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Genes and Genomes

Genes and Genomes. Prokaryotic Cells. No nucleus and no organelles. Eukaryotic Cells. Cell Structure Differences. DNA: The Molecule of Life. Evidence that DNA is the Inherited Genetic Material 1869 Friedrich Miescher: “nuclein” Could not be broken down by proteases

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Genes and Genomes

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  1. Genes and Genomes

  2. Prokaryotic Cells • No nucleus and no organelles

  3. Eukaryotic Cells

  4. Cell Structure Differences

  5. DNA: The Molecule of Life • Evidence that DNA is the Inherited Genetic Material • 1869 Friedrich Miescher: “nuclein” • Could not be broken down by proteases • Had acidic properties: “nucleic acids” • 1928 Frederick Griffith • Two strains of Streptococcus pneumoniae • Virulent smooth strain (S cells) and harmless rough strain (R cells) • Demonstrated transformation

  6. Evidence that DNA Is the Inherited Genetic Material • 1944 Oswald Avery, Colin MacLeod, and Maclyn McCarty • Purified DNA from large batches of Streptococcus pneumoniae • Exposed to protease, RNAses, or DNAses • Experiment proved that DNA was the transforming factor in the Griffith experiments

  7. Nucleotide Structure

  8. DNA Structure • James Watson and Francis Crick revealed the definitive structure of DNA • “The Molecular Structure of Nucleic Acids: A Structure for Deoxyribose Nucleic Acid” published in Nature on April 25, 1953

  9. Complementary Antiparallel Strands

  10. Difference Between Prokaryotic and Eukaryotic Chromosomes

  11. Prokaryotic Genome Structure • Prokaryotes have single circular chromosome. DNA replication can occur bidirectionally (fast!) • One DNA can generate multiple mRNA transcripts, which can have multiple Ribosomes translating to protein

  12. Eukaryotic Genome Structure • Two features of eukaryotic genomes are a major information-processing challenge: • First, the typical eukaryotic genome is much larger than that of a prokaryotic cell • Second, cell specialization limits the expression of many genes to specific cells • The DNA-protein complex, called chromatin, is ordered into higher structural levels than the DNA-protein complex in prokaryotes

  13. Chromatin structure is based on successive levels of DNA packing • Eukaryotic chromosomes contain an enormous amount of DNA relative to their condensed length • If you were to stretch out a human cell’s DNA, it would be about 2-3 meters in length

  14. Nucleosomes, or “Beads on a String” • In electron micrographs, unfolded chromatin has the appearance of beads on a string • Each “bead” is a nucleosome, the basic unit of DNA packing

  15. LE 19-2a 2 nm DNA double helix His- tones Histone tails 10 nm Histone H1 Nucleosome (“bead”) Linker DNA (“string”) Nucleosomes (10-nm fiber)

  16. In a mitotic chromosome, the looped domains coil and fold, forming the metaphase chromosome 700 nm 1,400 nm Metaphase chromosome

  17. Haploid and Diploid (Humans N= 23) • Haploid • N • 23 chromosomes • Sex cell • Diploid • 2N • 46 Chromosomes • Somatic cells Mutations can cause: Triploid (3N), 4N, 5N…

  18. Human Karyotype Sex chromosomes Autosomes Total number of chromosomes in a human: 46 (23 from each parent, 44 autosomes and 2 sex chromosomes)

  19. How many genetic problems can you find?

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