Lysosomes - Suicidal Bags

Lysosomes are another organelle which is mostly found in animal cells; very rarely in plant cells. It is also called 'suicidal bags' because they are responsible for digestion of cell's bio-molecules, old cell parts and micro-organisms.

Structure:

Structure of Lysosome

Lysosomes are sac-like organelles which are bound by a membrane. The lysosomes arise from Golgi apparatus by budding off from its membrane. The interior of lysosomes is acidic is nature with pH around 4-4.5. This acidic environment is maintained in the interior by proton pumps. The interior contains a variety of enzymes (acid hydrolases). These hydrolytic enzymes degrade proteins, nucleic acids, carbohydrates and lipids. These enzymes cannot work outside the lysosomes as the pH of the cell is slightly alkaline or neutral. So, if there is lysosomal rupture or leakage, this acid-dependent activity protects the cell from self-degradation.

Functions:

Diagramtic Representation of Process of Degradation by Lysosomes

The main function is the break down and removing of old parts of the cell or microorganism. The lysosomes fuses with membrane bound vesicle that arises from any of these pathways - endocytosis, phagocytosis or autophagocytosis. These vesicles are referred to as endosomes, phagosomes and autophagosomes respectively. These endosomes fuses with lysosomes (primary lysosomes) and forms secondary lysosomes (sometimes referred to as endolysosomes). The bio-molecules are further broken down into smaller forms like amino acids, monosaccharides, nucleotides and fatty acids which are then recycled in the cell.