Thursday, March 15, 2012

Leaving Cert Biology - Isolation of DNA

Please view photos from today's experiment on the isolation of DNA from onion cells. The reasons for each step is given below

Chopping onion:
Breaks cell walls, releasing cytoplasm.
Adding washing-up liquid:
Breaks down cell membranes, releases nuclear material from cell.
Adding salt:
Minimise attractive forces between DNA and protein, causes DNA to clump together.
Heating mixture to 60 °C for exactly fifteen mins:
Break down of DNAses enzymes. After 15 mins DNA broken down.
Cooling mixture:
Slowing down any other enzymes before they destroy DNA.
Further destroys cell walls and membranes. Causes release of DNA. Blending > 3s cuts DNA strands.
Adding protease:
Breaks down proteins associated with DNA.
Remove large cellular debris. DNA passes through filter with liquid.
Using cold ethanol:
Forms a layer on top of onion filtrate. Alcohol draws water out of DNA molecule, making it less dense - found between two liquids. DNA insoluble in freezing cold ethanol (soluble in alcohol at room temp)
Testing for DNA:
No method of testing for DNA available for use in school labs

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