Viral genomes are relatively small and can be composed of RNA or DNA
Viral genomes are packaged into the capsid in an assembly process
Bacterial Chromosomes
Bacterial chromosomes contain circular DNA molecules in which a few thousand gene sequences are interspersed with other functionally important sequences
The formation of chromosomal loops helps make the bacterial chromosome more compact
DNA supercoiling further compacts the bacterial chromosome
Chromosome function is influenced by DNA supercoiling
Eukaryotic Chromosomes
The sizes of eukaryotic genomes vary substantially
Eukaryotic chromosomes contain many functionally important sequences including genes, origins of replication, centromeres, and telomeres
The genome of eukaryotes contains sequences that are unique, moderately repetitive, and highly repetitive
Highly repetitive DNA can be separated from the rest of the chromosomal DNA by equilibrium density centrifugation
Sequence complexity can be evaluated in a renaturation experiment
Eukaryotic chromatin must be compacted to fit within the cell
Linear DNA wraps around histone proteins to form nucleosomes, the repeating structural unit of chromatin
The repeating nucleosome structure is revealed by digestion of the linker region
Nucleosomes become closely associated to form a 30 nm fiber
Chromosomes are further compacted by anchoring the 30 nm fiber into radial loop domains along the nuclear matrix
Condensin and cohesin promote the formation of metaphase chromosomes
