Lysosomes

Table of Contents

• Definition
• Structure
• Lysosome in Plant Cells
• Why are Lysosomes known as Suicidal Bags?
• How do the Lysosomes Function?
• Where are Lysosomal Enzymes made?
• Lysosomal Diseases
• FAQs on Lysosomes

Lysosomes are an important cell organelle found within eukaryotic animal cells. Due to their peculiar function, they are also known as the “suicide bags” of the cell.

The term was coined by Christian de Duve, a Belgian biologist, who discovered it and ultimately got a Nobel Prize in Medicine or Physiology in the year 1974.

Let us have a detailed overview of lysosome structure, functions and diseases associated with it.

“Lysosomes are sphere-shaped sacs filled with hydrolytic enzymes that have the capability to break down many types of biomolecules.”

In other words, lysosomes are membranous organelles whose specific function is to breakdown cellular wastes and debris by engulfing it with hydrolytic enzymes.

Lysosomes are membrane-bound organelles and the area within the membrane is called the lumen, which contains the hydrolytic enzymes and other cellular debris.

The diagram below shows the lysosome structure within a cell.

Lysosome diagram showcasing enzyme complexes within the single-walled membrane

The pH level of the lumen lies between 4.5 and 5.0, which makes it quite acidic. It is almost comparable to the function of acids found in the stomach.

Besides breaking down biological polymers, lysosomes are also involved in various other cell processes such as counting discharged materials, energy metabolism, cell signalling, and restoration of the plasma membrane.

The sizes of lysosomes vary, with the largest ones measuring in more at than 1.2 μm. But they typically range from 0.1 μm to 0.6 μm.

Read more: Metabolism

As stated before, lysosomes work as the waste discarding structures of the cell by processing undesirable materials and degrading them, both from the exterior of the cell and waste constituents inside the cell.

But sometimes, the digestive enzymes may end up damaging the lysosomes themselves, and this can cause the cell to die. This is termed as autolysis, where “auto” means “self” and “lysis” means “the disintegration of the cell by the destruction of its cell membrane“.

Hence, lysosomes are known as “Suicidal Bags” of the cell.

The key function of lysosomes is digestion and removal of waste. Cellular debris or foreign particles are pulled in to the cell through the process of endocytosis. The process of endocytosis happens when the cell membrane falls in on itself (invagination), creating a vacuole or a pouch around the external contents and then bringing those contents into the cell.

On the other hand, discarded wastes and other substances originating from within the cell is digested by the process of autophagocytosis or autophagy. The process of autophagy involves disassembly or degradation of the cellular components through a natural, regulated mechanism.

Lysosomes comprise of over 50 different enzymes. They are synthesized in the rough endoplasmic reticulum.

Once synthesized, the enzymes are brought in from the Golgi apparatus in tiny vesicles or sacs, which then merges with bigger acidic vesicles.

The enzymes produced especially for lysosomes are mixed with the molecule mannose 6-phosphate making them get fixed appropriately up into acidified vesicles.

Production of enzymes of the lysosome is organized by nuclear genes. Nuclear genes are genes which are located within the nucleus of a cell, specifically in eukaryotes.

Any mutations in these genes may result in the emergence of over 30 diverse human genetic ailments, which are collectively called lysosomal storage diseases (LSD).

When such a mutation occurs, the molecules accumulate within the cell and eventually kills it. This can lead to cancer and a host of other diseases ranging from cardiovascular diseases, neurodegenerative disorders and ageing-associated ailments.

Read more: Genes

Lysosomes are predominantly found in eukaryotic animal cells and are responsible for breaking down cellular debris. In plants, the role of lysosomes is undertaken by the vacuoles as traditional cell biology dictates.

However, recent discoveries point out that the function of vacuoles is quite similar to the functions of a lysosome in animal cells. Furthermore, findings suggest that these vacuoles possess hydrolytic enzymes similar to the ones found in animal cells.

So some botanists have challenged the definition of a vacuole. In other words, it sparked a controversy that pits the definition of the two cellular organelles, with some saying that both perform similar tasks.

Summary

• Lysosomes are cell organelles almost exclusively found in eukaryotic animal cells

• Lysosomes are membrane-bound spherical sacs filled with hydrolytic enzymes

• These enzymes can break down many types of biomolecules such as proteins and fats

• They are not found in plants, but vacuoles perform the role of lysosomes in plant cells

• Lysosomes are known as Suicidal Bags as they tend to destroy the cell membrane with its digestive enzymes,  causing lysis of the cell (also called autolysis)

• Lysosomal enzymes are synthesized in the rough endoplasmic reticulum, where they are brought in by the Golgi apparatus through tiny vesicles. It eventually merges with bigger acidic vesicles

• Mutations of the nuclear gene may result in the emergence of rare, diverse human genetic ailments, which are called lysosomal storage diseases or LSD

Explore more fascinating facts about Lysosome, its definition, structure, function, and diagram, by exploring BYJU’S Biology

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Further Reading:

• Difference Between Plant cell and Animal cell
• Prokaryotic Cells
• Eukaryotic Cells
• Competent Cells