Lysosome – Its structure and function

History of lysosome:

       Christian de Duve, a Belgian biologist, discovered lysosomes and was given the 1974 Nobel Prize in Physiology or Medicine. He is also credited with the discovery of peroxisomes, which are other cellular organelles. De Duve and Novikoff used optical and electron microscopy to confirm the location of the hydrolytic enzymes of lysosome using an acid phosphatase staining technique.

Define lysosome

      Simple little spherical sac-like structures called lysosome (plural: lysosomes) are found in the cytoplasm. Because they trigger cell death, they are referred to as suicide sacks. Although their shape is typically variable, lysosomes are typically rounded. The inside of lysosomes can either be nearly solid or can be divided into an outside, more dense region, and an inner, less dense mass that contains granules.

       With the exception of red blood cells, they exist in all animal cells. Lysosomes are abundantly found in leucocytes, macrophages, Kupffer’s cells, and other phagocytic cells in mammals. They can be found in Euglena, fungus, maize, cotton, and pea seed root tip cells. In other plants, phagosomes, aleurone grains, and vacuoles all serve the same purpose as lysosomes.

         Lysosomes are specialized vesicles found inside cells that break down big molecules using hydrolytic enzymes. Vesicles, which are little fluid spheres encased in a lipid bilayer membrane, are involved in the movement of chemicals inside the cell.

       A human cell has about 300 lysosomes, which are only present in animal cells. They are in charge of not just breaking down and eliminating cell waste, but also digesting big substances. These functions are made possible by the more than 60 distinct enzymes that are present in lysosomes.

Why lysosomes are known as suicide sacks?

      They are equipped with hydrolytic enzymes including proteases, lipases, and nucleases that can degrade any kind of biological polymer, such as proteins, nucleic acids, carbohydrates, and lipids, that enters the cell or that the cell no longer needs. When a cell dies, the lysosomes release some enzymes that break down the cell waste, and they can even digest their own proteins through a process called autolysis. As a result, they are known as “suicide bags”.

Explain the types of lysosomes.

    Based on their appearance and function, lysosome can be divided into four different categories.

Primary lysosomes:

       Their Golgi apparatus vesicles have just been pinched off. The primordial lysosomes are tiny and are filled with granules of hydrolytic enzymes.

Secondary lysosome:

       It is also known as a digesting vacuole or a heterophagosome. A phagosome that contains food and a lysosome combine to generate a secondary lysosome. Remaining Bodies (Residual or Tertiary Lysosomes). They are those lysosomes that only contain non-digestible food components.

Self-Eating Vacuoles ( Autophagosome, Autolysosomes):

     They are created by the fusion of many primary lysosomes around worn-out or degenerated intercellular organelles that have been digested. The process, also known as autophagy or autodigestion, aids in the elimination of cell waste. Lysosomes are referred to as disposal units or disposal bags as a result.

What is the structure of lysosome?

      The size of Lysosomes is typically relatively small, measuring between 0.2 to 0.3 µm, yet they can grow as large as 1.2 m. They are spheres comprised of a lipid bilayer that surrounds fluid containing a variety of hydrolytic enzymes, and they have a straightforward structure. Phospholipids, which are molecules with hydrophilic phosphate group heads, a glycerol molecule, and hydrophobic fatty acid tails, are the lipids that make up the bilayer.

       Phospholipids naturally form double-layered membranes when dissolved in a solution containing water as a result of these variances in characteristics. While the fatty acid tails go to the interior of the layer to avoid contact with water, the phosphate group heads move to the outside of the layer. Numerous additional membranes in the cell, including the nuclear membrane (or nuclear envelope) that encloses the nucleus, the Golgi apparatus, and the endoplasmic reticulum, are composed of phospholipids.

         The hydrolytic enzymes that makeup lysosomes are produced in the endoplasmic reticulum once they sprout off of the Golgi apparatus. The enzymes are carried in vesicles to the Golgi apparatus, where they are packaged into the lysosomes after being labeled with the mannose-6-phosphate molecule.

        Proteases, amylases, nucleases, lipases, and acid phosphatases are just a few of the numerous kinds of enzymes found in lysosomes. The molecules that an enzyme degrades are typically the names of the enzymes; for instance, proteases degrade proteins, while nucleases degrade nucleic acids. Starches are converted into sugars by amylases.

     Liposomes, which should not be confused with lysosomes, are engineered vesicles that include phospholipid bilayers like other vesicles do, including lysosomes. They are occasionally employed to deliver pharmaceuticals and nutrition.

Explain the function of lysosomes.

      Numerous complex substances, including lipids, proteins, nucleic acids, and carbohydrates, are broken down by lysosomes before being recycled by the cell. Because their hydrolytic enzymes work better at this pH than at the neutral pH of the rest of the cell, lysosomes have an acidic pH (about pH 5).

      Large molecules are particularly hydrolyzed by hydrolytic enzymes. A substance undergoes hydrolysis when a water molecule is added, causing it to split. The lysosome can be considered the “digestive system” of the cell since it breaks down molecules using enzymes, similar to how the digestive system of the human body breaks down food using enzymes.

      Multiple kinds of chemicals are broken down by lysosomes. If they merge with an endocytic vesicle, which is a vesicle that transports particles into the cell, they can break down food molecules that enter the cell into smaller bits. They have the ability to destroy organelles that are not functioning properly through a process called autophagy. The process of phagocytosis, sometimes known as “cell eating,” occurs when a cell engulfs a molecule in order to break it down. Lysosomes play a role in this process.

   For instance, in order to digest and eliminate invading bacteria, white blood cells known as phagocytes swallow the bacteria, which is then trapped in a vesicle that lysosomes fuse with. The bacteria are then destroyed by these lysosomes.

Lysosomal disease:

     Nuclear genes coordinate the lysosome’s enzyme production. Particularly in eukaryotes, nuclear genes are those that are found in the cell’s nucleus. Over 30 different human genetic disorders known as lysosomal storage diseases may develop as a result of any abnormalities in these genes (LSD).

    When such a mutation takes place, the molecules build up inside the cell and finally cause it to die. This can result in cancer as well as a variety of other illnesses, such as cardiovascular diseases, neurological disorders, and illnesses linked to aging.

Explain lysosomes in plant cells.

   Lysosomes are important for dissolving cellular waste and are mostly present in eukaryotic animal cells. According to conventional cell biology, the vacuoles play the lysosomes’ function in plants.

   Recent research has shown that vacuoles’ functions are actually pretty similar to those of lysosomes in animal cells. Additionally, evidence points to the presence of hydrolytic enzymes in these vacuoles that are comparable to those in animal cells.

   Therefore, some botanists have questioned what exactly constitutes a vacuole. In other words, it created a debate over the two cellular organelles’ definitions, with some arguing that they have similar functions.

What is the summary of lysosomes?

  • Cell organelles called lysosomes are nearly exclusively present in eukaryotic animal cells.
  • Hydrolytic enzymes are contained in membrane-bound spherical sacs called lysosomes.
  • These enzymes may disintegrate a wide variety of macromolecules, including proteins and lipids.
  • Although vacuoles are absent from plants, they serve as lysosomes in plant cells.
  • Due to their propensity to lyse cells by destroying the cell membrane with their digesting enzymes, lysosomes are known as “Suicidal Bags” (also called autolysis)
  • The Golgi apparatus transports lysosomal enzymes into the rough endoplasmic reticulum, where they are produced. Later, it combines with larger acidic vesicles.
  • Lysosomal storage disorders, or LSD, are a group of uncommon, heterogeneous human genetic conditions that can arise from mutations in the nuclear gene.


Rimsha Bashir
Rimsha Bashir

Rimsha Saith is a highly knowledgeable microbiologist with a keen interest in the field. Her expertise and passion are in her writing for Microbiology. As a writer, Rimsha has authored numerous articles that have been well-received by both health and medical students and industries.

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