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Heinrich Wilhelm Gottfried Waldeyer 1888 What is so special about chromosomes ? 1.They are huge: One bp = 600 dalton, an average chromosome is 107 bp long = 109- 1010 dalton ! (for comparison a protein of 3x105 is considered very big. What is so special about chromosomes ? 1.They are huge: One bp = 600 dalton, an average chromosome is 107 bp long = 109- 1010 dalton ! (for comparison a protein of 3x105 is considered very big. 2. They contain a huge amount of non- redundant information (it is not just a big repetitive polymer but it has a unique sequence) . What is so special about chromosomes ? 1.They are huge: One bp = 600 dalton, an average chromosome is 107 bp long = 109- 1010 dalton ! (for comparison a protein of 3x105 is considered very big. 2. They contain a huge amount of non- redundant information (it is not just a big repetitive polymer but it has a unique sequence) . 3. There is only one such molecule in each cell. (unlike any other molecule when lost it cannot be re- synthesized from scratch or imported) • Philosophically - the cell is there to serve, protect and propagate the chromosomes. • Practically - the chromosome must be protected at the ends - telomers and it must have “something” that will enable it to be moved to daughter cells - centromers Genome Complexity Lesson 2 - Chromosome structure • The DNA compaction problem • The nucleosome histones (H2A, H2B, H3, H4) • The histone octamere • Histone H1 the linker histone • Higher order compactions • Chromatin loops and scaffolds (SAR) • Non histone chromatin proteins • Heterochromatin and euchromatin • Chromosome G and R bands • Centromeres Lesson 2 - Chromosome structure • The DNA compaction problem • The nucleosome histones (H2A, H2B, H3, H4) • The histone octamere • Histone H1 the linker histone • Higher order compactions • Chromatin loops and scaffolds (SAR) • Non histone chromatin proteins • Heterochromatin and euchromatin • Chromosome G and R bands • Centromeres • Take 4 meters of DNA (string) and compact them into a ball of 10µM. Now 10µM are 1/100 of a mm and a bit small to imagine – so now walk from here to the main entrance let say 400 meters and try to compact it all into 1 mm. • This compaction is very complex and the DNA isn’t just crammed into the nucleus but is organized in a very orderly fashion from the smallest unit - the nucleosome, via loops, chromosomal domains and bands to the entire chromosome which has a fixed space in the nucleus.