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
older
the deeper you dig into the earth, the farther back into history you are going.
Answer:
Water (H2O) is drawn out of two small molecules to combine them into one large molecule
un animal es como una jirafa o un pez o un perro etc. pero tambien ay animales invertebrados o vertebrados
vertebrados se inifica que tiene un esqueleto interno articulado lo que ucal permite que se puedan mover , ejemplos de animals vertebrados son un pinguino elefante cocodrilo perro etc
invertebrado se inifica que son animales que no tienen colbna vertebral ejemplos son mariposas ,gusanos ,medusas ,caracoles etc
ojala te ayude jjejejej