AP Bio Ch 16 part 1

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  • 1. CH 16: The Molecular Basis of Inheritance Francis Crick James Watson
  • 2. Major Concepts • The discovery of DNA as the genetic material • How DNA is replicated and repaired To assist in your note taking, key concepts have been underlined and vocab terms are in orange
  • 3. Life’s Operating Instructions DNA is an example of a nucleic acid Of all the macromolecules, nucleic acids are the only ones that can replicate themselves DNA is the chemical language that is responsible for biochemical, anatomical, physiological, & even some behavioral traits
  • 4. DNA is the Genetic Material… But How Do We Know??? The Debate: DNA vs. Protein In the 1940’s…. Proteins Nucleic Acids: DNA •A very wide variety was known •Little was known about them •They were known to •They seemed too be very specific simple to account for the great diversity of life
  • 5. Building a Case for DNA: DNA Can Transform Bacteria Frederick Griffith’s Experiment, 1928 Transformation: The uptake & assimilation of external DNA by a bacterial cell that virulent results in a change in genotype and phenotype Concl: Living R bacteria were transformed into S bacteria by a heritable substance from the dead S cells harmless
  • 6. Quick Think Describe Griffith’s experiment & the conclusion that he reached What was the change in phenotype that the transformed Streptococcus pnumoniae underwent?
  • 7. Follow-up to Griffith’s Experiment Griffith new that something from the heat-killed S bacteria was transforming the harmless R strain, but he didn’t know what… Oswald Avery was determined to pick up where Griffith left off…. How would YOU design an experiment to figure out which part of the pathogenic bacteria was transforming the harmless bacteria???
  • 8. Avery performed Griffith’s experiments, but treated the nonpathogenic bacteria with isolated molecules from the heat-killed pathogenic strain Lysed cells DNA was the only macromolecule to successfully transform the R strain
  • 9. When Avery concluded that DNA was the transforming agent, few took interest! Most were hung up on the idea that protein was the genetic material…..plus not much was known about DNA at that point……
  • 10. Building a Case for DNA: Viral DNA Can Program Cells Background Info •The T2 virus infects the bacteria E. coli •The T2 virus is made mostly of DNA & protein Viral DNA injected into cell •A virus must infect a cell in order to reproduce •A Bacteriophage ( AKA phage) is a virus that infects bacterial cells
  • 11. Building a Case for DNA: Viral DNA Can Program Cells In 1952, the research duo Alfred Hershey & Martha Chase wanted to figure out whether it was viral protein or its DNA that caused a cell to become a virus factory
  • 12. Building a Case for DNA: Chargaff’s Investigations, 1947 •Chargaff found diversity in the DNA molecules of different organisms: Various organisms had different percentages of the 4 bases nucleotide Each nucleotide of DNA has 3 parts- •Chargaff’s Rule: In any given organism, the % of A in DNA = the % of T. In the same way, % G = % C
  • 13. Quick Think Human DNA is composed of 30% thymine. What would be the percent composition for the other three bases??
  • 14. Building a Case for DNA: Additional Evidence Prior to cell division, eukaryotic cells make exact copies of their DNA and then the DNA is distributed evenly among the daughter cells.
  • 15. DNA as the Genetic Material: How Does Form Fit Function? By the early 1950’s, the race was on to find the 3-D structure of DNA In 1950 Maurice Wilkins & Rosalind Franklin were hard at work using X-ray diffraction technique to figure out DNA structure They planned to use mathematical equations derived from the diffraction images to determine the 3-D structure of DNA.
  • 16. DNA as the Genetic Material: How Does Form Fit Function? Watson & Crick used Franklin’s x-ray diffraction images to deduce the following: •DNA is a double helix withwith T and C Base-pairing rules: A pairs a sugar-phosphate backbone on the •Watson & Crick’s model suggested the basic mechanismon the pairs with G. “ladder” and relatively hydrophobic bases for outside of theIn other words, purines always DNA with bases are the rungs of the ladder. bond replication inside; the pyrimidines.
  • 17. Quick Think How did Watson & Crick’s model explain the basis for Chargaff’s rule?