GMan Chp15 - Replication initiation

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Exception to Watson and Crick's semiconservative replication?

Displacement replication
Where does displacement replication occur?
- Small, circular genomes
- Animal mtDNA and phages (lambda)
D-Loop

Site where dsDNA is interrupted by a primer (between the strands)
Which strand is copied first in displacement replication?

The displaced one
Types of displacement replication
- D-Loop
- Rolling circle
How does rolling circle replication begin?

A single strand is nicked
Rolling circle replication
- Take a good look at this
Advantages of rolling circle replication

Multiple copies produced rapidly
(continuous of discontinuous)
DNA synthesis is _____ at the 5' end
DNA synthesis is _____ at the 3 end

DNA synthesis is continuous at the 5' endDNA synthesis is discontinuous at the 3 end using RNA primers
Stages of DNA replication

Initiation, Elongation, Termination
Where does DNA replication begin?

Origin(s) of replication
Replication bubble

Separated DNA strands in DNA replication
Overall DNA replication is ____
What direction?

Bidirectional
Replication fork
- Y-shaped region where new DNA strands are elongating
- Point where DNA strands separate to form a replication bubble
Helicases

Melt the dsDNA at the replication fork
Single stranded binding proteins

Bind and stabilize the ssDNA
Topoisomerases

Ease tension ahead of the replication fork(s) by introducing nicks
Primase

Introduces the RNA primer used to initiate DNA synthesis
Origin of replication in e.coli
- OriC
- ~245 Bp long
Structure of OriC
- ~245 Bp
- Two short repeating motifs:
- i. 9nt segments (DnaA binding)
- ii. 13nt segments (Zone of melting)
DnA A binding to OriC
- The DnaA complex interacts with the 9nt repeats of OriC
- This interaction causes the 13nt (AT) regions (ATP Hydrolysis) to denature (melt)
- SSBs and DnaB are introduced
Structure of the OriC 13nt nucleotides
- AT Rich
- Fewer hydrogen bonds make easier melting
How does DnaB bind
- Initially attached to DnaC
- Binds melted 13nt (AT) regions along with SSBs
- DnaC is released
Structure of DnaA

30 Monomer subunits
How many DnaB/DnaB complexes load onto the replication bubble?

Siz
Why is dnaC important?

Aids proper loading of DnaB
What is the helicase in the prepriming complex?

DnaB
How do SSBS stabillize ssDNA
- Prevent re annealing of melted DNA (by DnaB)
- Protect against nuclease activity
Steps of initiation that use ATP
- Melting 13nt (AT) regions after DnaA binding
- DnaB/DnaC binding
Structure of SSBs
- Homotetramers
- Bind to DNA in a series
Conversion from Prepriming to Priming complex
- DnaB (DNA Helicase) recruits the primase
- Primer synthesis occurs
β-subunit clamp
- Loads after the primer is created
- Preceeds DNA Pol III loading and elongation

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GMan Chp15 - Replication initiation

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GMan

Updated

2017-03-02T21:52:38Z

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