![]() The PDL takes the initial number of cells at the time when the cells start growing exponentially and the final number is counted at the end of log phase, or just before that (while still growing exponentially). The expansion rate Christina Durant prefers would take the initial number of cells as cells seeded and the final number when the cells are harvested. If one plots the number of cells on semilog paper as a function of time, one gets an initial lag phase (shorter if the solutions to which the cells are exposed during trypsinization and plating are maintained at 37 deg C, and the trypsin/EDTA concentration is the lowest that will release the cells into a single cell suspension within about a 5 min exposure (or less) at 37 deg C now one would use TrypLE, an engineered active moiety of trypsin, that does not self-digest) followed by exponential growth, and then if the cultures are not trypsinized (or diluted for suspension cultures) early enough, a plateau phase (due to nutrient and/or space exhaustion). The first mammalian cell single cell plating experiment was from T.T. I don't have a handy reference for the PDT formula, because it has been in use as far back as the 1960s for mammalian cells, and even earlier for yeast and bacteria (but see below). It should be remembered that the PDL represents an average measure of turnover that differs from the number of divisions done by the fastest growing cells because it also depends on the Growth Fraction (the fraction of cells actually prolifferating) and Cell Loss Rate (rate of loss of cells, most usually in in vivo culture). Doubling Time (Simple Interest) calculator uses Doubling Time Simple Interest 100/Annual Interest Rate to calculate the Doubling Time Simple Interest, Doubling Time (Simple Interest) is used to calculate how long it would take to double the balance on an interesting bearing account that has a simple interest. If your doubling time is in days, then your change will be a percent change per day. If your percent change is 20 per minute, then your doubling time will be measured in minutes. Otherwise, the growth curve follows a Gompertzian function rather than a simple exponential one. Also note that the time units must match. Ideally growth is exponential (except for short lag phases after trypsinization (for monolayer cultures) and a tapering off of the exponential growth due to space restrictions (contact inhibition) or nutrient depleation), with the cells kept in exponential growth all the time by appropriately frequent cell transfers. It is a particularly important number for cells that are not immortal (i.e., do not produce telomerase), because is gives an estimate as to when the cells will reach senescence. ![]() The PDL level is meant to measure the average number of population doublings of cells in culture.
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