DNA Synthesis•Eukaryotes
•DNA unwinds at a replication origin •Two replication forks form •Bidirectional synthesis of DNA •Much more DNA; complexed with proteins
•Eukaryotes have much more DNA
•Yeast 250-400 replicons •Mammalian cells up to 25,000
•Solution: Multiple replication origins
•Yeast 4X that of E. coli •Drosophila 100X that of E. coli
DNA Synthesis in Eukaryotes
Pre-initiation replication complex:ORCCdt1Cdc6MCM
Enzyme Function
Prokaryotes Eukaryotes
Helicase
Primase
Polymerase
Proofreading
Sliding clamp
Prevent ss closure
DnaB
DnaG
Pol III
Pol III
b sliding clamp
SSBPs
MCM
Primase s.u. of a-polymerase
Pol d and e
Pol d and e
PCNA (Proliferating Cell Nuclear Antigen)
RPA (Replication Protein A)
Comparison of some replication components
A Problem and a Solution
Telomere Formation
The Damage and Repair of DNA
The molecular basis of point mutations1. Base substitution (mismatches)
transitiontransversion
Two main types of DNA damage:
*point mutations*structural changes
2. Tautomeric shift
3. Base analogs and chemical mutagens
Gene MutationThe molecular basis of point mutations
DNA DamageThe molecular basis of structural damage1. Hydrolytic damage
N-glycosidic bond – very weak and easily broken
Deamination
Deamination
Depurination
DNA DamageThe molecular basis of structural damage
2. Alkylation
DNA DamageThe molecular basis of structural damage3. Oxidation and Radiation
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