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Announcements

Announcements. Exam 2 next week: 10/17, 18, and 20 . Same format as exam 1, a bit shorter. You will need a bluebook again. Answers from exam 1 will be removed from lab when exam 2 answers go up. Homework/ problem set 4 (15 pts) due next week in lab.

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Announcements

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  1. Announcements Exam 2 next week: 10/17, 18, and 20. Same format as exam 1, a bit shorter. You will need a bluebook again. Answers from exam 1 will be removed from lab when exam 2 answers go up. Homework/ problem set 4 (15 pts) due next week in lab. Handout for transformation lab available Monday.

  2. Homework (15 pts) - BIO 326 Genetics • Due 10/15,16 in lab • 1. Are sex chromosome aneuploids or autosomal aneuploids more common in humans? Give one reason to explain your answer. • 2. Red-green color blindness is an X-linked recessive disorder. A young man with a 47, XXY karyotype (Klinefelter syndrome) is color blind. His 46, XY brother is also color blind. Both parents have normal color vision. Where did the nondisjunction occur that gave rise to the young man with Klinefelter syndrome? • 3. Would a human with 2 X chromosomes and 2 Y chromosomes be male or female? • 4. Predict the sex of Drosophila with the following chromosome compositions (A = haploid set of autosomes): • a. 4X 4A • b. 3X 4A • c. 1X 2A • 5. Mark true or false for the following relations regarding the percentages of bases in a double-stranded DNA molecule: • a. A + T = G + C • b. A + G = T + C • c. A + C = G + T • d. A + T = 1.0 • C + G • e. A = T • G C

  3. Review of Last Lecture Polyploidy Variation in structure/arrangement of chromosomes - deletion - duplication - inversion -translocation What are criteria for genetic material?

  4. Outline of Lecture 19 I. Evidence that DNA is genetic material II. DNA and RNA: Composition and Function III. History of solving the structure of DNA

  5. I. DNA Structure and analysis What is the genetic material? Chromosomes contain protein and DNA - which is it? What must genetic material do? 1. Replication 2. Storage of information 3. Expression of information 4. Variation by mutation - evolution

  6. The Flow of Genetic Information (The Central Dogma) Trait

  7. Is the Genetic Material Protein or DNA? • Many favored proteins until the mid-1940’s. • DNA is simple chemically (4 nucleotides known); how could it then hold complex genetic information? • Proteins are much more complicated chemically (20 amino acids) and more abundant; perhaps they hold genetic information.

  8. Evidence for DNA as Hereditary Molecule • Transformation studies • Griffith (1927) • Avery, MacLeod and McCarty (1944) • Hershey-Chase experiment (1952) • Chargaff’s Rules • Molecular Studies

  9. Griffith’s Transformation Expt. Bacteria Used Living smooth (virulent) Living rough (avirulent) Killed smooth Living rough + killed smooth Conclusion: Killed smooth converted living rough to virulent cells A Transforming Principle (some smooth component) is responsible. Expected mouse to live

  10. Avery, MacLeod, and McCarty Expt:DNA is the “Transforming Principle” IIIS IIIS filtrate IIR + IIIS filtrate Active factor Is DNA!

  11. Hershey-Chase Experiment • Study of infection of E. coli by T2 phage • Radioactively labeled DNA and protein: • 32P atom is in phosphate molecules in DNA and RNA, only at low levels in protein (phosphorylated proteins). • 35S atom is in sulfur-containing amino acids (cysteine and methionine); not in DNA or RNA.

  12. Phage Made Radioactive Non-radioactive medium + bacteria

  13. Phage Infect Cells 32P Phage 35S Phage Label (protein) is outside Label (DNA) is inside

  14. Is DNA the genetic material in eukaryotes? Indirect evidence -DNA and RNA absorb UV Light • Action spectrum of UV-induced mutations in bacteria correlates with absorption spectrum of UV light for nucleic acids, not protein. • Can use to quantify amounts of nucleic acid and protein. Direct evidence?

  15. RNA is the Hereditary Material in RNA Viruses, e.g. TMV Tobacco Mosaic Virus

  16. Reconstitution of Hybrid TMV (Fraenkel-Conrat & Singer) Strain 1 Strain 2 Lesions corresponded to RNA

  17. II. Structure of DNA/RNABases and Sugars pyrimidines T C U purines G A Ribose sugars

  18. Bases and Sugars in DNA and RNA • In DNA: deoxyribose + A, T, G or C • dA deoxyadenosine • dT deoxythymidine • dG deoxyguanosine • dC deoxycytidine • In RNA: ribose + A, U, G, or C • A adenosine • U uridine • G guanosine • C cytidine

  19. Nucleoside = Base + SugarNucleotide = Nucleoside + Phosphate U dAMP

  20. dNDP’s and dNTP’s:Note Errors in the Text deoxy deoxy deoxy deoxy dNTP (dATP) dNDP (dTDP)

  21. 3’ to 5’ Phosphodiester Bonds Make the Sugar-Phosphate Backbone New monomers add here Strand has 5’-PO4 end and 3’-OH end

  22. Chargaff’s Rules - also evidence for DNA as genetic material • 1949-1953, quantified amounts of each base in DNA from different species. • In every species, amount of A = amount of T, and amount of G = amount of C • If that’s true, then A + G = C + T • The % GC and % AT varied from species to species, but always adds up to 100%.

  23. III. History of structure of DNA:Rosalind Franklin and Maurice Wilkins found X-ray Diffraction Evidence for DNA Double Helix

  24. Linus Pauling and Robert Corey at Cal Tech were in the Race to Determine DNA structure

  25. James Watson and Francis Crick Used Molecular Modeling to Deduce DNA structure

  26. The DNA Double Helix DNA structure • Double helical • major, minor grooves • right-handed • bases are 3.4 Å apart (10 Å = 1 nm) • 10 bases/turn • Complementary Base Pairing • through H bonds: A=T, GC • Antiparallel Strands • 5’ to 3’ • 3’ to 5’

  27. Right- and Left-handed DNA

  28. Base-Pairing in DNA A=T GC

  29. Reading DNA Strands Single strand of DNA: 5’-AGCATTCG-3’ 3’-TCGTAAGC-5’ Complementary strand of above, usually written 5’ to 3’: 5’-CGAATGCT-3’ Double-stranded fragment is written: 5’-AGCATTCG-3’ 3’-TCGTAAGC-5’

  30. Denaturation/Renaturation Which DNA has higher GC content and why?

  31. Nucleic Acid Hybridization Molecular probes can “fish out” a specific DNA from a mixture

  32. Nucleic Acid Gel Electrophoresis

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