DNA replication Flashcards
What is the difference between meiosis and mitosis?
Mitosis - 2 daughter cells produced
Meiosis - 4 gametes produced
What are the divisions of interpahse in the cell cycle?
G1 - preperation for replication
S - DNA replication
G2 - Cell grows in size
During which stage does DNA replication occur?
Interphase - S phase
What are the 3 theories for DNA replication
Conservative replication
Semi-conservative replication
Dispersive replication
Describe the conservative model for DNA replication
Entirely new double strand of DNA is made
Over time the N15 strand becomes a decreasing fraction of the population
Describe the semi-conservative model for DNA replication
1 strand is synthesised and 1 strand is passed on - original parental strands are split over 2 daughter strands
Describe the dispursive model for DNA replication
Parental DNA is divided between each new daughter strand during every replication
What enzymes are needed for semi-conservative replication?
Topoisomerase - unwinds double helix and cuts the chain
Helicase - unwinds double helix
DNA pol III - travels from 5’ to 3’ joining nucleotides
DNA ligase - links toghether okozaki fragments are repairs cuts made by topoisomerase
Primase - a type of RNA polymerase that synthesises a 60 nucleotide long primer which begins DNA replication
DNA pol I - repairs DNA and removes primer
DNA pol II - repairs DNA
What direction does DNA Pol III travel in?
DNA pol III travels from 5’ to 3’. It synthesises base addition from the 3’ end of the primer. Because the strand are anti parallel, DNA pol will be travelling in opposite directions
What proteins are needed in semi-conservative replication?
Single strand binding proteins (SSB’s) - bind to single strands to prevent them re-annealing or binding to themselves
Sliding clamp - protein which holds DNA pol II on the strand
What substrates are needed in semi-conservative replication?
Deoxynucleotide triphosphates - dATP, dGTP, dCTP, dTTP
Ribonucelotide triphosphates - ATP, UTP, CTP, GTP
What is meant by replicon?
Single piece of DNA that replicates
What is meant by the origin?
Initiaition site where replication starts
Initiation proteins target the A-T rich origin - only 2H bonds need breaking
What is meant by the pre-replication complex?
Pre replication complex - unzips the double helix, creating the replication bubble
What is meant by replication bubble?
Replication bubble - structure formed when double strand is unzipped
What is meant by replication fork?
Replication fork - point where double strand separates
Describe the prokaryotic replicon
Prokaryotic chromosomes are circular - consist of a single replicon.
The terminus site is 180 degrees opposite the origin
Describe the eukaryotic replicon
Eukaryotic chromosomes are linear - have multiple replicons and origins
Step 1 of DNA replication
- Topoisomerase cuts strand at origin
- DNA helicase unwinds DNA to 2 single strands, creating a replication fork
- SSB’s coat strands to prevent re-annealing
Step 2 of DNA replication
- RNA primase synthesises a 60 nucleotide primer complementry to open chains
- Ribonucleotides in the primer bind to the each strand
Step 3 of DNA replication
- DNA Pol III and clamping proteins bind to the 3’ end of the primer
- DNA Pol III attaches deoxyribonucleotides to the 3’ end of the primer
- The clamping protein is released allowing DNA polymerase to slide to the 3’ end of another primer
Where does DNA Pol III attatch during DNA replication?
DNA Pol III attatches to the 3’ end of the primer
Can DNA polymerase initiate replication?
DNA Pol cannot innitate replication, it can only extend the strand. RNA PRIMASE INNITIATES REPLICATION
What does the release of the clamping proteins allow DNA polymerase to do?
The release of the clamping protein allows DNA Pol III to slide to the 3’ end of the next primer
