7.1 DNA Structure PDF

Topic 7.1: DnA STRuCTuRE Genetic Material Hershey and Chase conducted experiments in 1952 to determine if DNA or proteins were the genetic material of a cell It was previously known that viruses insert their genetic material into cells and so radioactively labeled viruses were prepared Viruses g...

Topic 7.1: DnA STRuCTuRE Genetic Material Hershey and Chase conducted experiments in 1952 to determine if DNA or proteins were the genetic material of a cell It was previously known that viruses insert their genetic material into cells and so radioactively labeled viruses were prepared Viruses grown in 35S had radioactive proteins but did not transfer this radioactivity to bacterium (remained in supernatant) Viruses grown in 32P had radioactive DNA and did transfer this radioactivity to infected bacterium (found in pellet) Experiment 1: Testing Protein with 35S Experiment 2: Testing DNA with 32P 300 300 Protein Radioactive DNA Radioactive Infection Centrifuge labelled Infection Centrifuge pellet labelled supernatant Conclusion: Proteins not genetic material Conclusion: DNA is the genetic material X-ray Diffraction Franklin and Wilkins used X-ray diffraction to elucidate DNA structure X-rays will diffract when targeted at crystallised DNA molecules The scattering pattern created can be used to determine structure From the patterns generated, the following properties were deduced: Wilkins Composition: DNA is a double-stranded molecule Orientation: The bases face inwards and the phosphates face out Shape: DNA forms a double helix (10 bases per twist) Wilkins Diffraction Franklin Nucleosomes Non-Coding DNA In eukaryotes, DNA associates with eight Some regions of DNA do not code for protein DNA H1 histone proteins to form a nucleosome Satellite DNA (tandem repeats) Telomeres (chromosome ends) Nucleosomes help to supercoil the DNA Introns (non-coding sequences) Makes DNA compact (better storage) Prevents DNA damage (less exposed) Non-coding RNA genes Gene regulatory sequences Assists in cell division (more mobility) Involved in transcriptional regulation Histones (octamer) Tandem repeats are used in DNA profiling Eukaryotic Organisation of DNA DNA is bound with histone proteins to form nucleosomes that are then linked together to form strings of chromatosomes These coil to form solenoids, which condense into 30 nm fibres, before being compressed and folded into chromatin DNA Nucleosome Chromatosome Solenoid 30 nm fibre Chromatin Chromosome