- Lysosome word made by Greek Lyso- digestive, soma- body.
- It was discovered by C. De Duve. Alex Novikoff observed It in the cell with an electron microscope and coined the term lysosomes.
- This is a single membrane-bound small vesicular organelle rich in acid hydrolases that breaks all types of biological polymer i.e. proteins, nucleic acids, carbohydrates, and lipids expect cellulose. Acid cellulose are absent in animal
- Found in all cells except prokaryotic cell and mature RBCs.
- These are abundant in phagocyte cells.
- They are less in higher plants.
- Acid hydrolase required an acidic environment for their function that is provided by H+ ATPase. It contains V-type ATPase pumps.
Formation of Lysosome:-
It develops from joint activity of endoplasmic reticulum and Golgi complex.
Type of Lysosomes: –
There are four types: –
- Primary lysosome (Storage Granules):- It is first formed lysosomes which store acid hydrolases in an inactive form. Acid hydroplanes act in acidic medium ( pH~5).
- Secondary Lysosome or Heterophagosome (Digestive Vacuoles):– It is formed by a fusion of primary lysosomes and phagosome or engulfed vesicle. These are called digestive vacuoles. Vesicle contains S-snare protein while lysosome contains T- snare protein. Rab
- Residual body:– lysosome contain undigested material, which may be eliminated by exocytosis. Lipofuscin granule- the residual body may be eliminated from the cell by exocytosis or may be retained within the cytoplasm as a lipofuscin granule.
- Autophagosomes (cytolysosomes):– lysosome, containing cell organelles (e.g. a mitochondrion or portions of the ER) to be digested.
Lysosomal storage disease include:-
- Gaucher’s disease.
- Pompes disease.
- Niteman picks disease.
- Tay-Sachs disease.
Lysosomal stabilizers :
Provide stability to the membrane of the lysosome , which prevents autolysis. E.g. corticosterone, cortisone, cholesterol, antihistamine, heparin, chloroquinone.
Weakened the membrane of lysosome which leads to autolysis. E.g.Vitamin A, D, E,K, progesterone, testosterone, UV radiation, ubiquinone, bile salts, antibiotic digitonin.
Enzymes of Lysosomes:-
it contains following enzymes
1. Heterophagy – digestion of foreign particle through phagocytosis (cell eating) or pinocytosis (cell drinking).
2. Autophagy – digestion of intra-cellular substance.
3. Extracellular digestion – lysosome of bone-eating cell dissolve the undesired part of the bone. E.g. osteoclasts.
4. Autolysis – old cells and infected cells are destroyed by this process. All the lysosomes of cell burst out and digest the cell.
5. Crinophagy – covert inactive hormones into active hormones through lysosome is called crinophagy. E.g. thyroxin.
6. Metamorphosis- during metamorphosis their cathepsin enzyme digest tail of tadpole larva.
7. Mitosis – lysosomes are required to initiate mitosis.
8. Chromosome breaking – DNAase of lysosome can breakup the chromosomes, leads to mutation. Breaking up of 21st chromosomes of man causes blood cancer.
9. Defence – leucocytes, and macrophages of the body are specialized to kill the infecting bacteria.
Note- Ambilysosomes: they show both autophagy and heterophagy