DNA replication Flashcards
Which direction does synthesis occur?
5’ to 3’ end
Why is there a lagging strand and leading strand?
The DNA strands are oriented antiparallel to one another
What is needed in lagging strand synthesis?
- DNA primase
- DNA polymerase
- Ribonuclease H
- DNA polymerase part 2.
- DNA ligase
What do DNA ligase and helicase both require to work?
ATP
What are 2 diseases associated with mutations affecting RECQ helicase
Werner syndrome- progeria
Bloom syndrome- rare cancer syndrome
What protein helps expose the DNA strands in the replication fork?
Single stranded binding proteins SSTBs
What are DNA posiomerases?
Prevent DNA from becoming tangled during DNA replication
Type 1- nick and reseal 1 strand. No ATP
Type 1- nick and reseal both strands. ATP
What are the DNA sequences called that direct the initiation of DNA replication?
Replicators/Origins
Where are these sequences found in humans?
Near to LMNB2, Myc and HBB
What are the 2 phases in DNA replication?
- Replicator selection- formation of a pre-replicative complex- occurs in G1
- Origin activation- unwinding of the DNA & recruitment of DNA polymerase
What happens int the formation of a pre-RC?
Origin recognition complex (ORC) binds to the replicator sequence
Cdc6 and Cd+1 bind to ORC
Mcm2-7 binds as well- complete formation of preRC
What do high levels of Cdks in S phase do?
Activate pre existing preRCs but prevent the formation of new preRCs
How does telomerase prevent progressive shortening of the chromosomes?
Addition of TTAGGG repeats to the 3’-OH at each telomere
