Lysosome

These are membrane bound vesicular structures formed by the process of packaging in the golgi apparatus

The isolated lysosomal vesicles have been found to be very rich in almost all types of hydrolytic enzymes hydrolases - lipases, proteases, carbohydrases) optimally active at the acidic pH (pH=5). These enzymes. capable of digesting carbohydrates, proteins, lipids and nucleic acids.

fig : Lysosome

With the exception of mammalian RBC they were reported in all animal cells.

In plant cells large central vacuole functions as Lysosome. So in higher plants lysosomes are less frequent. But number of lysosomes is high in fungi (bcz their mode is absorpton). 

• Periplasmic Space - space between cell wall and cell membrane in bacteria.may play similar role.
• Lysosomes are spherical bag like structures, which is covered by single unit membrane. They are large sized in Phagocytes (WBC).
• Lysosomes are filled with 50 different type of digestive enzymes termed as Acid hydrolases digestion of all type of macromolecules.
• These acid hydrolases function in acidic medium (pH=5). Membrane of lysosome has an active H pump mechanism which produce acidic pH in lumen of lysosome.
• "Lysosomes are highly polymorphic.cell organelle. Because, lysosomes have different physiological states.

TYPES OF LYSOSOMES

1. Primary Lysosomes or storage granules. These lysosomes store enzyme Acid Hydrolases in the inactive form. (Enzymes synthesized on ribosomes in cytoplasm) these are newly formed lysosome
2. Digestive vacuoles or Heterophagosome - These lysosome formed by the fusion of primary lysosomes and phagosomes. These are secondary Lysosomes
3. Residual bodies :- Lysosomes containing undigested material are called residual bodies. These may be eliminated by exocytosis
4. Autophagic Lysosomes or autophagosomes :- Lysosomes containing cell organelles to be digested are known as Autophagosomes.

FUNCTIONS

(1) Intracellular digestion :-

a) Heterophagy :- This is digestion of foreign materials received in cell by phagocytosis and pinocytosis:

b) Autophagy :- Digestion of old or dead cell organelles. Autophagy also takes place during starvation of cell.

(2) Extracellular digestion :

Lysosomes of osteoclast (bone eating cells) dissolve unwanted part of bones.

(Extracellular digestion also occurs by fungal lysosomes)

(3) Cellular digestion (Autolysis) - Sometimes all lysosomes of a cell burst to dissolve the cell completely. (so Lysosome caled as suicidal bags of cell).

   Old cells are removed by autolysis. unwanted organs of embryo are destroyed by autolysis Cathepsin of lysosome digests the tail of tadpole of frog during metamorphosis.