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Thread: Harvest-passaging

  1. #1 Harvest-passaging 
    Forum Freshman
    Join Date
    Oct 2007
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    can somebody explain me what is the means of these words??, I don't understand the concepts of this...and I also I don't understand:scraping with a policeman...is in this context:

    for a relatively small number of cell lines, it is possible to mechanically dislodge the cell using a "policeman", which is a device that has a beveled edge and a handle.harvesting of cells by scraping, some cells can be scraped(rather than treated with trypsin) following treatment with EDTA.For many assays, particularly those in which cells extracts are to be obtained, scraping with a policeman is carried out in a buffer that promotes cell lysis and contains appropriated inhibitors and nuclease. that advantage is that cells can be scraped rapidly into a small volume of lysis buffer and processed quicky.


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  3. #2  
    Forum Professor
    Join Date
    Sep 2007
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    Hello Kitty,

    In tissue culture, cells typically adhere (stick) to a culture vesicle (which is usually a flask.) The growth medium (oftentimes a reddish blood-based medium) bathes the cells and becomes orange-y as the cells grow and acidify (and use up) the medium. As the cells grow, they also begin to crowd out each other, growing in a very crowded layer on the surface of the flask.



    Below is an image showing a young culture and an old culture. The image is grey because it was taken under the microscope, without colour:



    When the cells become crowded, as on the right, they signal to each other to stop growing. In order to keep the cells growing, they must be passaged into a new flask, with fresh media.

    A time-honoured straightforward way to do this, is to scrape some of the the cells out of the flask, with a rubber policeman:



    (not very high-tech, is it.) One does not need to passage all of the cells, in fact it would be counter productive to do so. One merely needs to get a good number into the fresh flask, with fresh medium, and they will then adhere and begin to grow again. If I recall correctly, typical cells must be passaged once or twice a week.

    Trypsin is an alternative method to dislodging the cells. Trypsin is a protease, and it destroys the adhesins that attach the cells to the flask. If you bathe the crowded cells with trypsin, they will all come off very easily. However, this is very stressful for the cells and you don't want all of them anyway.

    Hope that helps?


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  4. #3  
    Forum Freshman
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    Oct 2007
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    thank you!! Now I can understand it :-D
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