DNA Replication Flashcards
what does DNA look like in Eu vs Pro?
Format?
size?
Location?
Packaging?
Format- Eu is linear while Pro is circular
Size- Eu have much more DNA
Location-Eu in nucleus while Pro in cytoplasm
Packaging- Eu have extensive packaging due to histones while Pro have very little packaging
What is the mechanism of DNA replication
Semi-Conservative
half is orignal strand and half is new
What is the basic process of DNA replication
-Replication proceeds from several fixed origins of replication
Replication bubbles form at origin of replication
Replication proceeds in a bidirectional manner
Replication forks advance until they meet another fork traveling in the opposite direction
Origins are programmed to iniate replication at fixed times during mitosis (in S phase)
S phase is important cell replication control
what proteins are involved in DNA replication
In eukaryotes
-Helicase
-DNA polymerase alpha
-single strandbinding protein
-DNA polymerase delta and epsilon
-DNA topoisomerase
-RNase H
-DNA ligase
What are the proteins involved in DNA replication
In prokaryotes
-Helicase
-Primase
-single strand binding protein
-DNA polymerase III
-DNA topoisomerase
-DNA polymerase I
-DNA ligase
what is the function of topoisomerase
Prevents tension in DNA strand by creating small knicks in sugar phosphate backbone to release tensio so that there are 10 base pairs per turn
What is the function of Helicase
Helicase unwinds DNA by breaking H-bonds. It moves right in front of site replication.
what is the function of DNA polymerase III/delta and epsilon
It synthesises the leading and lagging strand.
What is the function of single stranded binding protein.
Prevents loose strands from joining back together by covering them
This prevents the bases from binding to other chemicals or back together.
What is the function of primase?
Primase creates RNA template for DNA to be built on top of.
What is the function of DNA Ligase?
It joins the phosphate backbone of the replaced primer with the replicated DNA.
What is the function of DNA polymerase/RNase H
It replaces RNA primer with DNA
What direction is DNA replicated?
It is replicated in the 5’->3’ direction
why is DNA replicated in such a specific direction?
DNA polymerase catalyses the nucleophillic attack by the 3’-OH of the sugar at the alpha-phosphate of the incoming nuclueotide base.
This forms a new phosphodiester bond and releases pyrophosphate
How is the RNA primer removed?
-The RNA primer must be removed and replaced with deoxynucleotides.
-This is accomplised by the exonuclease and polymerase activities of DNA polymerase I while in eukaryotes, primers are removed by RNase H and then DNA polymerase adds the DNA
-ligase then joins the gaps in the backbone.
What must occur prior to the replication fork in eukaryotic division?
in terms of packaging
The nucleosomes must disassociate from the parent strand as the replication fork approaches.
What are the differences in DNA replication in Pro vs Eu
No. of origin of replication
Rate of replication per second
Primary DNA polymerase
Roles of other polymerases
DNA packaging
Telomeres
-In Pro there is 1 and in Eu there are many origins of replication.
-Rate of replicatiom in Pro is 1000nu/sec while in Eu is 40-400nu/sec.
-Primary DNA Pol in Pro is III and in Eu is delta and epsilon
-Role of other pol in Pro and Eu is DNA repair
-DNA packaging in Pro is not extensive and in Eu is extensive
-Telomeres are only found in Eu
What are telomeres and what is their function?
-They are repetitive sequences of DNA found at the ends of chromosomes
-They protect chromisimes by preventing useful DNA from being left behind during replication.
-This occurs because the excision of the RNS primer at the end of a DNA strand leaves a gap that cannot be filled as there is no 3’ primer terminus for DNA pol to extend from.
what is the end replication problem?
-Everytime DNA is replicated, chromosomes get shorter
-This continues until all the telomeres have been used up.
-At this point the cell has to end it’s life or risk becoming cancerous
what is telomerase?
Telomerase is an enzyme that is able to replace telomere but is only found in ceryain cells like germ or stem cells.
Describe lagging strand synthesis
-The lagging strand must grow in the 3’-5’ direction towards the replication fork.
-However, DNA pol can only add nucloetides in the 5’-3’ direction and so a strand must be formed in short, continous fragments known as Okazaki fragments
-This occurs when DNA pol replicates DNA in between two primers in the 5’-3’ direction but the overall effect of replicating in discontinous fragments results in the strand being replicated in the 3’-5’ direction.
