25 ch03nucleicacids2008


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  • Isn’t this a great illustration!?
  • DNA & RNA are negatively charged: Don’t cross membranes. Contain DNA within nucleus Need help transporting mRNA across nuclear envelope. Also use this property in gel electrophoresis.
  • The 2 strands are complementary. One becomes the template of the other & each can be a template to recreate the whole molecule.
  • H bonds = biology’s weak bond • easy to unzip double helix for replication and then re-zip for storage • easy to unzip to “read” gene and then re-zip for storage
  • when cells divide, they must duplicate DNA exactly for the new “daughter” cells Why is this a good system?
  • when cells divide, they must duplicate DNA exactly for the new “daughter” cells Why is this a good system?
  • The greatest understatement in biology!
  • Discovered & published in 1953 Nobel Prize in 1962: Watson, Crick, Wilkins
  • A chemist by training, Franklin had made original and essential contributions to the understanding of the structure of graphite and other carbon compounds even before her appointment to King's College. Unfortunately, her reputation did not precede her. James Watson's unflattering portrayal of Franklin in his account of the discovery of DNA's structure, entitled "The Double Helix," depicts Franklin as an underling of Maurice Wilkins, when in fact Wilkins and Franklin were peers in the Randall laboratory. And it was Franklin alone whom Randall had given the task of elucidating DNA's structure. The technique with which Rosalind Franklin set out to do this is called X-ray crystallography. With this technique, the locations of atoms in any crystal can be precisely mapped by looking at the image of the crystal under an X-ray beam. By the early 1950s, scientists were just learning how to use this technique to study biological molecules. Rosalind Franklin applied her chemist's expertise to the unwieldy DNA molecule. After complicated analysis, she discovered (and was the first to state) that the sugar-phosphate backbone of DNA lies on the outside of the molecule. She also elucidated the basic helical structure of the molecule. After Randall presented Franklin's data and her unpublished conclusions at a routine seminar, her work was provided - without Randall's knowledge - to her competitors at Cambridge University, Watson and Crick. The scientists used her data and that of other scientists to build their ultimately correct and detailed description of DNA's structure in 1953. Franklin was not bitter, but pleased, and set out to publish a corroborating report of the Watson-Crick model. Her career was eventually cut short by illness. It is a tremendous shame that Franklin did not receive due credit for her essential role in this discovery, either during her lifetime or after her untimely death at age 37 due to cancer.
  • At the foundation of biology is chemistry!!
  • All other biomolecules we spoke about served physical or chemical functions. DNA & RNA are information storage molecules. DNA well-suited for an information storage molecule: chemically stable stores information in the varying sequence of nucleotides (the genetic code) its coded sequence can be copied exactly by the synthesis of complementary strands; easily unzipped & re-zipped without damage (weak H bonds) damage to one strand can be repaired by addition of bases that match the complementary strand
  • 25 ch03nucleicacids2008

    1. 1. 2006-2007AP Biology Nucleic acids
    2. 2. 2006-2007AP Biology Nucleic Acids Information storage
    3. 3. AP Biologyproteinsproteins DNADNA Nucleic Acids  Function:  genetic material  stores information genes blueprint for building proteins  DNA → RNA → proteins  transfers information blueprint for new cells blueprint for next generation
    4. 4. AP Biology A A A A T C G C G T G C T
    5. 5. AP Biology Nucleic Acids  Examples:  RNA (ribonucleic acid)  single helix  DNA (deoxyribonucleic acid)  double helix  Structure:  monomers = nucleotides RNADNA
    6. 6. AP Biology Nucleotides  3 parts  nitrogen base (C-N ring)  pentose sugar (5C)  ribose in RNA  deoxyribose in DNA  phosphate (PO4) group Are nucleic acids charged molecules? Nitrogen base I’m the A,T,C,G or U part!
    7. 7. AP Biology Types of nucleotides  2 types of nucleotides  different nitrogen bases  purines  double ring N base  adenine (A)  guanine (G)  pyrimidines  single ring N base  cytosine (C)  thymine (T)  uracil (U) Purine = AG Pure silver!
    8. 8. AP Biology Nucleic polymer  Backbone  sugar to PO4 bond  phosphodiester bond  new base added to sugar of previous base  polymer grows in one direction  N bases hang off the sugar-phosphate backbone Dangling bases? Why is this important?
    9. 9. AP Biology Pairing of nucleotides  Nucleotides bond between DNA strands  H bonds  purine :: pyrimidine  A :: T  2 H bonds  G :: C  3 H bonds Matching bases? Why is this important?
    10. 10. AP Biology DNA molecule  Double helix  H bonds between bases join the 2 strands  A :: T  C :: G H bonds? Why is this important?
    11. 11. AP Biology Copying DNA  Replication  2 strands of DNA helix are complementary  have one, can build other  have one, can rebuild the whole Matching halves? Why is this a good system?
    12. 12. AP Biology When does a cell copy DNA?  When in the life of a cell does DNA have to be copied?  cell reproduction  mitosis  gamete production  meiosis
    13. 13. AP Biology DNA replication “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.” James Watson Francis Crick 1953
    14. 14. AP Biology Watson and Crick … and others… 1953 | 1962
    15. 15. AP Biology Maurice Wilkins… and… 1953 | 1962
    16. 16. AP Biology Rosalind Franklin (1920-1958)
    17. 17. AP Biology Interesting note…  Ratio of A-T::G-C affects stability of DNA molecule  2 H bonds vs. 3 H bonds  biotech procedures  more G-C = need higher T° to separate strands  high T° organisms  many G-C  parasites  many A-T (don’t know why)
    18. 18. AP Biology Another interesting note…  ATP Adenosine triphosphate ++  modified nucleotide  adenine (AMP) + Pi + Pi
    20. 20. 2006-2007AP Biology Macromolecule Review
    21. 21. AP Biology Carbohydrates  Structure / monomer  monosaccharide  Function  energy  raw materials  energy storage  structural compounds  Examples  glucose, starch, cellulose, glycogen glycosidic bond
    22. 22. AP Biology Lipids  Structure / building block  glycerol, fatty acid, cholesterol, H-C chains  Function  energy storage  membranes  hormones  Examples  fat, phospholipids, steroids ester bond (in a fat)
    23. 23. AP Biology Proteins  Structure / monomer  amino acids  levels of structure  Function  enzymes defense  transport structure  signals receptors  Examples  digestive enzymes, membrane channels, insulin hormone, actin peptide bond
    24. 24. AP Biology Nucleic acids  Structure / monomer  nucleotide  Function  information storage & transfer  Examples  DNA, RNA phosphodiester bond
    25. 25. AP Biology Let’s build some DNA, baby!
    26. 26. 2007-2008AP Biology Ghosts of Lectures Past (storage)
    27. 27. AP Biology Building the polymer
    28. 28. AP Biology RNA & DNA  RNA  single nucleotide chain  DNA  double nucleotide chain  N bases bond in pairs across chains  spiraled in a double helix  double helix 1st proposed as structure of DNA in 1953 by James Watson & Francis Crick (just celebrated 50th anniversary in 2003!)
    29. 29. AP Biology Information polymer  Function  series of bases encodes information  like the letters of a book  stored information is passed from parent to offspring  need to copy accurately  stored information = genes  genetic information Passing on information? Why is this important?