6.5 DNA Organization Flashcards
eukaryotic DNA organization
Negatively charged DNA is wrapped around
positively charged histone proteins
8 histone proteins combine to form…
a nucleosome which helps to wrap DNA
nucleosomes are further condensed to form…
solenoids (6 nucleosomes)
solenoids
aka chromatin fibres
-further coiled and folded until they form chromosomes
prokaryotic DNA organization
Commonly only one chromosome that can be
circular
No nuclear membrane
Smaller pieces of DNA float throughout the
cell and are called Plasmids
Plasmids can be shared between bacteria
super coiling
twisting of prokaryotic DNA to reduce the volume
telomere
a repeating sequence of DNA at the end of a chromosome. Protects coding regions
from being lost during replication.
DNA replication results in small amounts of
lost DNA after each replication
Telomeres help prevent the loss of important
parts of DNA
functions of telomeres
Help to prevent chromosome ends from
fusing to other chromosomes
Prevent DNA degradation from other enzymes
Assist DNA repair mechanisms in
distinguishing DNA breaks from chromosomal ends
Determine how many times a cell can divide
telomeres during replication
Telomeres shorten after each division
Cells can only divide so many times before
they lose their telomeres and important DNA
starts to become lost
hayflick limit
the total number of times a cell can divide
Human cells can divide around 50 times before
telomeres become too short
telomerase
adds more DNA to the
shortening telomeres of sex cells so they can continue to divide
Stem Cells and some White Blood Cells also use Telomerase
telomeres and aging
As we age more and more of our cells reach the Hayflick limit and begin to die off
Cancer cells can continue to divide indefinitely because they produce large amounts of Telomerase and continue to repair their telomeres
nucleosome
a unit of DNA storage, consisting of 8 histones with DNA strands wrapped around them
supercoiling
the continuous twisting of prokaryotic DNA that reduces the volume of the DNA
