Lyso = splitting and Soma = body. So, they are concerned with breaking activities. These are found only in eukaryotic cells.
Structure of Lysosomes
They are bounded by a single membrane. This membrane forms a simple sac. This sac contains several hydrolytic enzymes like acid phosphatase.
Formation of Primary lysosome
- The enzymes of the lysosomes are synthesized by ribosomes, present on the RER.
- Then they are transferred to the 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 protects the body against invading organisms. They also engulf 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 the cell. It digests these parts and releases energy. The lysosomes which eat parts of its own cells are called autophagosomes. These autophagosomes are also secondary lysosomes.
Functions of Lysosomes
Lysosome performs the following function.
Any foreign object which tries to enter the cell is engulfed by the lysosome. It is broken into digestible pieces. This process is known as phagocytosis (cell eating). The animals which show phagocytic activity have the most abundant lysosomes. Example: amoeba.
2. Intracellular digestion:
Lysosomes contain enzymes that can digest phagocytosed food.
3. Extracellular digestion:
Lysosomes also release enzymes for extracellular digestion.
Sometimes, lysosomes break parts of their own cells. It is called autophagy. The cell contains some old, broken parts like old mitochondria. They are digested by the lysosomes. In this way, the material of the cell is recycled.
5. Degeneration of cells:
The enzymes of cells also cause degeneration of some cells. It may occur during some developmental processes, e.g. Sperm or tail in the development of larva of frog has degenerated.
6. Storage diseases:
Several congenital diseases are caused due to the accumulation of certain substances like glycogen and glycolipids. These are called storage diseases. These diseases are produced due to mutation (change in a gene). It affects lysosomal enzymes. These enzymes are involved in the catabolism of the above substances. About twenty such diseases are known today. These diseases are caused due to the 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-Sachs disease:
In this disease, the enzyme which is involved in the catabolism of lipids is absent. It causes the accumulation of lipids in brain cells. This disease may cause mental retardation and even death.