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Pass4sure Hot 15 Certification Exams In June, 2009

sweetynico66 | 02 June, 2009 07:15

Pass4sure Hot 15 Certification Exams In June, 2009

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Pass4sure Hot 15 Certification Exams List:

  1. BSCI - Building Scaleable Cisco Internetworks: 642-901
  2. BCMSN - Building Converged Cisco Multilayer Switched Networks: 642-812
  3. Network+ Certification Exam: n10-003
  4. Composite: 642-892
  5. MCP Managing and Maintaining a Microsoft Windows Server 2003 Environment: 70-290
  6. Interconnecting Cisco Networking Devices Part 1: 640-822
  7. Securing Networks with ASA Advanced: 642-515
  8. CCIP BGP + MPLS Exam (BGP + MPLS): 642-691
  9. Pro:Windows Server 2008, Enterprise Administrator: 70-647
  10. MCSE Planning, Implementing, and Maintaining a Microsoft Windows Server 2003 AD Infrastructure: 70-294
  11. TS:Exchange Server 2007, Configuring: 70-236
  12. TS:MS SQL Server@ 2008,Implementation and Maintenance: 70-432
  13. ADVDESIGN: 352-001
  14. Applications in Microsoft Dynamics CRM 4.0: MB2-632
  15. Cisco Unity Design and Networking (CUDN): 642-072

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Cryopreservation of Cell Lines

sweetynico66 | 30 July, 2008 03:42

The aim of cryopreservation is to enable stocks of cells to be stored to prevent the need to have all cell lines in culture at all times. It is invaluable when dealing with cells of limited life span. The other main advantages of cryopreservation are:

  • Reduced risk of microbial contamination
  • Reduced risk of cross contamination with other cell lines
  • Reduced risk of genetic drift and morphological changes
  • Work conducted using cells at a consistent passage number
  • Reduced costs (consumables and staff time)

There has been a large amount of developmental work undertaken to ensure successful cryopreservation and resuscitation of a wide variety of cell lines of different cell types. The basic principle of successful cryopreservation is a slow freeze and quick thaw. Although the precise requirement may vary with different cell lines as a general guide cells should be cooled at a rate of –1oC to –3oC per minute and thawed quickly by incubation in a 37oC waterbath for 3-5 minutes. If this and the additional points given below are followed then most cell lines should be cryopreserved successfully.

  1. Cultures should be healthy with a viability of >90% and no signs of microbial contamination.
  2. Cultures should be in log phase of growth (this can be achieved by using pre-confluent cultures i.e. cultures that are below their maximum cell density and by changing the culture medium 24 hours before freezing).
  3. A high concentration of serum/protein (>20%) should be used. In many cases serum is used at 90%.
  4. Use a cryoprotectant such as Cell Culture Plate(6 well plate, 24 well plate, 96 well plate) or glycerol to help protect the cells from rupture by the formation of ice crystals. The most commonly used cryoprotectant is DMSO at a final concentration of 10%, however, this is not appropriate for all cell lines e.g. HL60 where DMSO is used to induce differentiation. In such cases an alternative such as ELISA Plate should be used (refer to data sheet for details of the correct cryoprotectant). Sigma also offers ready-made cell freezing media containing DMSO , glycerol and a serum-free formulation containing DMSO.

Source: SIGMA-ALDRICH

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