Eukaryotic replicons are 40 to 100 kb in length and individual replicons are activated at characteristic times during S phase.

TLS Online TPP Program

#Id: 421

#Unit 2. Cellular Organization

The nucleosome is 200 bp of DNA, organized by an octamer of small, basic histone proteins into a beadlike structure. 

TLS Online TPP Program

#Id: 422

#Unit 2. Cellular Organization

The nucleosome is of 10nm/100A diameter, compacting the DNA about 6-fold over the length of naked DNA. Its first level of organization. 200X3.4A=680A

TLS Online TPP Program

#Id: 423

#Unit 2. Cellular Organization

The second level of organization is the coiling of the 10-nm fiber of nucleosomes into a helical array to constitute the fiber of diameter 30 nm.

TLS Online TPP Program

#Id: 424

#Unit 2. Cellular Organization

30 nm compacts the DNA 40-fold. This structure of this fiber requires the histone tails and is stabilized by linker histones.

TLS Online TPP Program

#Id: 425

#Unit 2. Cellular Organization

This 30-nm fiber is further folded, results in 1000-fold compaction in euchromatin in interphase chromatin and in mitotic chromosomes to achieve an overall 10,000- fold compaction in euchromatin.

TLS Online TPP Program

#Id: 426

#Unit 2. Cellular Organization

Heterochromatin generally maintains 10,000-fold compaction in both interphase and mitosis after 30 nm.