Chapter 11

• Chromosomes contain very long DNA molecules that are packed tightly.
• Supercoiling results from strain produced when rotations are added to a relaxed DNA molecule or removed from it.
• Overrotaion produced positive supercoiling
• Supercoiling is controlled by topoisomerase enzymes
• Compared to eukaryotic DNA

  bacterial (prokaryotic) DNA is not complex with histones and proteins.
• Each eukaryotic chromosome contains a single long linear DNA molecule that is bound to histone and by nonhistone chromosomal proteins.
• Euchromatin undergoes the normal cycle of decondensation and condensation in the cell cycle (less conceded)
• Heterochromatin remains highly condensed throughout the cell cycle

  (more condenced)
• Bacterial chromosomes exist in large loops and appears as nucleoid.
• Nucleosomes are folded in to 30-nm fiber that forms a series of 300-nm loops; they are anchored at their bases by proteins.
• The 300-nm loops are condensed to form a fiber that is itself tightly coiled to produce a chromatid
• Topologically associated domains (TADS) are chromatin areas that form spatial association regions within the interphase nucleus.
• Epigenetic changes are stable alterations of gene expression that don't require DNA sequence change.
• Chromosome regions undergoing active transcription are sensitive to digestion by DNAse 1, indicating that DNA Is more exposed during transcription.
• Centromeres are the regions of the chromosome where spindle microtubules attach; if cells don't have it, they usually are lost.
• Mitochondria and chloroplasts are eukaryotic organelles that posses their own DNA.
• Traits encoded by mtDNA and cpDNA are usually inhereted from a single parent, often the mother