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DNA

Chapter 4 – Biology 12 textbook. DNA. Molecule of Life. DNA. Deoxyribonucleic Acid. DNA contains all the information for the formation of an organism Chromosomes – are made of condensed DNA

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DNA

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  1. Chapter 4 – Biology 12 textbook DNA Molecule of Life

  2. DNA... Deoxyribonucleic Acid

  3. DNA contains all the information for the formation of an organism • Chromosomes – are made of condensed DNA • DNA controls the production of proteins – which form the structure of the cell & control chemical reactions

  4. Gregor Mendel – 1865Father of Genetics • Discovered that organisms pass their characteristics to their offspring • Also: genes are found in pairs • Using experiments with pea plants, he determined the laws of inheritance – without knowing anything about DNA

  5. Friedrich Miescher – 1871Isolation of DNA • Isolated DNA for the 1st time – found in the nucleus • Called it “nuclein” • Did not realize that it was genetic information • DNA = carbon, hydrogen, oxygen, nitrogen & phosphorous

  6. Other scientists improved DNA extraction & found that DNA is an acidic long chain molecule (polymer) made of nucleotides • 1 nucleotide: • Pentose sugar • Phosphate group • Nitrogenous base Nucleotide

  7. Sugar-phosphate Backbone • 2 components of the backbone: • Pentose sugar: deoxyribose • Phosphate group: phosphoric acid

  8. Deoxyribose sugar • 5 carbons • Carbons are numbered clockwise 1’ – 5’ (1 prime to 5 prime) • 3’ & 5’ carbons links to phosphate groups with ester bonds • 1’ carbon links to the nitrogenous base with a glycosyl bond

  9. Phosphate group • Negatively charged • Free Oxygen links to the sugar

  10. 4 Nitrogenous Bases • Adenine • Guanine • Thymine • Cytosine

  11. Purines  double ringed molecules: • Adenine • Guanine • Pyrimidines  single ringed molecules • Thymine • Cytosine

  12. Phoebus Levine discovered that each of the nitrogenous bases is attached to the sugar & the sugar is attached to the phosphate group • These 3 components make up nucleotides

  13. Nucleotide structure

  14. Watson & Crick • In 1953, thanks to an X-ray image by Rosalind Franklin, Watson & Crick discovered that DNA is in the form of a spiral • Called a double helix

  15. An unrolled helix looks like a ladder • The sugar phosphate backbone forms the 2 sides • The nitrogenous bases form the rungs • The bases are linked to each other with hydrogen bonds

  16. In a molecule of DNA, the quantities of adenine & thymine are equal & guanine = cytosine • Watson & Crick found that the structure of the bases determines which other base they bond with • Complimentary bases are: • A & T • G & C

  17. Hydrogen bonds link complimentary bases • The 2 strands are complimentary & antiparallel • One strand runs 3’- 5’, the other strand runs 5’ – 3’

  18. If you know the sequence of one strand, you also know the sequence of the other strand 5’ – TCGAATTGCGCGATA – 3’ 3’ - _________________ - 5’ • Purines bond with pyrimidines so the diameter of DNA is a constant 2nm • DNA is twisted clockwise – “right-handed helix” • One complete turn (3.4 nm) every 10 nucleotides

  19. Hydrogen bonds: individually weak, collectively strong • 3 H bonds between G & C • 2 H bonds between A & T • G cannot bond with T & A cannot bond with C because the molecule would be unstable – too few H bonds

  20. Homework questions: Page 216 #1-10

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