Lysis
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Lysis (Greek λύσις, lýsis from lýein "to separate") refers to the breaking down of a cell, often by viral, enzymic, or osmotic mechanisms that compromise its integrity. A fluid containing the contents of lysed cells is called a "lysate".
Many species of bacteria are subject to lysis by the enzyme lysozyme, found in animal saliva, egg white, and other secretions.[1] Phage lytic enzymes (lysins) produced during bacteriophage infection are responsible for the ability of these viruses to lyse bacterial cells.[2] Penicillin and related β-lactam antibiotics cause the death of bacteria through enzyme-mediated lysis that occurs after the drug causes the bacterium to form a defective cell wall.[3] If cell wall is completely lost, the bacterium is referred as a protoplast if penicillin was used on gram-positive bacteria, and spheroplast when used on gram-negative bacteria.
Cytolysis
Cytolysis is the lysis of cells in a hypotonic environment (the surrounding fluid has a lower salt concentration than the cell interior). Cytolysis is caused by excessive osmosis, or movement of water, toward the inside of a cell (hyperhydration). The cell membrane cannot withstand the osmotic pressure of the water inside, and so it explodes. Osmosis occurs from a region of high water potential to a region of low water potential passing through a semipermeable membrane, so these bursting cells are located in hypotonic environments.
Cytolysis can be prevented by several different mechanisms, including the contractile vacuole that exists in some paramecia, which rapidly pump water out of the cell.
Cytolysis does not occur under normal conditions in plant cells because plant cells have a strong cell wall that contains the osmotic pressure, or turgor pressure, that would otherwise cause cytolysis to occur.
Plasmolysis
Plasmolysis is the contraction of cells within plants due to the loss of water through osmosis. In a hypertonic environment, the cell membrane peels off of the cell wall and the vacuole collapses. These cells will eventually wilt and die unless the flow of water caused by osmosis can stop the contraction of the cell membrane.[4]
- Main article: Red blood cell#Secondary functions
Erythrocytes' hemoglobin release free radicals in response to pathogens when lysed by them. This can damage the pathogens.[5][6]
Applications
Cell lysis (splitting of cells) is used to break open cells when it is desirable to avoid shear forces that would denature or degrade sensitive macromolecules, such as proteins and DNA. For example, lysis is used in western and Southern blotting to analyze the composition of specific proteins, lipids, and nucleic acids individually or as complexes. Depending upon the detergent used, either all or some membranes are lysed. For example, if the cell membrane only is lysed then gradient centrifugation can be used to collect certain organelles.
References
- ^ Fastrez, J. Phage Lysozymes In: Lysozymes--model enzymes in biochemistry and biology, Pierre Jollès editor, Birkhäuser, 1996, pp. 35-64.
- ^ Nelson, D., Loomis, L. & Fischetti, V. A. (2001). Prevention and elimination of upper respiratory colonization of mice by group A streptococci by using a bacteriophage lytic enzyme. Proceedings of the National Academy of Sciences, USA 98, 4107–12.
- ^ Scholar, E. M., Pratt W. B. The antimicrobial drugs, Oxford University Press US, 2nd ed., 2000, pp. 61-64.
- ^ "Wiley InterScience : Journals : New Phytologist". www3.interscience.wiley.com. Retrieved 2008-09-11.
- ^ Red blood cells do more than just carry oxygen. New findings by NUS team show they aggressively attack bacteria too., The Straits Times, 1 September 2007
- ^ Jiang N, Tan NS, Ho B, Ding JL (2007). "Respiratory protein-generated reactive oxygen species as an antimicrobial strategy". Nature Immunology. 8 (10): 1114–22. doi:10.1038/ni1501. PMID 17721536.
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