Lyso = splitting and Soma = body. So, they are concerned with the breaking activities. These are found only in eukaryotic cells.
Structure of Lysosomes
Formation of Primary lysosome
- The enzymes of the lysosomes are synthesized by ribosomes, present on the RER.
- Then they are transferred to Golgi apparatus by RER.
- These enzymes are further processed in the Golgi apparatus.
- They are budded off as Golgi vesicles. These vesicles are called primary lysosomes.
Formation of Secondary Lysosome
Lysosome protect the body against the invading organisms. They also engulf the food particles. The foreign object (germ or food) fuses with the primary lysosomes to form secondary lysosomes. In secondary lysosomes, enzymes digest the food particles.
Sometimes under some abnormal conditions like starvation (3L) or normal physiological conditions, the primary lysosomes engulf the parts of cell. It digests these parts and release energy. The lysosomes which eat parts of its own cells are called autophagosomes. These autophagosomes are also secondary lysosomes.
Functions of Lysosomes
Lysosome performs following function.
Any foreign object which tries to enter into cell is engulfed by lysosome. It is broken into digestible pieces. This process is known as Phagocytosis (cell eating). The animals which show phagocytic activity have most abundant lysosomes. Example: amoeba.
2. Intracellular digestion:
Lysosomes contain enzymes which can digest the phagocytosed food.
3. Extra cellular digestion:
Lysosomes also release enzymes for extra cellular digestion.
Sometimes, lysosomes break parts of their own cells. It is called autophagy. Cell contains some old, broken parts like old mitochondria. They are digested by the lysosomes. In this way, material of the cell is recycled.
5. Degeneration of cells:
The enzymes of cell also cause degeneration of some cells. It may occur during some developmental processes, e.g. Sperms or tail in the development of larva of frog is degenerated.
6. Storage diseases:
Several congenital diseases are caused due to accumulation of certain substances like glycogen and glycolipids. These are called storage diseases. These diseases are produced due to mutation (change in gene). It affects the lysosomal enzymes. These enzymes are involved in the catabolism of above substances. About twenty such diseases are known today. These diseases are caused due to absence of certain enzymes. Examples:
i. Glycogenosis type II:
In this disease, the enzyme which breaks the glycogen into glucose is absent. So glycogen is filled in the membranous bound organelles of the cells of the muscles and liver.
ii. Tay-Sach’s disease:
In this disease, the enzyme which is involved in the catabolism of lipid is absent. It causes accumulation of lipids in brain cells. This disease may cause mental retardation and even death.