In this IBDP Biology Blog post, we will find out the important figures who aid to discover the parts of genetic materials within our DNA.
Sanger - Base Sequencing in DNA
- Dideoxyribose have no OH group on carbon atom 3
- If a dideoxynucleotide is at the end of a strand of DNA: NO site to which another nucleotide can be added by a 5' to 3' linkage
1. In sequencing machine single-stranded copies of the DNA being sequenced are mixed with
- DNA Polymerase
- Normal DNA nucleotides
- Small numbers of ddna nucleotides
Replication is repeated four times: Once with dideoxyribosenucleotides with each base A T C G
Results: Fragments of DNA vary in length - depending on how far replication got before it was terminated because a ddNA nucleotide was added to the end of the chain Hershey and Chase Experiment - Genetic Material
2. Fragments were seperated according to length by Gel Electrophoresis with four tracks
- One for each base in the DNA nucleotide that terminated replication
- Each band in gel repersents one length of DNA fragment produced by replication
- All fragments of same length end in same base
- A band in one of the four tracks for each length of fragment
The whole base sequence can easily be deduced. Fluorescent markers allowed the base sequence to be read by a machine.
- Dideoxyribosenucleic acid stops DNA Replication when it is added to a new DNA strand
- Fluroscent dye markers are attached to dideoxyribosenucleic acids so that the base present when replication stops can be identified. The base on the parent strand can be deduced
- New strands of different lengths are produced
- The length of a strand and base are identified by sequencing machines
Franklin and Wilkins investigation - Structure of DNA
What is the structure of DNA [look like]?
Rosalind Franklin and Maurice Wilkins investigated the structure of DNA using X-Ray Diffraction
X-Ray Diffraction: When X-Rays are directed at a material some is scattered by the material. This scattering is known as diffraction
For X-Ray Diffraction to be successful:
- Material should be crystalized [crystals remain undistured while cooling - grow according to a regular pattern]
So that the repeating pattern causes diffraction to occur in a regular way
DNA cannot be crystalized but molecules arranged regularly enough for technique to work
Atoms, molecules or ions that make up solids can be arranged in an orderly, repeating pattern
That's all! Good Job!
References:
- https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.thermofisher.com%2Fblog%2Fbehindthebench%2Fhow-does-sanger-sequencing-work%2F&psig=AOvVaw3c7IShCuYwYJCIjQiAZDkq&ust=1626201011406000&source=images&cd=vfe&ved=0CAoQjRxqFwoTCNDR8_-U3vECFQAAAAAdAAAAABAD
- https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.sciencehistory.org%2Fhistorical-profile%2Fjames-watson-francis-crick-maurice-wilkins-and-rosalind-franklin&psig=AOvVaw3Vj3BPHG23G1Y_uXUJRk4b&ust=1626201075911000&source=images&cd=vfe&ved=0CAoQjRxqFwoTCLii0p6V3vECFQAAAAAdAAAAABAJ
Drafted by Venetia (Biology)