DNA replication
Lecture Notes
Written by: Mais Kalbouneh
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Most of the DNA is introns
Introns are 10 times the number of exons
Introns are involved in regulation or splicing
The average of exons in DNA is from 5 to 8
there may be 13 or 2 but the average (mainly)
is 5-8 {variable not stable}
• Only 2% of DNA will go through translation
(functional), 98% (nonfunctional) DNA
• Cell cycle has 3 phases G1, G2, and S phase
(synthesis) in which replication occur
• Interphase has G1 phase, S phase, and G2
phase
• Mitotic phase which is sex phase
• Cytokenises in which cell division will take
place, if the G1 is cell mature it goes into gap
zero this means that the cell will be going
through apoptosis (death)
• In Sphase without DNA replication there is no
cell division, the cell will wait for the DNA to
replicate because there is no logic for cell
division without the replication of DNA, DNA
has to go through both daughter cells
• From {in human S period……….20 hrs}
This is why we have multiple origin of replication
• Not all replicants are necessary to be replicated
at the same time
• DNA polymerase σ functions (similar) like DNA
polymer III in prokaryotes
• ssDNA-binding protein single stranded
binding protein
responsible for unwinding of helix to create
two replication forks so they would not rejoin
• Leading strand synthesis
polymerase alpha is responsible for RNA
primer
• In telomere the cells will replicate up to a
certain limit, there is something called hestic
hayflick theory that says that cells cant divide
infinitely it has limited number of replication
because every time we will see that there is
shortening for the chromosomes
• Telomerase that are found at the ends of the
chromosome to protect the chromosome from
joining and to be separated so each strand would
be responsible for a specific function
• The end of chromosome telomerase make t-loop
and goes back to the chromosome itself and they
may make some problems in DNA
• The leading strand has one primer that gets
removed and its complete but in laging strand
each time a primer gets removed and join
together this causes a gap to occur which is
primer gap, primer gap cannot be filled by
ordinary DNA polymerase this problem does no
undergo the leading strand
• In first replication the we will have one short
chromosome then the same DNA undergo
through the second round we will have one
chromosome shorter than the other
• Tolemerase enzyme adjust the life time of the
cell it gives indication of how many times the
cell can replicate and multiply
• Telomerase enzyme sees the G rich tail and use
its own bases to elongate the terminal ends of
the DNA, it adds nucleotide bases until it is
ready for polymerase lll to put new
nucleotides. At the end it will have a primer the
primer will be shorter
so the telomerase add units for the short
segments for the DNA polymerase lll to act
then elongation happens
• Cells die at the end because it gets telomer to
be shorter and shorter in each division
• Telomerase add units at original DNA to
increase DNA laging strand