1. Viral genomes contain DNA or RNA and are packaged into capsids through assembly processes. Bacterial chromosomes contain genes and other sequences compacted by looping and supercoiling. 2. Eukaryotic chromosomes vary greatly in size and contain genes and other sequences. Their DNA must be highly compacted to fit in the nucleus. 3. Eukaryotic DNA wraps around histone proteins to form nucleosomes, which further compact to form chromatin fibers and loop domains anchored to the nuclear matrix. Additional compaction occurs during cell division through condensin and cohesin proteins.

1. Genetics: Analysis and Principles By Robert J. Brooker CHAPTER 10 CHROMOSOME ORGANIZATION AND MOLECULAR STRUCTURE

4. Animal virusses Lipid bilayer Picked up when virus leaves host cell

12. Terms and concepts to know: Compaction Coiling Supercoiling Gyrase topoisomerase

13. Plates preventing DNA ends from rotating freely Fewer turns More turns Both overwinding and underwinding can induce supercoiling Figure 10.7 These three DNA conformations are topoisomers of each other These two DNA conformations do not occur in living cells

14. Increasing of ‘coiling’ of the double helix in eukaryotes also occur: - DNA replication - transcription, RNA synthesis from a double stranded DNA

15. Figure 10.8 It makes transcription and translation easier, because the chains melt easier. negative supercoiling Does not only lead to a more compacted nucleoid

18. Has a genome that is more than twice as large as that of Genome size is very various, especially because of the presence of Repetitive DNA

20. Prevent chromosome sticky ends and shortening Required for proper segregation during mitosis and meiosis Eukaryotic chromosomes contain many origins of replication approximately 100,000 bp apart Figure 10.11

25. Eukaryotic Chromatin Compaction `````` Samenstelling relatieve hoeveelheid Histon eiwitten 115 Non-histon eiwitten 33 RNA 1 100 DNA

28. Play a role in the organization and compaction of the chromosome Figure 10.13

29. Regular, spiral configuration containing six nucleosomes per turn Irregular configuration where nucleosomes have little face-to-face contact Figure 10.16

33. Figure 10.14

34. The Data Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 30 units ml-1

35. Interpreting the Data Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display All chromosomal DNA digested into fragments that are ~ 200 bp in length These longer pieces were all in multiples of 200 bp At low concentrations, DNase I did not cut at all the linker DNA This fragment contains two nucleosomes And this, three 30 units ml-1

36. Figure 10.15a ‘ BEADS ON A STRING’

37. Figure 10.15b ‘ BEADS ON A STRING’ + linker histone H1

40. The levels of compaction leading to a metaphase chromosome

41. The levels of compaction leading to a metaphase chromosome Figure 10.21

42. Compaction level in euchromatin Compaction level in heterochromatin During interphase most chromosomal regions are euchromatic Figure 10.21

46. Figure 10.20 The histon-code 1. Lysines may be acetylated 2. Serines may be phoshorylated 3. arginines may be methylated

48. Eukaryotic Chromosome

50. Metaphase Chromosomes Figure 10.22 (The scaffold)

52. Cohesins along chromosome arms are released The alignment of sister chromatids via cohesin

53. The number of loops has not changed However, the diameter of each loop is smaller Condesin travels into the nucleus Condesin binds to chromosomes and compacts the radial loops During interphase, condensin is in the cytoplasm The condensation of a metaphase chromosome by condensin Model !

54. ‘ Chromosome territories’ chromosomen nemen een bepaalde ruimte in in de nucleus: Geen spaghetti Chromosome of a chicken Nucleus where each chromosome is colored differently