Lysosomes: Definition, Discovery, Structure, Function and Related Diseases

Table of Contents

  • Introduction

  • Definition and Characteristics of Lysosome

  • Discovery and Structure

  • Isolation and Discovery by De Duve (1949)
  • Unique Morphology and Single Membrane

  • Enzymatic Content

  • Overview of Hydrolases
  • Phagocytosis: Lysosomes' Role in Digesting Foreign Objects
  • Abundance in Phagocytic Animal Cells (e.g., Neutrophils)

  • Synthesis and Processing

  • Enzyme Synthesis on the Rough Endoplasmic Reticulum (RER)
  • Processing in the Golgi Apparatus
  • Formation of Primary Lysosomes

  • Autophagy

  • Explanation of Autophagy (Self-Eating)
  • Role in Recycling and Renewal of Cellular Materials
  • Potential Consequences for Cellular Degeneration

  • Malfunctioning of Lysosomes

  • Overview of Storage Diseases

  •  Example: Glycogenosis Type II
  •  Example: Tay-Sach's Disease and Lipid Accumulation

Lysosomes: Definition, Discovery, Structure, Function and Related Diseases


Lysosomes

Lysosomes (lyso -splitting; soma–body) are cytoplasmic organelles found
in most eukaryotes and are different from others cytoplasmic organelles due to their morphology.

Discovery 

Lysosomes were isolated as separate first time by De Duve in 1949.

Structure and Function of Lysosome 

They are surrounded by a single membrane and are simple sacs that contain very large variety of food digesting enzymes called hydrolases. Any foreign objects that gain entry with in the cell are immediately engulfed by the lysosomes and are completely broken down into digestible pieces. This process is known as phagocytosis. They are very abundant in those animal cells which exhibit phagocyticactivity 
e.g neutrophils.

Synthesis of Lysosome 

Lysosomes are bounded by single membrane and contain numerous
hydrolytic and acid phosphatase enzymes. These enzymes are synthesized on RER and are further processed in the Golgi apparatus. The processed enzymes are budded
off as Golgi vesicles and are called primary lysosomes. 

Lysosomes Enzymes 

Lysosomes contain those enzymes which can digest the phagocytosed food particles. During autophagy (self
eating) some old worn outparts
of the cell are also digested. In
this way, materials of cell may be recycled and cell may be renewed. Their enzymes can also result in degeneration of
cell, as may occur during the 
developmental processes.

Storage Diseases Related to Lysosomes 

Several congenital diseases have been found to be due to accumulation ofsubstances such aslglycogen or various lipids within the cell. These are also called storage diseases and are produced by a mutation that affects one of the lysosomal enzymes involved in the catabolism of certain substances.

For example, in glycogenosis type II disease, the liver and muscles cells appear filled with glycogen with in membrane bound organelles. In this disease, an enzyme that converts glycogen to glucose, is absent. Similarly Tay-Sach's disease is involved in the catabolism of lipids. Accumulation of lipids in brain cells lead to mental retardation and even death.

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