Lysosomes
Introduction
The word ‘Lysosome’ has been derived from two words i.e.
- ‘Lyso’ means splitting.
- ‘Soma’ means body.
These were isolated as separate components for the first time by De Duve (1949).
These are mostly found in eukaryotic cells and are most abundant in these animal cells which exhibit phagocytosis.
Structure
They are bound by a single membrane and are simple sacs rich in acid phosphates and several other hydrolyticenzymes. These enzymes are synthesized on RER and are further processed in the Golgi apparatus. The processed enzymes are budded off as Golgi vesicles and are called as primary lysosomes
Functions
(i) Phagocytosis
Lysosomes contain those enzymes which can digest the phagocytosed food. Any foreign object that gains entry into the cell is completely broken into simple digestible pieces. This process is known as phagocytosis (eating process of cell). They also contain enzymes, which can digest the phagocytosed food particles.
(ii) Autophagy
They are also involved in autophagy (self eating). During this process, some old, worn out parts of cell, such as old mitochondria are digested. In this way, materials of cell may be recycled and cell may be renewed.
(iii) Degeneration
Their enzymes can also result in degeneration of cell, as may occur during some developmental processes.
(iv) Extracellular Digestion
They also release enzymes for extra cellular digestion.
DISEASES RELATED TO LYSOSOMES
Several congenital diseases have been found to be due to accumulation within the cell of substance such as glycogen or various glycolipids. These are also called storage diseases and are produced by a mutation that affects one of the lysosomal enzymes involved in the catabolism of a certain substance.
Examples
- About twenty such diseases are known these days, which are because of absence of a particular enzyme.
- In glycogenosis type II disease, the liver and muscles appear filled with glycogen within membrane-bounded organelles. In this disease, an enzyme that degrades glycogen into glucose is absent.
- Tay-Sach’s disease is because of absence of an enzyme that is involved in the catabolism of lipids. Accumulation of lipids in brain cells lead to mental retardation and even death.
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