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Eukaryotic Chromosome Organization
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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
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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
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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
•