DNA replication Flashcards
Role of Magnesium ions (Mg 2+)
Required for DNA polymerase activity
Zidovudine can:
-Prolong life in HIV infected individuals
-Reduce mother to baby transmission by more than 20%
Initiator proteins (DNaA protein)
Binds to origin of replication and breaks hydrogen bonds between bases
DNA helicase (DNaB)
Opens helix and binds primase to form primosome
Helicase inhibitor (DNaC)
Delivers helicase to DNA template
DNA primase
An RNA polymerase that synthesizes a RNA primer on the lagging strand to enable DNA polymerase to synthesize DNA strand
DNA polymerase I
Remove RNA primer and replace with DNA
DNA polymerase III
Synthesis of leading and lagging strands
Single stranded binding protein (ssb)
Binds to single stranded DNA in the replication bubble and prevents it from reannealing or forming secondary structure
How are the Okazaki fragments joined together
DNA ligase
Lagging strand synthesis
Each Okazaki fragment requires a separate primer
How is DNA polymerase III loaded and maintained on the single stranded DNA template, and unloaded when it reaches double stranded DNA
Clamp protein
Clamp protein
Tightly holds the DNA polymerase onto the template for synthesis of long templates (increases expressivity), and releases DNA pol when it stalls at a region of double stranded DNA
For a bacterial replication fork moving at 500 bp per second, the parental DNA helix ahead of the fork must rotate at 50 revolutions per minute. This generates positive supercoils ahead of the replication fork.
Swivel the DNA using Topoisomerase enzymes
DNA gyrase (type II topoisomerase)
This enzyme introduces negative supercoils into the DNA. This reduces the positive supercoils introduced by the opening of the DNA. Also aids in the separation of the DNA during replication and transcription.