Biology Lab 2 - Methods Report Dna Isolation from Banana Cells

To begin the experiment, a 1cm3 piece of banana was cut and mixed with a pinch of sand in a mortar, and mashed up with a pestle. Using a pipette, 10mL of detergent/ salt solution was measured and added to the mortar. The mixture was then ground for four minutes. Next, a funnel was lined with cheesecloth, and the liquid was poured through it and into a clean test tube. With a clean pipette, 4mL of enzyme solution was measured and added to the test tube. After swirling for two minutes, 10mL of cold 95% ethanol was slowly added to the test tube by pouring it from a graduated cylinder down the inside of the test tube. Caution was taken when dealing with the ethanol, it is extremely flammable and can be harmful if inhaled or consumed. The ethanol created a clear layer on the top of the mixture. After five minutes, the DNA was visible in the ethanol. Using the end of a pipette, the DNA was collected and removed from the test tube. Observations were recorded, and all apparatus cleaned and put away. Any waste containing ethanol was disposed of in the fume hood.

Lab 2 - Questions

1. Why did we grind banana with a pinch of sand and detergent?

When the sand is ground with the banana it breaks up the plant cell walls and the detergent gets in the cell and breaks up the nuclear membrane, that the DNA is inside.

2. Why was table salt (NaCl) used?

When NaCl dissolves in solution it ionizes. In DNA isolation, the Na+ ions bond with the negatively charged phosphate groups on the DNA strands. The DNA strands are no longer held apart by the negative charges, so they clump together. This helps for when the ethanol is added to solidify the DNA.

3. Why was an enzyme solution (pineapple juice) used?

Certain enzymes help to break apart proteins into amino acids. In this experiment, the enzyme bromelain breaks up the group of proteins called histones, that create nucleosomes and that DNA strands are wrapped around.

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