Lysosome Structure Function and Types

LYSOSOME:

  • 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: –

  1.  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).
  2. 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
  3. 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.
  4. Autophagosomes (cytolysosomes):– lysosome, containing cell organelles (e.g. a mitochondrion or portions of the ER) to be digested.

Lysosomal storage disease include:-

  1. Gaucher’s disease.
  2. Pompes disease.
  3. Niteman picks disease.
  4. Tay-Sachs disease.

Picture

Source- Karp

Lysosomal stabilizers :

Provide stability to the membrane of the lysosome , which prevents autolysis. E.g. corticosterone, cortisone, cholesterol, antihistamine, heparin, chloroquinone.

Lysosomal labilizer:-

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
Picture


Source- Sheeler and Bianchi
Picture

source- Karp

Functions:-
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
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