What is Cell Lysis?
A cell is a biological living unit which is typically an enclosed space containing specialized components called organelles.
The inside of a cell is filled with a fluid called the cytoplasm and the entire cell shape is maintained because of the plasma/ cell membrane.
The cell membrane is semi-permeable and is made up of components that contributes to its structural integrity.
Bacteria also have a cell wall, which provides them with an additional layer of protection.
It is important for the cell to regulate its own functions and prevent any kind of compromise to its morphology.
Cell lysis refers to the breakage of the plasma membrane or the cell wall and leakage of the cellular contents, eventually resulting in cell death.
It is exhibited by both eukaryotic and prokaryotic cells.
Understanding cell lysis is necessary as it can not only help us comprehend the mechanism behind it, we can also exploit those mechanisms for experimental studies.
Lysis is brought about by specialised proteins which compromise the cell membrane, and in case of prokaryotes, the cell wall, or by external agents such as detergents or mechanical means.
Types of Cell Lysis
Cytolysis occurs when a cell bursts due to an osmotic imbalance that has caused excess water to move into the cell.
Oncolysis is the destruction of neoplastic cells or of a tumour.
Plasmolysis is the contraction of cells within plants due to the loss of water through osmosis.
Erythrocytes’ hemoglobin release free radicals in response to pathogens when lysed by them.
Natural Cell Lysis
Cell lysis is exhibited by various types of cells and although the end result is cell death, this mechanism serves to benefit either the causative organism or the host organism.
Described below are some ways in which cell lysis takes place in nature.
a. Virus Mediated Cell Lysis
Bacteriophages are a type of virus which infect bacterial cells and use the latter for their replication and survival.
Bacterial cell lysis due to a viral attack is one of the ways in which the viral particles can be released from the host cell after multiplication.
Since the bacterial cell wall is composed of peptidoglycan (a polymer), specialized proteins called enzymes are released to disrupt the cell membrane and cell wall.
Holin, endolysin and spannin are three such enzymes involved in this mode of lysis.
Holins are the enzymes which control the timing of cell lysis.
They keep accumulating near the cell membrane and when the viral particles are ready to be released outside the cell, they cause the formation of holes in the bacterial cell wall.
Endolysins are the enzymes which can access the cell wall via these holes and actually attack the bonds between the building blocks of peptidoglycan of the cell wall, thereby degrading it.
Spannins disrupt the outermost membrane of the bacterial cell.
Single stranded DNA phages have certain genes that prevent the synthesis of peptidoglycan components and result in a weakened cell wall and causing lysis.
Significance: Viruses increase their infectivity by causing lysis of bacterial cells and releasing their progeny.
b. Cell Lysis in Cell Death Pathways
In mammalian cells, different intracellular pathways are activated when there is a bacterial or viral infection.
Such pathways lead to cell death as that can be beneficial to limit the infection since it would reduce the number of cells required by the foreign organism to invade.
Cell lysis, as described earlier, involves disruption of the cell membrane.
The cell membrane is made up of molecules called phospholipids, which are basically phosphate groups attached to a lipid molecule.
Infection in mammalian cells results in a process called inflammation, which is simply the activation of immune system.
Inflammation results in activation of specialised enzymes called caspases when a cell requires to go into ‘death’.
These caspases activate proteins which can bind to the phospholipids of the cell membrane, form pores and result in cell swelling and lysis.
Significance: Lysis of mammalian cells infected by bacteria/viruses causes reduced infection potential of the latter.
c. Immune Cell Mediated Cell Lysis
Immune cells such as T-cells have the property to recognize foreign bodies called antigens.
They release granules which contain proteins called perforins.
These attack the antigens, cause pore formation and result in bursting of the foreign cells.
Significance: Immune cells can directly kill foreign bodies via cell lysis.
Artificial Methods of Cell Lysis
Experimental research in biology requires studies on cellular components.
Hence, artificial methods of lysing cells have been developed.
Some of those techniques have been described below.
a. Osmotic Cell Lysis
Cells maintain their size due to their surroundings which contain fluids that prevent excess inflow (endosmosis) or outflow or water (exosmosis).
Transferring cells to solutions (example- sucrose) with a different concentration as compared to the cytoplasm can cause endosmosis, causing swelling and lysis.
b. Detergent Mediated Cell Lysis
Detergents are compounds which have both water loving and water hating components, and that makes them an ideal candidate to disrupt the cell membrane.
Example- SDS, Triton-X.
c. Physical Breakage
Beads and rotating blades can cause physical damage to the cell membrane and result in lysis.
Cell Lysis Disease: Hemolytic Anaemia
Red blood cells (RBCs) have a lifespan of 120 days.
In abnormal conditions such as pathogen attack or when the immune cells of the body mistakenly characterize RBCs as foreign cells, the cell membrane of RBCs get disrupted and they die before the end of their lifespan.
This drastically reduces RBC count in the body and results in anaemia.
Applications of Cell Lysis
Cell lysis is a widely used method for intracellular studies.
Proteins, DNA and RNA and extracted by a combination of lysis methods.
Industrially useful products generated in the intracellular space by micro-organisms are also obtained by lysing their cells.