DNA Synthesis Flashcards
What is the direction of DNA chain growth?
5’ to 3’
Where does DNA polymerase attach?
The 3’ end of the priming strand.
DNA primase
Synthesizes an RNA primer on lagging strand (10 nucleotides long).
How is the old RNA primer erased on a lagging strand?
By DNA polymerase, it just chews through it.
When does the synthesis of each okazaki fragment end?
When DNA polymerase runs into the RNA primer attached to the 5’ of the previous fragment.
DNA ligase
Joins 3’ end of new DNA fragment to the 5’ end of the previous, uses ATP
DNA helicase
Hydrolyzes ATP when bound to single stranded DNA.
Single stranded binding proteins
Prevent formation of short hairpin helices.
Sliding clamp
Keeps DNA polymerase bound until it reaches a sequence of double stranded DNA.
What is the purpose of the clamp loader?
Assembles the sliding clamp and DNA polymerase by ATP hydrolysis. It releases when DNA polymerase binds.
DNA topoisomerase
Reversible nuclease that adds itself covalently to a DNA backbone and breaks the phosphodiester bond. Creates a relative state of negative super coiling.
Topoisomerase I
Acts even when no DNA replication is occuring, cuts one strand.
How does all DNA synthesis begin?
With an RNA primer.
Topoisomerase II
Cuts two strands, creates a protein “gate”
When can eukaryotes perform DNA replication?
During the S phase.
