Eucaryotic Chromosomes - PowerPoint PPT Presentation

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Eucaryotic Chromosomes

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  1. Eucaryotic Chromosomes • DNA is Enclosed in a Cell Nucleus • Packaged into a Set of Chromosomes • Chromosome sequence elements • Chromosome organization • Chromosome structure • Chromosome dynamics

  2. In Eucaryotes, DNA is Enclosed in a Cell Nucleus

  3. Packaged into a Set of Chromosomes

  4. Fluorescent in situ hybridization (FISH)

  5. FISH • Identify DNA sequences to be amplified • Attach fluorescent tags to complementary DNA to make a probe • PCR with tagged primers • Break purified DNA, denature, reanneal, extend with DNA polymerase and fluorescent substrates • Denature target DNA “in situ” • In place, cell or tissue preparation on microscope slide • Hybridize • Soak immobile target DNA in solution of tagged probes under denaturing conditions • Slowly cool to allow double strands to form • Wash off unhybridized probe

  6. Chromosome sequence elements • Centromeres (1) • Ensure proper chromosome segregation • Telomeres (2) • Mark and protect the ends of chromosomes • Replication origins (tens to hundreds) • Provide sites for the initiation of DNA synthesis • Genes (thousands) • Repeated sequences (many thousands)

  7. Origins, Centromeres, Telomeres and Chromosome function

  8. Chromosome 22

  9. Repeated elements

  10. Chromosome evolution:Global organization is highly variable

  11. Chromosome evolutionMice and Humans

  12. Comparisons Between the DNAs of Related Organisms Distinguish Conserved and Nonconserved Regions of DNA Sequence

  13. Chromosomes Exist in Different States Throughout the Life of a Cell

  14. Nucleosomes Are the Basic Unit of Eucaryotic Chromosome Structure

  15. The Structure of the Nucleosome Core Particle Reveals How DNA Is Packaged

  16. Histone Core Schematics

  17. The Positioning of Nucleosomes on DNA Is Determined by Both DNA Flexibility and Other DNA-bound Proteins

  18. The 60 nm Chromatin Fiber is dependent on the linker histone H1

  19. ATP-driven Chromatin Remodeling Machines Change Nucleosome Structure

  20. Covalent Modification of the Histone Tails Can Profoundly Affect Chromatin

  21. Modification are specific for different functions

  22. THE GLOBAL STRUCTURE OF CHROMOSOMES • Chromatin is arranged in domains • Large loops of DNA attached to common scaffold • Heterochromatin is compact and inaccessible for transcription • Chromatin structure is important for the mitosis, recombination and global control of gene expression

  23. Lampbrush Chromosomes Contain Loops of Decondensed Chromatin

  24. Drosophila Polytene Chromosomes Are Arranged in Alternating Bands and Interbands

  25. Heterochromatin Is Highly Organized and Usually Resistant to Gene Expression

  26. Variegated phenotypes arise from clonal inheritance of chromatin structure

  27. The Ends of Chromosomes Have a Special Form of Heterochromatin

  28. Centromeres Are Also Packaged into Heterochromatin

  29. Sequence and structure of a human centromere

  30. Heterochromatin May Provide a Defense Mechanism Against Mobile DNA Elements • Repeated DNA sequences often are clusters of mobile elements • Different elements can replicate through either RNA or DNA intermediates • Packaging repeats in heterochromatin may keep them from spreading • RNA interference can play a role in silencing and heterchromatin mainenance

  31. Mitotic Chromosomes Are Formed from Chromatin in Its Most Condensed State

  32. Individual Chromosomes Occupy Discrete Territories in an Interphase Nucleus

  33. Molecular genetic processes may take place in localized “factories”