Lysosomes: Meaning, Structure and Function (With Diagram)

In this article we will discuss about:- 1. Meaning of Lysosomes in Cell 2. Structure of Lysosomes in Cell 3. Function.

Meaning of Lysosomes in Cell:

Lysosomes are ultra structural particles of the cell containing hydrolytic enzymes responsible for digestion. Though these are common in ani­mal cell, but in plants these are found in the lower groups, such as euglenoids, slime moulds and some saprophytic fungi.

Particles isolated from tobacco and maize seedlings contain seve­ral of the hydrolases found in animal lysosomes. They are so called because they contain lytic or destructive enzymes. The enzymes, if released, can digest the cell and hence lysosomes are sometimes called ‘suicide bags’.

Structure of Lysosomes in Cell:

Lysosomes are globular or granu­lar in appearance of 0.2-0.5µm size without any characteristic shape or structure. These are bounded by a single lipoprotein membrane con­taining enzymes in crystalline form. The enzymes present are phosphatase, nuclease, lipase, protease, glycosidase, sulfates, amylase.

The membrane is impermeable to substrates of the enzymes contained in the lysosome. Certain substances, called labializes, cause instability of the lysosomal membrane, leading to release of enzymes from the lysosome. Other substances, called stabilizers, have a stabilizing action on the membrane. This prevents uncontrolled digestion of the cell contents and thus protects the cell from autolysis.

The lysosomes show polymorphism in diffe­rent cell types. There are two basic types of lyso­somes. Golgi complex buds off primary lysosomes containing hydrolytic enzymes. The vacu­ole or phagosome arising by endocytosis asso­ciates and fuses with primary lysosome to form secondary lysosome (Fig. 2.61).

Incomplete digestion results in residual bodies. Lysosomes sometimes include intracellular part like mito­chondria or endoplasmic reticulum for digestion are called auto-phagosome.

Function of Lysosomes in Cell:

Lysosomes are bags containing digestive enzymes involved in digestion of intra­cellular and extracellular particles. The primary lysosomes secrete hydrolases outside by exocytosis, resulting in degradation of the extracellu­lar material (extracellular digestion). Saprophytic fungi utilize extracellular digestion for nutrition.

Digestion of substances within the cell is called intracellular digestion. Intracellular digestion may involve heterophagy or autophagy. Heterophagy is the intake of exogenous material into the cell by endocytosis and the subsequent breakdown of this material by enzymes in secon­dary lysosomes. Autophagy brings about diges­tion of cell’s own material on the death of a cell, or with cellular injury.