Chinese hamster ovary cell production of recombinant tissue‐type plasminogen activator (t‐PA) was increased by amplification of cotransfected dihydrofolate reeducates cDNA using stepwise adaptation to increasing methotrexate (MTX) concentrations. The highest producing clones were isolated at 5 μM MTX and yielded 26,000 U/106 cells/day t‐PA (43 μg/106 cells/day). Above 25 μM MTX, cell specific t‐PA production rates became increasingly variable and the cDNA copynumbers decreased. No apparent correlation between the cell specific t‐PA production rate and the growth rate was observed upon sub cloning of the amplified cells. When MTX selection was removed, the t‐PA production rate decreased up to tenfold within 40 days; this was accompanied by an up to 60% drop in cDNA copynumber. Subclones isolated after 108 days of culture in the absence of MTX were, on average, sixfold more stable than their parental cells. In culture without MTX, the maximum stable t‐PA production rate obtained (over 250 days) was 7000 ± 750 U/106cells/day (∼12 μg/106 cells/day), approximately threefold lower than the maximum unstable levels of production reached under selective pressure. Taken together, these results define a wide range of the highest t‐PA expression rates obtained under MTX selection, for which stable expression without selection has not been reported
In order to actually start up the Scientific method you must "Observe" whatever it is you want to question.
The given case describes the situation of emotional arousal.
The emotional arousal is the state, in which the alertness of the body increases due to the increase in the emotions.
In this case, the death of the woman's aunt, leaves a emotional remark to her. As she knows that smoking causes lung cancer, she feels very emotional and quits smoking.
Populations are influenced by fluctuations in any of the abiotic cycles. The fluctuations of seasonal cycles can cause populations to hibernate, migrate, or breed. Organisms breed as a result of seasonal fluctucations that cause them to have a limited resource supply. Fluctuations in the phosphorus cycle can cause <span>changes to aquatic ecosystems, either positive or negative.</span>
Not they don't each cell is individual they don't connect
