Pleomorphism of Lysosomes

 Pleomorphism of Lysosomes

Lysosomes show pleomorphism, which means they occur in many different forms according to their functional state. They are not always identical in shape, size, or contents. Their appearance changes depending on whether they are newly formed, involved in digestion, or storing undigested waste materials. Lysosomes are membrane-bound organelles containing hydrolytic enzymes. These enzymes digest proteins, lipids, carbohydrates, nucleic acids, and other cellular materials. Since lysosomes perform different digestive functions inside the cell, they appear in different structural forms. This property is called pleomorphism. The main pleomorphic forms of lysosomes are primary lysosomes, secondary lysosomes, autophagic vacuoles, and residual bodies.

Primary lysosomes are newly formed lysosomes produced by the Golgi apparatus. They contain inactive hydrolytic enzymes and have not yet taken part in digestion. They are small, spherical vesicles surrounded by a single membrane.

Secondary lysosomes are formed when primary lysosomes fuse with food vacuoles or phagosomes. In these lysosomes, digestion takes place. Their contents are heterogeneous because they contain both digestive enzymes and the material being digested. Secondary lysosomes are also called digestive vacuoles.

Autophagic vacuoles are formed when lysosomes digest old, damaged, or worn-out cell organelles. This process is called autophagy. For example, damaged mitochondria or endoplasmic reticulum may be enclosed in a membrane and then fused with lysosomes for digestion. Autophagic vacuoles help in recycling cellular components.

Residual bodies are lysosomes that contain undigested or indigestible waste materials after digestion is complete. These waste materials may remain in the cell for some time or may be removed by exocytosis. In some long-lived cells, residual bodies may accumulate as ageing pigments such as lipofuscin.