DNA extraction

Materials Required

• Cells grown from yesterday
• Centrifuge
• Pipette
• Lysozyme
• Cell lysis solution
• RNase solution
• Protein precipitation solution
• DNA hydration solution
• Isopropanol
• 70% ethanol

Procedures

Cell lysis

1. Pellet cells by centrifugation at 3600 rpm for 10 minutes.
2. Pour off supernatant.
3. Add 0.5 ml of cell suspension solution, gently pipet up and down to resuspend and transfer to 1.5 ml eppendorf tube.
4. Add 25 μl of lysozyme and invert tube 25 times.
5. Incubate for 30 minutes at 37°C while inverting the tube occasionally.
6. Centrifuge at 13000 rpm for 10 minutes to pellet the cells, then remove the supernatant.
7. Add 0.5 ml of cell lysis solution to the cell pellet and gently pipet up and down to lyse the cells.
8. Heat sample for 30 minutes and mix every 5-10 minutes.

RNase treatment

1. Add 3 μl of RNase A solution to the cell lysate
2. Mix by inverting 25 times and incubate at 37°C for 60 minutes

Protein precipitation

1. Cool samples on ice.
2. Add 0.5 ml of protein precipitation solution to each tube.
3. Invert the tubes to mix the protein precipitation solution uniformly with the cell lysate.
4. Place samples on ice for 5 minutes.
5. Centrifuge at 13000 rpm for 30 seconds or until the precipitated proteins form a tight pellet.

DNA precipitation

1. Pour the supernatant containing the DNA into a clean eppendorf tube. (The samples may be kept at -20°C overnight at this stage.)
2. Add 0.5 ml isopropanol to each tube.
3. Mix by inverting gently for 50 times.
4. Centrifuge at 13000 rpm for 1 minute. The DNA should be visible as a small white pellet.
5. Pour off the supernatant and drain the tube on a clean absorbent paper.
6. Add 0.5 ml of 70% ethanol and invert the tube several times to wash the DNA.
7. Centrifuge at 13000 rpm for 1 minute. Carefully pour off the ethanol.
8. Drain the tubes on clean absorbent paper. Allow to air dry for 10-15 minutes.

DNA hydration

1. Add 100 µl DNA hydration solution to each tube.
2. Rehydrate DNA by incubating the sample for 1 hour at 65°C, followed by overnight incubation at room temperature. Tap the tube periodically to aid in dispersing the DNA.
3. For storage, centrifuge briefly and store at -20°C.

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