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Ch 5 and16 A Close Look at the Hereditary Molecules

Ch 5 and16 A Close Look at the Hereditary Molecules. Protein sequence-->programmed by genes Genes are made of DNA, a nucleic acid. DNA. Synthesis of mRNA in the nucleus. mRNA. NUCLEUS. CYTOPLASM. mRNA. Movement of mRNA into cytoplasm via nuclear pore. Ribosome.

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Ch 5 and16 A Close Look at the Hereditary Molecules

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  1. Ch 5 and16 A Close Look at the Hereditary Molecules • Protein sequence-->programmed by genes • Genes are made of DNA, a nucleic acid

  2. DNA Synthesis of mRNA in the nucleus mRNA NUCLEUS CYTOPLASM mRNA Movement of mRNA into cytoplasm via nuclear pore Ribosome Synthesis of protein Amino acids Polypeptide Flow of genetic information LE 5-25 DNA RNA Protein

  3. The Roles of Nucleic Acids • Two types: • Deoxyribonucleic acid (DNA) • Ribonucleic acid (RNA) • DNA provides directions for its own replication. • DNA directs synthesis of messenger RNA (mRNA) • mRNA controls protein synthesis. • Protein synthesis occurs on ribosomes.

  4. 5¢ end Nucleic acid building block LE 5-26a Nucleoside Nitrogenous base Phosphate group Pentose sugar Nucleotide 3¢ end Polynucleotide, or nucleic acid

  5. Nucleic Acid Structure Monomers nucleotide (3 parts) 1. nitrogenous base 2. 5 C sugar 3. Phosphate nucleoside Polymer polynucleotide or nucleic acid

  6. Nitrogenous bases Pyrimidines LE 5-26b Uracil (in RNA) U Cytosine C Thymine (in DNA) T Purines Guanine G Adenine A Pentose sugars Deoxyribose (in DNA) Ribose (in RNA) Nucleoside components

  7. Important Nucleic Acid Distinctions Two kinds of bases • Pyrimidines-one ring (T,U,C) • Purines- two rings (G,A) DNA the sugar = deoxyribose NO 2’ OH (hydroxyl) RNA the sugar= ribose YES 2’ OH

  8. Nucleotide Polymers • Nucleotides (nt) connect through phosphodiester bond 5’ Phosphate-->3’OH • Creation of a sugar-phosphate backbone with bases as appendages. • Sequence of bases along DNA or mRNA polymer unique for each gene.

  9. LE 16-7 5 end Hydrogen bond 3 end 1 nm 3.4 nm 3 end 0.34 nm 5 end Key features of DNA structure Partial chemical structure Space-filling model Two DNA strands bind together through complementary base-pairing.

  10. Structure of DNA double helix: published in 1953 FrancisCrick JamesWatson Watson JD, Crick FHC. 1953. Molecular structure of nucleic acids: a structure for deoxyribonucleic acids. Nature 171:738.

  11. Partly based on Franklin’s x-ray diffraction data LE 16-6 Franklin’s X-ray diffraction photograph of DNA Rosalind Franklin

  12. LE 16-8 Chargaff’s rules (1940s): Amount of A=T G=C

  13. Purine + purine: too wide Pyrimidine + pyrimidine: too narrow Purine + pyrimidine: width consistent with X-ray data Watson & Crick: built model of DNA and tested possible combinations of bases LE 16-UN298 Did model support Chargaff’s observations and Franklin’s x-ray diffraction data?

  14. Antiparallel DNA strands LE 16-7 5 end Hydrogen bond 3 end 1 nm 3.4 nm 3 end 0.34 nm 5 end Key features of DNA structure Partial chemical structure Space-filling model Two DNA strands bind together through complementary base-pairing.

  15. The DNA Double Helix • Two polynucleotides (strands) base-paired together GC, AT (complementary base-pairing) • Double helix • Two sugar-phosphate backbones run in opposite 5´ to 3´ directions - antiparallel • One DNA molecule includes many genes

  16. Sugar Sugar Adenine (A) Thymine (T) Sugar Sugar Guanine (G) Cytosine (C) Complementary base pairs A=T 2 H-bonds G=C 3 H-bonds

  17. Behavior of DNA Draw a 10 base pair double-stranded DNA (dsDNA) that is rich in AT. Draw a 10 base pair double-stranded DNA (dsDNA) that is rich in GC. If these were placed in a tube of boiling water what would happen? DNA would become single stranded (ssDNA) (denatured or melted). Which DNA would denature first. Why? AT rich fragment less stable 2 H-bonds/bp versus 3 H-bonds/bp

  18. DNA Used as Evolutionary Ruler • Linear sequences of DNA in chromosomes • passed from parents to offspring • Two closely related species are more similar in DNA sequence than distantly related species • Similarity of DNA sequence • Determines evolutionary relatedness

  19. Compare the human sequence to the frog and mouse. Which sequence is most similar to human? human 5’ GAACCTTCCAATTGATCT3’ 5’ GAACCAACCAATTAAACT3’ 5’ GAACCTTCGAATTGATCT3’ frog mouse 2. Write in the complementary strand for each.

  20. Earlier data suggested that DNA was hereditary material Model system: Drosophila melanogaster Investigator: Thomas Hunt Morgan (early 1900’s) Evidence: white eye phenotype associated with X-chromosome Model system: bacteria and viruses Investigators: Many Evidence: various

  21. Evidence That DNA Can Transform Bacteria Evidence for genetic role of DNA (Frederick Griffith,1928) Heat-killed pathogenic “S” Streptococcus pneumoniae + “R”non-pathogenic bacterial strain Some living bacteria became pathogenic Transformation of “R’ to ‘S”, How could one determine pathogenicity experimentally?

  22. Mixture of heat-killed S cells and living R cells Heat-killed S cells (control) Living R cells (control) Living S cells (control) LE 16-2 RESULTS Mouse dies Mouse healthy Mouse healthy Mouse dies Living S cells are found in blood sample

  23. What molecule was responsible for conferring a new phenotype into an organism? • Oswald Avery, Maclyn McCarty, and Colin MacLeod (1944) • Published results • Showed DNA from bacteria NOT protein--> caused transformation of “R” to “S”

  24. Independent confirmation • Alfred Hershey and Martha Chase (1952) • Used bacterial virus (bacteriophage) (T2) to ask whether DNA or protein was hereditary material

  25. Phage head LE 16-3 Tail Tail fiber DNA 100 nm Bacterial cell

  26. Hershey & Chase labeling experiment Empty protein shell LE 16-4 Radioactive protein Radioactivity (phage protein) in liquid Phage Bacterial cell Batch 1: Sulfur (35S) DNA Phage DNA Protein radiolabelled Centrifuge Pellet (bacterial cells and contents) Radioactive DNA Batch 2: Phosphorus (32P) DNA radiolabelled Centrifuge Radioactivity (phage DNA) in pellet Pellet Phage produced in and released from bacteria with radioactive DNA.

  27. Hershey & Chase results -Suggest that DNA, not protein, is transferred to bacteria by phage. -DNA programs the reproduction of more phage. Contains important genetic instructions.

  28. I’m a pretty cool molecule but I’ll still answer your questions.

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