What direction does bacterial dna replication occur
Bidirectional and from single origin
If relocation is unidirectional, termination and initiation will occur at the same site
What direction does eukaryotic Dna replication proceed
Bifurcation and from several fixed or digits
Forms advance until they meet another fork traveling in the same direction
Discuss DNA polymerase reaction
DNA polymerase catalyzes the nicleophillic attack by the 3’-OH
What substrates does DNA polymerase require
Dna template, an rna or dna primer and dNTPs
In addition DNA polymerase one has both 3’ and 5’ endonuclease activity
What is the major replicative polymerase in bacteria
DNA polymerase III
How does dna proofreading work
3’ exonucleolytic proofreading delays the extension from a mismatch allowing for duplex unwinding at the primer terminus, placing the mismatched 3’ nucleotide in the exonuclease site
Characteristics of DNA polymerase I
- 5’ to 3’
- 3’ exonuclease activity (proofreading)
- 5’ exonuclease activity (rna primer removal and dna repair)
- low polymerase processivity
Characteristics of DNA polymerase III
- 5’ to 3’ activity
- 3’ exonuclease activity (proofreading)
- High polymerase processivity
5 steps of dna replication involving discontinuous synthesis on the lagging strand
- Unwinding of parental duplex by helicase and elongation of leading strand by polymerase III expose single stranded region infront of lagging strand
- Primate synthesizes primer
- Polymerase 3 extends DNA Okazaki fragment from primer
- Polymerase I eliminates downstream rna primer by nick translation
- Dna Logan legates Okazaki fragment to rest of lagging strand
Action of e. Coli. Clamp loader
Exchange of ADP for ATP increases the affinity of the loader for the clamp
Upon binding the loader opens the clamp
Binding of the template primer dna to atp hydrolysis closure and clamp and release of loader
How does topoisomerase work in the termination of dna replication
Topoisomerase IV allows the duplicates circular dna to decatenage through 2 mechanisms
4 steps of extension of telomeres dna by telomerase
- Telomerase binds to hexanucleotide telomere sequence via complementarity with telomerase dna
- Telomerase reverse transcribed the hexanucleotide telomere tequence through incorporating dNTPs at the 3’-OH of telomere sequence
- Telomerase Carrie’s out rna templates dna synthesis
- Telomerase either translocated or dissociates and rebinds to post it Jon itself for a second round of nucleotide incorporation and the cycle repeats
Huntingtons disease
- autosomal dominant neurological disease
- brain protein Huntingtin contains stretch of glutamine residues
- normal = 6-31 CAG repeats
- diseased = 80
- number of repeats increases if dna product slips out forming a loop during replication
