Dna Extraction from onions

Practical 2 – DNA Extraction from Onions

Title

DNA Extraction from onions.

Hypothesis

The strands of DNA from the onions can be seen floating on the top layer of the mixture and is extracted successfully.

Aim

 To extract the DNA from onion samples.

Introduction

 DNA is a nucleic acid located in the cell's nucleus. It is found making up the genetic material and is bound to several types of proteins. DNA is a molecule made up of two complementary strands that are wound around each other in a double helix. Within the relatively simple double helix structure, DNA holds the coded information for how to make every protein a living organism might need throughout its entire life.

The extraction of DNA from a cell is often a first step for scientists who need to obtain and study a gene. The total cell DNA is used as a pattern to make copies (called clones) of a particular gene. These copies can then be separated away from the total cell DNA, and used to study the function of that individual gene.

Once the gene has been studied, genomic DNA taken from a person might be used to diagnose him or her with a genetic disease. Alternatively, genomic DNA might be used to mass produce a gene or protein important for treating a disease. This last application requires techniques that are referred to as recombinant DNA technology or genetic engineering.

Materials

Salt, Onions, knives, kitchen blender, beakers, liquid detergent, warm water bath (55®C), strainers, cheese cloth, boiling tubes, ice, ice cold ethanol, forceps/plastic forks

Procedure

1. 2 spoons of salt are dissolved in 200ml of water.
2. Two onions are peeled and cut into smaller sized chunks and the layers are separated out.
3. Onion pieces and salt water are placed in a blender and is blended 3 times at 5 seconds each.
4. The lumpy onion mixture is poured into a beaker.
5. 10 spoons of liquid detergent are added and is stirred gently.
6. The mixture is incubated in a warm water bath (55°C) for 5 minutes.
7. A strainer is lined with a cheese cloth.
8. The mixture is strained into a beaker.
9. The filtrate is transferred into a beaker.
10. The boiling tube is placed in an ice water bath, and is swirled gently for 5 minutes.
11. The boiling tube is tilted at a slant and an equal amount of ice cold ethanol is poured carefully down the side of the boiling tube so a layer is formed on top of the onion-salt-soap mixture.
12. The solution is sat for 5 minutes without disturbing it.
13. A pair of forceps/plastic fork is used and the strands of DNA is lifted out gently from the mixture.

Discussion

1. Discuss the outcome of the experiment:

There are three main steps in DNA extraction which are homogenization, deproteinization and precipitation of DNA. The onion was cut into pieces and poured into a blender with salt water. The salt shields the negative phosphate end of DNA which allows these ends to come closer so they can precipitate out of a cold alcohol solution. By blending the onion, the cell walls, plasma membranes, and the nuclei material were broken down, so the DNA in the onion can be released. Detergent was added after blending the onion as the solution causes the cell membrane to break down by disrupting the polar interaction that hold the cell membrane together.

After adding the detergent solution, the mixture in the beaker was placed in a warm water bath. This helps to soften the onion tissues and allow penetration of the homogenization solution. It also denatures many enzymes that may denature the DNA . the mixture was then strained into a beaker to remove bigger debris such as cell walls, membranes and others. The filtrate in the boiling tube was then placed in an ice water bath to prevent the denaturation of DNA.

An equal amount of ice-cold ethanol was poured into the boiling tube so that it prevents the DNA strands from breaking apart. Two layers were formed in the boiling tube. When the precipitation is completed, the liquid within the boiling tube becomes cloudy. DNA is insoluble in ice-cold ethanol , hence DNA form the upper layer. It forms a precipitate which is thick, stringy, white mass on the top layer of the solution.