Lysosomes – Definition, Types, Significance, Functions

A cell performs different functions with the help of its various membrane-bound organelles present in it. It has to secrete cell products, for example, enzymes, hormones, mucus, etc. Moreover, it has to digest those substances which are taken up by the cell during endocytosis. Furthermore, it has to generate energy,e.g., the synthesis of energy-rich ATP(adenosine triphosphate) by mitochondria.

A membrane is an astonishing cellular structure. Every cell is surrounded by a membrane and thus separates its own content from the outer environment. cell organelles are “small organs” of the cell and are found embedded in the cytosol. There are different cell organelles present inside a cell such as ER(endoplasmic reticulum), Ribosomes, Cytoplasm, Lysosomes, etc.

Lysosomes

Lysosomes are simple tiny spherical sac-like structures present in the cytoplasm. Lysosomes are single membrane organelle found in eukaryotic cells. They are known as suicidal bags because it leads to the death of cells. Lysosomes are generally rounded but can be irregular in outline. The interior of lysosomes may be almost solid or differentiated into an outer denser region and a central less dense mass with granular content. They occur in all animal cells with the exception of red blood corpuscles. In animals, lysosomes are present in plenty amount in leucocytes, macrophages, Kupffer’s cells, and similar cells with phagocytic activity. They are present in fungi, Euglena, root tip cells of maize, cotton, and pea seeds. In other plants, the function of lysosomes is shared by phagosomes, aleurone grains, and vacuoles.

Lysosomes are formed by the joint activity of the endoplasmic reticulum and Golgi complex. Lysosomes do not burst in the cytoplasm. All materials that have to be acted upon by lysosome enzymes are usually enclosed inside vacuoles and the vacuoles fuse with the lysosomes for the digestion of materials. Thus, lysosomes take part in the intracellular digestion of various types of materials of endogenous or exogenous origin, extracellular digestion can be performed by them under certain conditions. Lysosomes pass through various stages in the same cell. The phenomenon is called polymorphism (the existence of more than one morphological form).

Why Lysosomes are Known as Suicidal Bags?

They contain hydrolytic enzymes like proteases, lipases, and nuclease that are capable of breaking down all types of biological polymers (e.g. proteins, nucleic acids, carbohydrates, and lipids) that enter the cell or are no longer useful to the cell. When a cell dies, the lysosomes released some enzymes which digest the cell debris, and even it is able to break its own proteins by the process of autolysis. Thus, they are referred to as “suicide bags”.

Types of Lysosomes

There are four types of lysosomes depending on their morphology and function.

1. Primary Lysosomes. They have newly pinched-off vesicles from the Golgi apparatus. The primary lysosomes are small in size and contain hydrolytic enzymes in the form of granules.
2. Secondary Lysosomes. Also called heterophagosome or digestive vacuole. A secondary lysosome is formed by the fusion of a food-containing phagosome with a lysosome.
3. Residual Bodies(Residual or Tertiary Lysosomes). They are those lysosomes in which only indigestible food materials have been left.
4. Autophagic Vacuoles( Autophagosome,Autolysosomes). They are produced by the fusion of a number of primary lysosomes around worn-out or degenerated and digested intercellular organelles. The phenomenon also called autophagy or autodigestion, helps in the disposal of cell debris. Therefore, lysosomes are also called disposal bags or disposal units.

Significance of Lysosomes

• In WBC or leucocytes. Cells of leucocytes digest foreign proteins, bacteria, and viruses.
• In autophagy. During starvation, the lysosomes digest stored food contents such as proteins, fats, and glycogen of the cytoplasm and transport the necessary amount of energy to the cell.
• In metamorphosis(Frog). During the transformation of a tadpole into a frog, the embryonic tissues such as gills and tail are digested by the lysosomes and utilized by other body cells.
• In fertilization. The lysosomal enzymes present in the acrosome of sperm cells digest the limiting membrane of the ovum(egg). Thus, the sperm is able to enter the ovum and start fertilization.

Functions of Lysosomes

• They take part in the digestion of food obtained through phagosomes known as intercellular digestion.
• Lysosomes release their enzymes to the outside through exocytosis to perform extracellular digestion.
• Lysosomes destroy the obstructing structures.
• In sperms, lysosomes provide enzymes for breaking the limiting membrane of eggs.
• Leucocyte granules are derived from lysosomes.
• Lysosomes cause the breakdown of aging and dead cells.

Frequently Asked Questions

Question1: Why lysosomes are called suicidal bags?

Answer:

They contain hydrolytic enzymes like proteases, lipases, and nuclease that are capable of breaking down all types of biological polymers (e.g. proteins, nucleic acids, carbohydrates, and lipids) that enter the cell or are no longer useful to the cell. When a cell dies, the enzymes released by the lysosomes clear the cell debris and even it is able to break its own proteins by the process of autolysis. Thus, they are referred to as “suicide bags”.

Question2: Write two functions of Lysosomes.

Answer:

1. Lysosomes destroy the obstructing structures.
2. Lysosomes cause the breakdown of aging and dead cells.

Question3: What is the significance of Lysosome in fertilization?

Answer:

The lysosomal enzymes present in the acrosome of sperm cells digest the limiting membrane of the ovum(egg). Thus, the sperm is able to enter the ovum and start fertilization.

Question4: write about the structure of Lysosome.

Answer:

Lysosomes are simple tiny spherical sac-like structures present in the cytoplasm. Lysosomes are single membrane organelle found in eukaryotic cells.

Question5: Where did Lysosomes are present in animal cells?

Answer:

They occur in all animal cells with the exception of red blood corpuscles. In animals, lysosomes are present in plenty amount in leucocytes, macrophages, Kupffer’s cells, and similar cells with phagocytic activity.

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