Lysosomes: History, Formation, Function, Action and Disorders of Lysosomal Function

It is a subcellular organelle that is found in almost all types of eukaryotic cells.

Each lysosome is surrounded by a membrane that maintains an acidic environment inside through a proton pump. Lysosomes contain a wide variety of hydrolytic enzymes (acid hydrolases) that break down macromolecules such as nucleic acids, proteins, and polysaccharides.

These enzymes are active only in the acidic interior of the lysosome; its acid-dependent activity protects the cell from autodegradation in the event of lysosomal leakage or breakdown, since the cell’s pH is neutral to slightly alkaline.

History

Lysosomes were discovered by the Belgian cytologist Christian René de Duve in the 1950s. This discovery was awarded the Nobel Prize in Physiology or Medicine in 1974.

Formation of lysosomes

Lysosomes originate by sprouting from the membrane of the trans-Golgi network, a region of the Golgi complex responsible for classifying newly synthesized proteins, which can be designated for use in lysosomes, endosomes, or the plasma membrane.

The lysosomes then fuse with membrane vesicles that are derived in one of three ways: endocytosis, autophagocytosis, and phagocytosis.

A lysosome is basically a specialized vesicle that contains a variety of enzymes. The enzyme proteins are first created in the rough endoplasmic reticulum.

Those proteins are packed into a vesicle and sent to the Golgi apparatus. The Golgi then does its final work to create digestive enzymes and removes a very specific small vesicle. That vesicle is a lysosome.

From there, the lysosomes float in the cytoplasm until they are needed. Lysosomes are single membrane organelles.

Function

Lysosomes are responsible for the digestion of macromolecules, old cell parts, and microorganisms.

The purpose of the lysosome is to digest things. They can be used to digest food or break down the cell when it dies.

Lysosomal action

Since lysosomes are little digestion machines, they go to work when the cell absorbs or eats something. Once the material is inside the cell, the lysosomes bind and release their enzymes.

Enzymes break down complex molecules that can include complex sugars and proteins.

What happens if food is scarce and the cell starves?

Lysosomes will function even if there is no food for the cell. When the signal is sent, the lysosomes digest the cells’ organelles in search of nutrients.

Lysosomal function disorders

There are approximately 30 fairly rare disorders in humans that are due to defects in endolysosomal function. All are caused by errors in the genetic code and all are lysosomal storage disorders.

In these disorders, the products accumulate in the lysosomes because the enzymes that would accelerate their degradation are absent or defective. Each disorder has a specific medical name.

Some of the better known disorders include:

  • I cell disease:  Fibroblast cell lysosomes are deficient in almost all hydrolytic enzymes, and large undigested “inclusions” accumulate in patient cells.
  • Tay-Sachs disease –  a lysosomal storage disorder in nerve cells, almost always causes premature death, but the incidence of death is now decreasing thanks to genetic testing and counseling.
  • Pompe and Gaucher:  Large amounts of lipids accumulate in lysosomes.
  • Hurler syndrome: it  involves a defect in the metabolism of mucopolysaccharides, it is a lysosomal storage disease.