For cell biology students

1. Lysosomes
Dr. Gauri Haval
A.G. College,
Pune

3. • Lysosomes are tiny membrane bound vesicles
• Involved in intracellular digestion
• Contain variety of hydrolytic enzymes
• They break down excess or worn-out cell parts.
• They may be used to destroy invading viruses and
bacteria.
• Capable of degrading proteins, lipids, and
carbohydrates.
• Involved in nutrient sensing and storage and
retrieval.
• Highly dynamic and are capable of fusion and
fission events with other organelles and plasma
membrane.

4. • Lysosomes occur in
• Most plant and animal cells
• Absent in bacteria, mammalian erythrocytes
• Present in Leukocytes especially granulocytes
are rich source of lysosomes. In these cells
they are large.
• Lysosomes are numerous in epithelial cells of
absorptive, secretory and excretory organs, in
lungs, uterus, phagocytic cells of bone
marrow, spleen and liver.

5. Origin of Lysosomes

6. Structure
• Lysosomes are round membrane bound
vesicles, filled with dense material
• Shape and density vary greatley
• Difficult to identify
• Three criteria are used to identify Lysosomes
1) It should be bounded by limiting membrane
2) It should contain two or three acid hydrolases
3) It should show the property of membrane
latency (latency is the proportion of lysosomal
membranes that maintain their integrity)

7. Lysosomal enzymes
• About 40 enzymes
• Include- proteases, nucleases, glycosidases,
lipases, phospholipases, phosphatases,
sulfatases.
• All are acid hydrolases. They are optimally active
at an acidic pH near 5
• The lumen of lysosomes is maintained at acidic
pH by a H+ pump. This is active transport by using
ATP.
• Even if these enzymes leak out in cytoplasm, they
do not damage the contents because the pH of
cytoplasm is 7.2

8. Lysosomal Membrane
• It contains transport proteins that allow the
final products of digestion of macromolecules
to escape.
• These products can be either excreted or
utilized by the cell.
• Membrane also contains H+ pump
• Most of the lysosomal membrane proteins are
highly glycosylated. This glycosylation protects
these proteins from lysosomal proteases in
the lumen

9. Polymorphism in Lysosomes: 4 types of lysosomes

10. • These four types of lysosomes have been
recognized in different types of cells or at
different times in the same cell.
1. Primary lysosomes-
2. Heterophagosome
3. Autophagosome
4. Residual bodies