BIOL 450: Modern Genetics (Module 1 Lecture 1 & 2- Chap. 7: DNA Structure & Replication)

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BIOL 450: Modern Genetics (Module 1 Lecture 1 & 2- Chap. 7: DNA Structure & Replication)
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BIOL 450: Modern Genetics (Module 1 Lecture 1 & 2- Chap. 7: DNA Structure & Replication)
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  1. Nature of Biological Information
    • - Organisms develop from a single cell that contains information specifying steps of development and biological properties of that organism
    • - Organism made of trillions of cells -> each cell has a nucleus with 2 copies of chromosomes -> chromosome pair -> each chromosome is a long DNA strand with functional regions called genes -> DNA is a double helix
  2. Chromosome
    • - 2 pairs of chromosomes in each nucleus
    • - each copy is the genome
  3. How did we figure out that DNA is genetic material?
    • - Needed to determine what are the cellular macromolecules (carbs, lipids, proteins, nucleic acids: DNA & RNA)
    • - Whicch is the hereditary material?
    • - Determined by Avery's experiment with Diplococcus pneumoniae (1944)
  4. What was known in the early 1940s?
    • - Genes are associated with specific traits (mutations alter gene function, but how?)
    • - Genes are protein structures
    • - Genes are on chromosomes
    • - Chromosomes consist of DNA and protein
  5. What was Griffith's experiment in 1928?
    • - Used Diplococcus pneumoniae and mice
    • - Used 2 strains:
    •    - Smooth colonies which are "hidden" from immune system and are virulent (mouse dies)
    •    - Rough colonies which are not "hidden" so are avirulent (mouse lives)
    • - Observation:
    •    - If S-strain is heat-killed then injected, mouse lives
    •    - If S-strain is heat-killed but contains transforming factor that can convert non-virulent (R-strain) to lethal form and then both are injected, mouse dies
    • - Hypothesis: what chemical component is the transformming factor
  6. How would you test Griffith's hypothesis?
    -
  7. What was Avery's experiment (1944)?
    • - Using Diplococcus pneumoniae and mice, he tested Griffith's hypothesis: If he destroys the transforming factor in the heat-killed virulent cells, then it will not transform the live avirulent cells
    • - Method:
    •    - Treat extract of heat-killed virulent (S) cells
    •    - Mix treated extract with avirulent (R) cells
    •    - Inject into mice
    • - 6 treatments: control than either polysaccharides, lipids, RNA, proteins or DNA destroyed
  8. What was the results of Avery's experiment (1944)?
    • - The transforming factor is destroyed when the S-strain extract is treated with DNAse
    • - Conclusion: the transforming factor is made of DNA
  9. What was the Hershey-Chase experiment?
    • - Studies viruses that infect bacteria
    • - Hypothesis: if they label viral DNA and proteins with different radioisotopes, the genetic material will carry only that label into the bacterial cells (DNA contains phosphorus, the proteins contain sulfur)
    • - Experiment outline
    •    - Grow 1 batch of virus in radioactive S-35 (label proteins)
    •    - Grow 1 batch of virus in radioactive P-32 (label DNA)
  10. What was the results of the Hershey-Chase experiment?
    • - S-35 labeled viral proteins were found outside the bacterial cells
    • - P-32 labeled viral DNA was found insidde the bacterial cellls
    • - Conclusion: DNA is genetic material in virus
  11. 3 key properties of DNA
    • - Faithful repliication
    • - Informational content (encodes proteins)
    • - Mostly stable, but mutable
  12. What 2 empirical rules did Chargaff establish?
    • - Amount of A = amount of T and amount of G = amount of C
    • - Amount of (A plus G) = amount of (C plus T)
  13. What critical experimental result did Rosalind Franklin find?
    • - She was first to photograph DNA in its natural state
    • - Important insights:
    •    - DNA is helix
    •    - Backbonne is on outside
    •    - Diameter 2nm
    •    - Repeat every 0.34 nm and 34nm
  14. Who put together the first model of DNA?
    • - Watson and Crick
    • - They were supposed to be studying proteins
    • - They put Chargoff's numbers and Franklins structural data together
  15. Primary structure of DNA
    • - Nucleotides are the building blocks (monomers) of the DNA polymer
    • - Each nucleotide is composed of 3 chemical groups:
    •    - 5 carbon sugar (deoxyribose)
    •    - Phosphte group(s) (1-3 linked to each other)
    •    - 1 nitrogen base (4 possible)
  16. Structure of the ribose sugar
    • - 1'C: attachment site for nitrogen base
    • - 2'C: OH attachment- sugar is a ribose (RNA); H attached- sugar is deoxyribose (DNA)
    • - 5'C: O is attachment site for phosphate group
    • - 3'C: O is attachment site for phosphate group from next nucleotide when polymerizin DNA
  17. A DNA nucleotide contains 1 of 4 possible nitrogen bases
    • - Adenine, Guanine, Thymine, Cytosine
    • - Adenine and Guanine are Purines (double ring)
    • - Thymine and Cytosine are Pyrimidine (single ring)
    • - Each nucleotide contains a unique nitrogen base
    • - Nitrogen bases face inward: lie flat like stair steps
  18. What is dNTP?
    • -The triphosphate form of each nucleotide, used in the synthesis of a DNA polymer
    • - Any of the 4 nucleotides: dATP, dTTP, dCTP, dGTP
  19. Primary structure of DNA: monomers to polymer
    • - Dehydration synthesis, removes water
    •    -Removes -OH from 3'C of one nucleotide and -OH from phosphate group of other nucleotide
    • - Phosphodiester bond forms between 3'C and phosphate group
  20. The sugar/phosphate backbone is linear
    • 1.) Nucleotides are joined by covalent phosphodiester bonds. Covalent bonds are not easily broken
    • 2.) Polynucleotide chain is polar
    •    - at 5' end, free phosphate groups
    •    - at 3' end, free hydroxyl group
    • 3.) DNA chain can be tens of millions nucleotides long
    • 4.) Sugar/phosphate bonds form linear, unbranched, 'backbone' of DNA chain
  21. Double helix is stabilized by hydrogen bonds
    • - Hydrogen bonds form between slightly electronegative atoms (=O and =N in DNA) and slightly electropositive H's (-OH, -NH and -NH2)
    • - Hydrogen bonds are weak (3% strength of covalent bonds, easily broken by heat)
    • - 3 H-bonds between C and G
    • - 2 H-bonds between A and T
  22. Dimensions of a double-stranded DNA helix
    • - Always consistent, always 2.0nm
    • - Distanes between base pairs is 0.34nm
    • - 10 bases per turn of helix
    • - Each turn of helix is 3.4nm
    • - Helix is right-handed
  23. Hydrogen bondds in DNA
    • - Long double-stranded DNA helix is stabilized by an enormous number of H-bonds
    • - DNA is not permamently destroyed when H-bonds are broken
    • - DNA is destroyed when covalent bonds in sugar phosphate backbone is broken
  24. Implications of DNA secondary structure
    • - Complementarity: if know the sequence and polarity of one strand in the double helix, can predict the sequence and polarity of the complementarity strand
    • - If know the amount of 1 nitrogen base in the double helix, can predict the amount of the other 3
    •    - % purines in 1 strand = % pyrimidines in other
    •    - % purines in both = % pyrimidines in both of other

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