2. Introduction

3. Deoxyribonucleic acid (DNA) and Ribonucleic acid (RNA) are two types of nucleic acids. In DNA, nucleic acid are macromolecules exist as polymers called polynucleotides. It consists of monomers called nucleotides. According to Pauling.L (1953), Nucleotide consists of a nitrogenous base, a pentose sugar and phosphate group.

4. There are 2 families of nitrogenous bases 1. Pyrimidines (cytosine and thymine) have a nitrogen atom and single six-membered ring. 2. Purines (adenine and guanine) have a six- membered ring fused to a five-membered ring.

5. According to Watson et al. (1953), DNA molecules have two polynucleotides, forming a double helix. In the DNA double helix, the two backbones run in opposite directions, which referred to as antiparallel.

6. Nitrogenous bases in DNA pair up and form hydrogen bonds. According to Chargaff.E (1952) Adenine(A) always with thymine(T), and guanine(G) always with cytosine(C).

7. To form polynucleotide, nucleotides are bonded by phosphodiester bond which are formed in between 3’ of hydroxyl group and 5’ of phosphate group by condensation reaction.

8. DNA can be extracted from various types of cells. For our proposal, we are going to do DNA extraction of the same mass of strawberry. Starwberry is an octoploid, which means it have 8 haploid chromosomes. This is the ideal fruit to use in DNA extraction.

9. Objectives: To extract DNA from strawberry in its purified form. To investigate how different amount of salt will affect the DNA precipitate. Hypothesis: DNA in the strawberries can be precipitate out. When the amount of salt used during the extraction increase, the amount of DNA precipitate will be increased.

11. pipette beaker Mortar and pistle sieve Filter paper

12. Glass rod knife Water bath Electronic balance

13. Material

14. Distilled water Pineapple juice(proteolytic enzyme detergent alcohol

15. strawberry

17. 1. To prepare buffer solution, pour 3 g of salt and 80 cc of distilled water in a 50 cc beaker; - mix until the salt is completely dissolved; - with the syringe, take 10 cc of liquid detergent and add it to the solution; 2. add distilled water until you obtain a total volume of 50 cc; 3. while avoiding to produce bubbles, mix to homogenize the solution; 4. the extracting solution is ready.

18. 5. Place 25 g of strawberry (without peel) on a chopping board and crush it with a mortar and pestle until obtain a pulp.- pour the mush in a 250 cc beaker.

19. 6. Pour the extracting solution on the mash strawberry and place the beaker in a water bath with water at 60°C.Assure to mix the mash strawberry so to distribute the extracting solution and to make the temperature uniform for 15 minute 7. After 15 minutes, place the beaker in the water with ice cubes and mix the mash strawberry to make the temperature uniform for 5 minute.

20. 8. After 5 minutes, remove the beaker from the cold water and prepare for filtration. 9. Place the sieve on the different beaker, take a filter paper, soak it and place it in the sieve. 10. Pour a little pulp on the filter. Mix with care to help the filtration and avoid ripping the filter paper.

21. With this additional operation it is possible to obtain a purer DNA extract, but it it is not essential if you want to observe the DNA. Because DNA is wrapped on proteins called histones is will be necessary to remove these proteins to obtain a DNA extract of higher purity. To remove these histones, you can use proteolytic enzymes like Protease. While you can purchase protease in a shop that sells chemical products, you can also substitute it with a substance that is much easier to find; it is found in the juice of the pineapple which that contains Bromelain, a substance able to breakdown proteins into the amino acids of which they are composed. 11. In a tube, pour 5 cm3 of the filtered solution and add 1 cm3 of pineapple juice and mix it and wait 2 - 3 minutes to let to the bromelain react.

22. 12. Slowly, pour in the tube of the previous step some icy alcohol by avoiding it mix with the filtrate. 13. Add the volume of the alcohol has to be about the same of that of the solution. 14. let the tube rest for 5 minutes to allow to the DNA to precipitate and accumulate in the tube. 15. Step 1 to 14 is repeated by changing it to 6g, 9g, 12g of salt in the buffer solution.

23. Expected observation

24. THE END