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THE HISTORY OF DNA

FRIEDRICH MIESCHER (1869) Discovered a nonprotein substance in the nuclei of pus cells Named the substance “nuclein”. THE HISTORY OF DNA. Joachim Hammerling (1930’s)

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THE HISTORY OF DNA

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  1. FRIEDRICH MIESCHER (1869) Discovered a nonprotein substance in the nuclei of pus cells Named the substance “nuclein” THE HISTORY OF DNA

  2. Joachim Hammerling (1930’s) Experiments with the green algae Acetabularia showed that the regeneration of appendages required the nucleus which was located in the foot Suggested that genetic information is stored in the nucleus

  3. Erwin Chargaff (1949) Chemical analysis showed that: A = T and G = C A + G = T + C Complementary base-pairing

  4. Alfred Hershey and Martha Chase (1952)

  5. Their experiments showed that DNA tagged with radioactive phosphorus (32P) was found inside infected bacterial cells and directed the synthesis of new viral DNA and new viral protein coats • Protein coats tagged with radioactive sulfur (35S) did not enter bacterial cells • Suggested that DNA is the hereditary material

  6. Rosalind Franklin (1953) X-ray diffraction showed that DNA was in the shape of a double helix

  7. Watson and Crick (1953)

  8. Watson and Crick deduced the model of DNA that persists today: • Double helix, clockwise (right-handed helix) • 1 complete turn every 10 nucleotides (3.4 nm full helical twist) • Sugar-phosophate backbone • Complementary base-pairing between nucleotides – hydrogen bonding • Constant diameter of 2nm • Antiparallel strands

  9. DNA STRUCTURE

  10. Composed of nucleotides held together by phosphodiester bonds Each nucleotide consists of a deoxyribose sugar, a phosphate group and a nitrogenous base The Chemical Composition of DNA

  11. Deoxyribose sugar

  12. Pyrimidines (single rings) Thymine Cytosine Purines (double rings) Adenine Guanine 4 Nitrogenous Bases

  13. Phosphodiester bonds hold the sugar-phosophate backbone together Each DNA strand has a 5’ end (attached to a phosphate group) and a 3’ end (attached to a hydroxyl group) Sugar-Phosphate backbone

  14. Hydrogen bonding occurs between complementary base pairs.

  15. DNA is a double helix The two strands run “antiparallel” to one another Hydrogen bonds hold the complementary bases together DNA Molecule

  16. Writing DNA sequences: Every DNA molecule has “directionality” and bases sequences are written as follows: e.g.) 5’ – ATGCCGTTA – 3’ 3’ - TACGGCAAT – 5” (Usually, only the 5’ to 3’ strand is written since the complementary strand can be deduced.)

  17. What attributes of DNA’s structure enable it to be replicated? • Complementary base-pairing • Hydrogen bonds between base pairs • Double stranded, therefore, each strand can serve as template for the replication of the complementary strand

  18. Gene Organization and Chromosome Structure

  19. Define These Terms • Gene • Chromosome • Histone • Chromatin • Metaphase chromosome • Chromatid • Centromere

  20. Gene – a sequence of nucleotides that codes for a protein • Chromosome – one continuous double-stranded DNA molecule • Histone – a positively charged protein that binds to negatively charged DNA • Chromatin – complex of DNA and histones located in the nucleus of eukaryotic cells • Metaphase chromosome – a duplicated chromosome • Chromatid – one half of a duplicated chromosome • Centromere – a constricted region that holds two replicated chromosomes together

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