Home > Biology > Extracting DNA

Extracting DNA

By: Suzanne Elvidge BSc (hons), MSc - Updated: 28 Sep 2012 |
 
Dna Deoxyribonucleic Acid Genetic

DNA (deoxyribonucleic acid) is the molecule that carries the genetic information (the instructions) for the cell, and DNA is found in all cells that have a nucleus. DNA is made of two chains of molecules known as nucleotides. The nucleotides in one chain link to the nucleotides in the other in pairs, and the two chains twist around each other in a spiral known as a double helix.

The nucleotides are called adenine (A), thymine (T), cytosine (C) and guanine (G). Adenine always pairs with thymine and cytosine always pairs with guanine. The genetic information in DNA is coded by these nucleotides – they form three letter ‘words’, and each word is a code for an amino acid. Amino acids are the building blocks for proteins, which make up all living things. A gene is a sequence of nucleotides that codes for a particular characteristic in an organism.

Extracting DNA

Cool down some methylated spirits by putting the bottle in a bowl and surround it with ice cubes. Measure out 900 ml of water, and gently stir in 25 g of salt and 80 g of washing up liquid (cheap, non-concentrated washing up liquid seems to work the best), without making too many bubbles. Peel the kiwi fruit, chop it and then put it in a small bowl and mash it with a fork. Pour in 100 ml of the salt and detergent mixture, stir, and put the bowl in a pan of hot (not boiling water). Leave this for 15 minutes, and then strain it through a sieve into a glass.

Carefully pour in an equal amount of cold methylated spirits, slowly dripping it down the side of the glass so that it forms a layer on top of the kiwi fruit paste. A white layer should form between the methylated spirit and the kiwi fruit paste – this is DNA.

The mashing, and then the salt and detergent break open the cells. Kiwi fruit contain enzymes called proteases. These break down the proteins in the nucleus that keep the DNA packed tightly together. DNA dissolves in water but does not dissolve in alcohol, so forms a layer between the kiwi fruit paste, which contains water, and the methylated spirits, which contains alcohol. Try it with an onion or pineapple – these also contain proteases.

Do All Cells Contain DNA?

The only cells in the human body that do not contain DNA are the red blood cells. The cells have a nucleus in the early stages, but lose these later so that they can carry more haemoglobin, which carries oxygen around the body.

DNA Fingerprints

A DNA fingerprint is a profile of a person’s DNA, and almost everyone’s DNA fingerprint is different (the only people will identical DNA fingerprints are identical twins). The police can use DNA fingerprints to identify people who have committed crimes, if they have left any samples of their DNA behind, such as hair or blood. They are also used to research and diagnose disease, and to identify the biological parents of children.

You might also like...
Share Your Story, Join the Discussion or Seek Advice..
Why not be the first to leave a comment for discussion, ask for advice or share your story...

If you'd like to ask a question one of our experts (workload permitting) or a helpful reader hopefully can help you... We also love comments and interesting stories

Title:
(never shown)
Firstname:
(never shown)
Surname:
(never shown)
Email:
(never shown)
Nickname:
(shown)
Comment:
Validate:
Enter word:
Topics
Latest Comments
  • Mosey Cook
    Re: Make Yoghurt and Grow Yeast
    This article on natural yeast and good bacteria has been the best read I’ve read on the Internet
    1 November 2019
  • Tee
    Re: Vibrations: Seeing and Feeling Sound
    I have just witnessed a fork vibrating so fast on its own on the kitchen top. It made a sound while vibrating as if the…
    24 August 2019
  • simran panaich
    Re: Soap and Detergent Chemistry
    thnx!! It helped me a lot !!! THank YOu so much
    6 June 2019
  • Mar2
    Re: Why Oil and Water Don't Mix
    I am doing this as a demo for homogeneous mixture examples. It really helps, it is interesting, and thank you so much for it!!!
    5 June 2019
  • COOL STUDENT
    Re: Why Oil and Water Don't Mix
    Why does the food coloring mix with the water i did not quite get iy
    31 May 2019
  • EMILY BAKER
    Re: Looking at Soil Profiles
    This thing is stupid. I am a doctor and I know better then you do! I will do something about this website if you don’t change the…
    25 May 2019
  • Alice Picello
    Re: Looking at Soil Profiles
    THIS DIDN’T TEACH ME ANYTHING ON SOIL PROFILES
    25 May 2019
  • Rea
    Re: Making an Emulsion
    I have always wondered about the Earth. My teacher gave us this website to read about why water and oil don't mix. I started looking around on…
    16 May 2019
  • Candytashy
    Re: Looking at Soil Profiles
    Thanks so much for this post .it really helped me .made my homework much easier and l have learnt a lot from this post
    25 March 2019
  • Rajput
    Re: Pulling and Pushing: Magnetic Attraction
    Kya kisi chemical ko copper me mix karne se iron or steel ko push kiya ja sakte hai. Yadi ho to formula batye.
    25 March 2019