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Midterm

Biology 1201A Study Guide - Midterm Guide: Dna Replication, Telomerase Rna Component, Spindle Apparatus
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3 pages97 viewsFall 2016

Department
Biology
Course Code
Biology 1201A
Professor
Vera Tai
Study Guide
Midterm

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Biology 1201 Test 1 Outcomes Part 3
Struture of a repliatio ule, with ezes, priers, sthesized DNA strads et…
In the replication bubble, the Ori is in the middle and you have 2 replication forks going in 2
different directions; in both of the directions, there will be a leading strand and lagging strand; if
on the left, the lagging strand is at the top and leading at the bottom, then on the right, the
lagging will be at the bottom and leading at the top
When the DNA helicase opens up the DNA, the direction of the strand stays the same on both
sides of the replication forks
On the leading strand, only 1 RNA primer is attached and then DNA polymerase III comes in and
adds DNA uleotides to the 3’-OH of the prier 5”-3” diretio
On the lagging strand, there are multiple RNA primers because the synthesis of DNA is occurring
in the opposite direction of the replication fork
It is possible to have one particular strand of DNA on a chromosome be replicated
continuously at side of the fork and discontinuously on the other side of the fork
Relationship between replicated DNA and metaphase chromosomes
o The relationship is that DNA needs to be perfectly replicated in order for it to reach the
metaphase of mitosis where it is able to line up in the middle caused by the mitotic spindles
o Replication needs to occur perfectly and the sister chromatids need to be present at the
metaphase of mitosis so that when the mitotic spindles pull apart the chromosome, there is
still a diploid number of chromosomes in both the new daughter cells each daughter cell
receives the exact number and type of chromosomes (genetic information) as the parent cell
before cell division
Reason why chromosomes shorten at each replication
Chromosomes shorten at each replication because at the end of the chromosomes, RNA
primers are removed and a gap is left over; now normally, the DNA polymerase III would come
i ad startig DNA uleotides  etedig eistig hai fro the 3” ed; HOWEVER, there
are no nucleotides in the exist chain because its at the end
This means the DNA polerase III a’t id to the DNA to add the uleotides ad therefore a
gap is left in the newly synthesized DNA
And then when that newly synthesized DNA becomes the parent strand, its new complementary
strand will become even shorter as more replications happen, the new strands will become
shorter and shorter this loss of DNA can have lethal consequences for the cell
Mechanism by which telomerase adds telomeres to chromosomes
o A telomere is a short DNA sequence that repeats many times and its length is maintained by
telomerase
o Since the DNA polerase III are ot ale to elogate the 3” ed of the ew strad eause
there no neighboring nucleotides to elongate, we have to increase the PARENT strand so that
primers can bind to it and DNA polymerase III can add nucleotides to it
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