Chapter 12
Molecular Structure and Organization of Chromosomes
Study Outline
1. Organization of sites along bacterial chromosomes
2. Structure of bacterial chromosomes
a. The formation of chromosomal loops helps make the bacterial chromosome more
compact
b. DNA supercoiling further compacts the bacterial chromosome
c. Chromosome function is influenced by DNA supercoiling
3. Organization of sites along the eukaryotic chromosome
4. Sizes of eukaryotic genomes and repetitive sequences
a. The sizes of eukaryotic genomes vary substantially
b. The genomes of eukaryotes contain sequences that are unique, moderately repetitive, or
highly repetitive
5. Structure of eukaryotic chromosomes in nondividing cells
a. Linear DNA wraps around histone proteins to form nucleosomes, the repeating structural
unit of chromatin
b. The repeating nucleosome structure is revealed by digestion of the linker region
c. Nucleosomes become closely associated to form a 30nm fiber
d. Chromosomes are further compacted by anchoring the 30nm fiber into radial loop
domains along the nuclear matrix
6. Structure of eukaryotic chromosomes during cell division
a. Metaphase chromosomes are highly compacted.
b. Condensin and cohesin promote the formation of metaphase chromosomes