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DNA the carrier of genetic information
1) Archibald Garrod hypothesized in 1909 that genes control enzymes, which catalyze chemical processes in cells and cause inherited diseases when certain enzymes cannot be produced. 2) Beadle and Tatum's "One Gene, One Enzyme Hypothesis" in the 1940s proposed that each gene directs the production of a single enzyme. 3) Experiments in the 1950s-1960s provided evidence that DNA, not proteins, carries the genetic information through transformation, viral infection, and replication experiments.
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Discusses Garrod’s hypothesis linking genes and enzymes to traits and genetic diseases.
Describes alkaptonuria, a metabolic disorder affecting urine color.
Covers the contributions of Beadle and Tatum regarding gene function and evidence supporting DNA as hereditary material.
Describes Griffith's and Avery's experiments that established DNA as the genetic material in bacteria.
Outlines the structure of DNA, including nucleotide composition and Rosalind Franklin's X-ray diffraction studies.
Details Chargaff's findings on base compositions and the rules for base pairing in DNA.
Describes the semiconservative nature of DNA replication, the roles of enzymes, and telomere functions.
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DNA the carrier of genetic information
- 2. How does theDNA lead to specific traits??? Archibald Garrod (1909) hypothesized: “proteins are the link between genotype & phenotype”
- 3. 1909 - ArchibaldGarrod Suggested genes control enzymes, & enzymes catalyze chemical processes in cells. Inherited Diseases are “inborn errors of metabolism” where a person can’t make an enzyme.”
- 4. Example Alkaptonuria where urineturns black after exposure to air
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- 6. • G. Beadle &Edward Tatum Nobel Prize in Physiology or Medicine 1958 "for their discovery that genes act by regulating definite chemical events"
- 10. One Gene, OneEnzyme Hypothesis -Beadle & Tatum each gene dictates the production of one enzyme each mutant lacks the ability to produce an enzyme
- 11. *Some proteins arenot enzymes (ex. insulin) *Some proteins are made of more than one polypeptide chain (hemoglobin) *Each chain specified by its own gene One Gene, One Polypeptide Hypothesis -Beadle & Tatum (revisited)
- 12. Evidence of DNAas hereditary material › Proteins rather than nucleic acids thought to be genetic material in the 1930s and 1940s › Several lines of evidence supported DNA as genetic material DNA is transforming principle in bacteria › Watson and Crick modeled DNA structure
- 13. Griffith’s transformation experiments OswaldAvery Frederick Griffith Colin MacLeod
- 14. Established that DNAcarries necessary information for bacterial transformation
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- 16. Hershey-Chase experiments Established that viral DNAenters bacterial cells and is required for synthesis of new viral particles Alfred Hershey Martha Chase
- 17. Structure ofDNA › Regular polymer of nucleotides Nitrogenous base of purine or pyrimidine Base covalently links to deoxyribose Deoxyribose covalently bonds to a phosphate group › Backbone Alternating sugar and phosphate groups joined by covalent phosphodiester linkages
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- 20. x-ray diffraction studies Carried outby Rosalind Franklin on crystals of purified DNA Born: July 25, 1920 Died: April 16, 1958
- 21. X-ray diffraction imageof DNA
- 22. three major typesof regular, repeating patterns in the molecule with the dimensions 0.34 nanometer, 3.4 nanometers, and 2.0 nanometers were evident.
- 23. Watson and Crickbegan to pursue the problem of DNA structure each pair of bases is exactly 0.34 nanometer from the adjacent pairs above and below Because exactly ten base pairs are present in each full turn of the helix, each turn is 3.4 nanometers high DNA molecule is 2.0 nm wide.
- 24. Structure of DNAmolecule › Two polynucleotide chains associated as double helix › Two chains are antiparallel (running in opposite directions) › The sugar-phosphate backbones of the two chains form the outside of the helix › The bases belonging to the two chains associate as pairs in the center
- 25. 3-D model of DNAdouble helix James D. Watson Francis Crick
- 26. Erwin Chargaff the basecomposition of DNA from a number of organisms and tissues had been determined Regardless of the source of the DNA “ratios of purines to pyrimidines and also of adenine to thymine and ofguanine to cytosine were not far from 1.
- 27. Base compositions in DNAfrom selected organisms
- 28. Base-pairing rules forDNA › Hydrogen bonding between base pairs holds together the two chains of helix › Adenine (A) forms two hydrogen bonds with thymine (T) › Guanine (G) forms three hydrogen bonds with cytosine (C) › Chargaff’s rules A=T G=C
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- 31. DNA REPLICATION isSEMICONSERVATIVE One way to accomplish this is to use a heavy-nitrogen isotope,nitrogen-15 (ordinary nitrogen is nitrogen-14) Matthew Meselson and Franklin Stahl grew cells of the bacterium Escherichia coli on a medium that contained nitrogen-15 in the form of ammonium chloride (NH4Cl) Matthew Meselson Franklin Stahl
- 33. DNA Replication › Twostrands of double helix unwind › Each strand serves as template for new strand › DNA polymerase adds new nucleotide subunits › Additional enzymes and other proteins required to unwind and stabilize DNA helix
- 34. › Bidirectional, startingat origin of replication › Strands replicate at replication fork › Two DNA polymerase molecules catalyze replication Leading strand Lagging strand
- 35. Enzymes involved in DNAreplication
- 36. Simplified view ofDNA replication
- 37. Overview of DNAreplication
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- 39. Bidirectional DNA replicationin bacteria and eukaryotes
- 40. Replication › Telomeres atchromosome ends Short, non-coding repetitive DNA sequences Shorten slightly with each cell cycles Can be extended by telomerase Absence of telomerase activity may be cause of cell aging › Most cancer cells have telomerase to maintain telomere length and resist apoptosis
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