How is cell viability measurement performed?
Cell viability measurement determines living cells in a culture and is essential for evaluating pesticide effectiveness, toxin damage, and drug potential. Two main types of viability assays are used for this purpose.
Dye exclusion viability assays use dyes like trypan blue or propidium iodide that enter dead cells and intercalate with DNA. Live cells exclude the dye due to intact membrane integrity, while dead cells allow dye entry, indicating loss of membrane integrity.
Metabolic viability assays rely on cells' ability to execute biochemical reactions measured through absorbance, fluorescence, or luminescence. In the MTT assay, yellow MTT reacts with mitochondrial dehydrogenase enzymes of live cells, reducing to purple formazan crystals proportional to cell number.
Explanation
The textbook describes two methods for cell viability determination. Dye exclusion assays work on the principle of membrane integrity - live cells have intact membranes that exclude dyes, while dead cells allow dye entry. Metabolic assays like MTT measure cellular biochemical activity, where the amount of product formed (formazan) is directly proportional to the number of living cells.