Lysosomes

Lysosomes are electron microscopic vesicular or sac-like structure of cytoplasm that is involved in intracellular digestive activities. They are commonly called as suicidal bags. They are absent in prokaryotic cells but are present in an animal cell except R.B.C. They occur in large number in those cells which carry out a phagocytic activity like W.B.C. The plant lysosomes are called spharosomes.

Structure of lysosomes

Lysosomes are mostly rounded or spherical in shape and sometimes irregular. The size of the lysosome is variable and it ranges from 0.2 to 0.8µm. Lysosomes consist of a lipoproteinous membrane which encloses a fluid called a matrix. The matrix contains different types of hydrolytic or digestive enzymes. Eg; Nucleases, proteases, glycosidases.

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fig:Structure of lysosomes

Types of lysosomes

Lysosomes are called polymorphic cell organelles because they exist in different forms inside the same cell. On the basis of nature of matrix lysosomes are categorized into four types;

• Primary lysosome
• Secondary lysosome
• Tertiary lysosome
• Autophagosomes

Primary lysosome

It is newly formed lysosome which contains only inactive enzymes.

Secondary lysosome

It is formed by the fusion of primary lysosome with food carrying phagosome and pinosome. It contains food and active enzymes and the digestion occurs inside it.Hence, it is also called digestive vacuole.

Tertiary lysosome

It is also called residual bodies containing waste material and undigested food which are thrown out of the cell by exocytosis.

Autophagosome

It is formed when there is a scarcity of foreign or outside food. In this condition, primary lysosome digests reserved food or cell organelles.

Functions of lysosomes

• It helps in heterophagy which involves the digestion of foreign food taken inside through endocytosis.
• It also carries out digestion of reserved food or cell organelles during the scarcity of foreign food.
• It carries out autolysis in which enzymes of lysosomes are released outside their membrane and digest the entire cell or even tissue. Eg; Disappearance of tadpole tail during metamorphosis into a frog.
• Due to self-destructive activity like autolysis, lysosomes are called suicidal bags.
• It helps in extracellular digestion. Eg; fungi
• It provides a natural defence to our body through cells like WBC.
• lysosomes act as scavenger and help in removing dead or old cells.