L12. DNA EXTRACTION

L12. DNA extraction

1. Introduction

Deoxyribonucleic acid (DNA) is a nucleic acid that encodes the genetic instructions used in the development and functioning of all known living organisms and many viruses.
Nucleic acid are biopolymers formed by simple units called nucleotides. Each nucleotide is composed of a nitrogen - containing nucleobase ( G, T,C,A) as well as a monosaccharide and a phosphate group.

These nucleotides are joined to one another in a chain by covalent bonds between the sugar of one nucleotide and the phosphate of the next. Most DNA molecules consist of two strands coiled around each other to form a diuble helix. Hydrogen bonds bind the nitrogenous bases of the two separate strands.

The two strands run in opposite directions to each other and are therefore anti-patallel. Moreover the bases of the two opposite strands unit according to base pairing rules: A-T and C-G.

Within cells, DNA is organized into structures called chromosomes.

2. Objectives

• Study DNA structure
• Understand the process of extracting DNA from a tissue.

3. Material

• 1L Erlenmeyer flask
• 100mL beaker
• 10mL graduated cylinder
• Small funnel
• Glass stirring rod
• 10mL Pipet
• Knife
• Safety goggles
• Cheesecloth
• Kiwi
• Pineapple juice
• Distilled water
• 90% Ethanol ice-cold
• 7mL DNA buffer
• 50mL dish soap
• 15g NaCl
• 900mL tap water

4. Procedure

Prepare the buffer in a 0,5L beaker: Add 450mL of tap water, 25mL of dish soap and 7g NaCl. Stir the mixture.

First of all peel the kiwi and chop it to small pieces and place the pieces of the kiwi in one 600mL beaker and smash with a fork until it becomes a juice puree.

Add 8mL of buffer tot he mortar and mash the kiwi puree carefully for 1 minute without creating many bubbles. Filter the mixture: put the funnel on top of the graduated cylinder. Place the cheesecloth on top of the funnel.

After, add beaker containq carefully on top of the cheesecloth to fill the graduated cylinder. The juice will drain through the chessecloth but the chucks of kiwi will not pass through into the graduated cylinder.

Add the pineapple juice to the green juice. This step will help us to obtain a purer solution of DNA, Pineapple juice contains an enzyme that breaks down proteins.

Tilt the graduated cylinder and pour in an equal amount of ethanol with an automatic pipet. Put the ethanol through the sides of the graduated cylinder very carefully. You will need about equal volumes of DNA solution to ethanol.

Place the graduated cylinder so that it is eye level. Using the tirring rod, collect DNA at the boundary of ethanol and kiwi juice. Do not stir the kiwi juice.

The DNA precipitate looks like long, white and thin fibers,

Finally, gently remove the stirring rod and examine what the DNA looks like.

5. Observations

We can observe the fibers of the DNA.

6. Questions

1. What did the DNA looks like?

DNA was placed in the top part floating in ethanol was.

2. Why do you mash the DNA? Where it is located inside the cells?

The crush to extract the liquid from the kiwi, the DNA is in the nucleus of cells.

3. DNA is soluble in water, but not in ethanol. What does this fact have to do with our method of extraction?

DNA because the floats in ethanol therefore we can observe as it does not dissolve.