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Biology Lab: Extraction of Crude DNA from Plant and Animal Tissues Essay Sample

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Biology Lab: Extraction of Crude DNA from Plant and Animal Tissues Essay Sample

Background and Purpose:

– In this experiment you will be extracting DNA from two sources: animal tissue (liver tissue) and plant tissues (kiwi). Two procedures will be followed and instructions must be followed precisely in order to obtain appropriate results.

– The purpose of this experiment is to strengthen and acquire skills of measuring, observing, predicting, collecting and recording data. We will also learn how different solutions and substances lead to the extraction of DNA.

Procedure 1: Extracting DNA from Fresh Sheep Liver

Materials: – Fresh Sheep Liver – Liquid Soap

– Scalpel or Dissecting Scissors – 95% ethanol

– Blender – 0.9% NaCl solution (saline)

– Graduated Cylinders

– Glass Stirring Rod

– Droppers

– Beakers

– Cheesecloth

Procedure and Explanations:

1- Cut a piece of liver about 2 cm long and place it with 30 ml of saline solution in a Blender. Blend till the mixture is uniform. The saline solution makes the positively charged phosphate groups in DNA neutral, thus instead of repelling each other they are drawn closer together. This leaves DNA in the solution and causing all other proteins and carbohydrates to precipitate.

2- Fold two pieces of cheesecloth in half and use it to strain the liver mixture into a beaker.

3- Use a dropper to add approximately 30 ml of liquid soap to the mixture and mix thoroughly with a glass stirring rod. The soap causes the breakdown of proteins and lipids that make up the cell and nuclear membranes allowing the DNA to escape.

4- Measure and record the volume of the soap-liver mixture that is in the beaker and then add a volume of 95% ethanol twice your measured volume. Ethanol is added to precipitate the DNA, since DNA is soluble in water, so when ethanol is added the DNA will precipitate into the alcohol layer.

5- Slowly stir the mixture with the glass stirring rod. A Whitish substance (DNA) will form where the alcohol and liver mixture meet.

6- Watch as DNA precipitates up through the ethanol. Twirl the glass rod slowly in the mixture. DNA strands will accumulate and clump together on the rod, forming a visible mass. Record you results.

Observations: – Light brownish mixture of liver-ethanol

– Small and thick whitish accumulations (DNA)

– Small bubbles forming around the DNA

Procedure 2: Extracting Crude DNA from Kiwi Fruit

Materials: – 1 Kiwi Fruit – Ice cold Ethanol

– Water Bath set at 60 oC – Glass Rod

– Crushed Ice – Detergent (washing up liquid)

– Scalpel – 3% NaCl solution (saline)

– Filter Paper

– Funnels

– Beakers/Flasks

– Test Tubes and Rack

Procedure and Explanations:

1- Chop Kiwi into small cubes, side about 0.5 cm. Cutting into small pieces gives more surface area.

2- Add chopped kiwi fruit to 10 ml detergent + 50 ml NaCl solution, in a flask or beaker. The Roles of detergent and NaCl solution is the same as in Procedure 1.

3- Hold flask/beaker in water bath at 60 oC for exactly 15 minutes. The kiwi is heated to 60 oC to speed up the breaking down of membrane walls. Heating may also destroy or deactivate certain enzymes such as DNase that can degrade the DNA that will be moving out. The timing of 15 minutes is due to the fact that DNA might defragment due to elevated heat exposure for a long period of time. This is why it is better to cool the mixture after heating. Also the DNases that were not previously destroyed can be slowed down by cooling.

4- Cool flask holding it in ice.

5- Filter through filter paper and discard kiwifruit residue. DNA is now found in the solution that has been filtered.

6- Transfer DNA solution into a test tube. Pour ice-cold ethanol carefully down the side of the tube on the surface to form an ethanol layer above the extract. The reason of why we use ice-cold ethanol is for precipitating or solidifying the DNA, since DNA will most likely precipitate if it is cooler. The cold temperature of the ethanol just increases the amount of DNA precipitated.

7- Agitate the Liquid by twisting a fine glass rod gently where the two liquids meet. This will gently cause the bubbles and DNA to precipitate to the top of the test tube.

8- Small Bubbles will attach to the DNA strands as they move up through ethanol. They are seen as opaque Stands.


– Bubbles attached to the DNA strands as the moved up the ethanol.

– The DNA strands were smaller than the animal tissue DNA.

– Solution in test tube was clear.

– Small accumulation of DNA on surface.







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