Eukaryotic Chromosome Organization

�4

Chromosome Organization• if all of the DNA was stretched out, it would measure

1.8 metres in length • How does it fit into a typical human cell nucleus, 10

micrometres in diameter? • there is a hierarchical organization • DNA is coiled around a group of 8 stabilizing

proteins called histones, forming nucleosomes

Chromosome Organization

Histones

Linkers

Nucleosome(8 histones)

Solenoid(6 nucleosomes)

Supercoil

�7

Prokaryotic DNA

Prokaryotic DNA• primary DNA is single circular chromosome • supercoiling happens in prokaryotes • plasmids are other circular pieces of DNA contained

in prokaryotes • plasmids can be exchanged through conjugation

�10

Telomeres

Telomeres• telomeres are non-coding, repetitive

sequences at the ends of chromosomes

Telomeres

Telomeres

Telomeres• during replication, the last 5’

end primer on the lagging strand is removed but not replaced with DNA

• This shortens the telomeres on each subsequent replication cycle

Telomeres• after many replications, telomeres will eventually

disappear, allowing coding DNA to be damaged • cell senescence- deteriorated functioning with

age as chromosomes shorten • Hayflick limit = total number of times a normal cell

can divide (about 50 in humans)

Dolly the Sheep

•