. The residue of secondary lysosome after enzymolysis is called residue or Terminal lysosome , i.e optical microscope The lipofuscin seen below (see figure).

Formation and function of lysosomes in allophagocytosis and autophagy of cells

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