DNA as Genetic Information

  • Created by: rosieevie
  • Created on: 02-01-17 14:28

DNA is the Genetic Material

  • Avery 1944
  • Utilised fractionation techniques to purify DNA and transformation was unaffected by protease/RNAse
  • DNA was destroyed by DNAse and the mouse stayed alive, suggesting that DNA was the genetic material


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  • Small and simple (2um)
  • 70s ribosomes
  • Non-membrane bound DNA
  • Plasmids - small circular DNA
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Types of Genetic Mutations

Missense mutation - change in base pair results in codon for a different amino acid

Nonsense mutation - change in base pair results in a protein chain-terminating codon

Insertion mutation - adding extra base pairs resulting in change in base number

Deletion mutation - removing sections of DNA

Substitution mutation - exchanges one base for another

Duplication mutation - a piece of DNA abnormally copied 1 or more times

Frameshift mutation - when insertion/deletion alters the gene so codons are changed

Repeat expansion mutation - increases the amount of times that a codon is repeated

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DNA is the Genetic Material

Griffth 1928

  • Smooth Pneumococcus bacteria is resistant to mouse immune system
  • Rough Pneumococcus bacteria lacks the resistant coat
  • Indicated information was passed on from dead type to live type = transforming principle


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  • Nucleus containing DNA
  • Membrane-bound organelles
  • 20um diameter (larger)
  • 80s ribosomes
  • Chromosomes hold DNA
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Genetic Diseases

Downs Syndrome - 3 copies of chromosomes 21 (often from older mothers)

Turner Syndrome - woman with 1 X chromosome (monosomy) = infertile, short

Klinefeller Syndrome - man with 1 Y and 2 X chromosomes (trisomy) 

Non-disjunction - failure of homologous chromosomes or sister chromatids to separate during gamete formation

Philadelphia Chromosome - translocation in bone marrow causes permenant switch on = cancer

Cystic Fibrosis - recessive mutation causing a deletion in CFTR channel gene = sticky mucus

Sickle-cell Disease - mutation from A to T in beta haemoglobin chain = anemia, pain, infection

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Chromosome - a protein and DNA complex containing all/part of genome


Diploid cells - cell with 2 equivalent sets of chromosomes e.g. epithelial

Haploid cells - cell with one set of unique chromosomes e.g. gametes

Homologous chromosomes - pair of chromosomes with same genes (maybe different alleles)

Chromatin - the DNA/protein complex folded into a compact structure

Karyotype - number and visual appearance of full set of chromosomes

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DNA is the Genetic Material

Hershy and Chase 1952

  • 1 bacteriophage labelled with radioactive sulphur in protein coat (DNA has no sulphur)
  • 1 bacteriophage labelled with radioactive phosphorous - incorperated into DNA
  • Phage DNA entered bacterial cells but not proteins - DNA genetic material
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Visualising Chromosomes - dyes (G-banding)

Dark parts (less):

  • AT-rich
  • More condensed
  • Less transcriptionally active


Light parts (more)

  • GC-rich
  • Less condensed
  • More transcriptionally active


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First Discovery of DNA

Miescher 1869:

  • Protein function study of pus
  • Cell cytoplasm from white blood cells
  • Add acid = white precipitate
  • Rich in phosphorous but no sulphur (not protein)
  • Nuclein now called DNA
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