DNA Replication and Fidelity
2 Major Activities- Strand Separation, DNA synthesis
Strand Separation- Unwinding proteins/Helicase unwinds DNA, Helix destabilising proteins (allows replication and prevents recoiling)
Gyrase- cause break in DNA strand which coils it back on itself allows access for replication
DNA Synthesis- Polymerase activity, only add base in 5' to 3' direction one base at a time, primer essential
Primer- region of double strandedness, RNA Polymerase = primase
Discontinuos synthesis (Lagging Strand)- antiparrallel strands, one strand starts and stops, OKAZAKI FRAGMENTS produced, primers have to be removed, DNA Polymerase 3 fills in the gaps. At least 1 strand is discontinuous!
DNA Ligase covalently bonds OKAZAKI Fragments and fill primer spaces!
Replication Origins- molecular signal, where they occur varies
Teleomeres- replication at 5' end of bases, no primer to complete DNA, reverse transcriptase adds RNA Primer to maintain length
Circular = No ENDS, to replicate nuclease cuts and nucleotide added to 3' end replicated in direction of rolling, other strand is discontinuous.
Tautomerise- different isomer of base! 2 forms of each of the bases keto=Normal, Enol=Rare Spontaneous mutations can be caused by tautomers.
2 Mechanisms to maintain Fidelity- Error Avoidance, Error Correction Error Avoidance- Complementary base pairing, Selective binding of Polymerase checking for correct base
Error Correction- Post synthetic and mismatch repair (mutS mutH mutL DNA polymerase 1 and polynucleotide ligase required)