MB - DNA Replication errors II Flashcards
What is the function of primase in DNA replication?
Responsible for synthesizing RNA primers
What are some features of primase? (2)
- It has no editing functions (no proof reading)
- Activity is increased in the presence of helicase and itself (co-operativity)
What are some features of the Single Stranded Binding Protein (SSB) in DNA replication? (4)
- Encoded by ssb gene
- Forms a tetramer
- Leaves bases exposed when bound
- Binds co-operatively to ssDNA
What is the function of the clamp loader? (2)
1) Binds β clamp proteins
2) Transfers the β clamp onto DNA at primer 3’ end
What are the first 4 steps of elongation? (Lagging Strand Synthesis)
1) As helicase unwinds the duplex, primase re-binds and synthesizes a new primer
2) A β clamp is added to the primer by the clamp loader
3) A Pol III core binds once enough ssDNA has emerged for the β clamp to reach it
4) Primer 1 bound, with correct polarity
- First Okazaki fragment starts
What are the last 4 steps of elongation?
5) DNA is pulled by helicase and Pol III
- The lagging strand loops out, picking up SSB
6) Okazaki fragment lengthens
- Lagging strand loop gets longer
7) First Okazaki fragment finished.
- Primase re-binds helicase, then adds a second primer
8) Pol III core and β clamp detach from DNA, releasing completed fragment
How is the editing and correction of the lagging strand carried out during DNA replication?
Pol I binds the end of the first Okazaki fragment and replaces the RNA with DNA.
- DNA ligase seals the nick
What prevents DNA replication forks from overshooting?
Ter and Tus
When does +ve supercoiling occur?
When there is no longer room for DNA gyrase to bind
What acts to decantenate the molecules?
Topoisomerase IV
Where does initiation occur in chromosomes?
OriC
