1. 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 4X that of E. coli •Drosophila 100X that of E. coli
•Solution:
Multiple replication origins
•Yeast replicons •Mammalian cells up to 25,000

2. DNA Synthesis in Eukaryotes
Pre-initiation replication complex:
ORC
Cdt1
Cdc6
MCM

3. Comparison of some replication components
Enzyme Function
Prokaryotes
Eukaryotes
Helicase
Primase
Polymerase
Proofreading
Sliding clamp
Prevent ss closure
DnaB
DnaG
Pol III
b sliding clamp
SSBPs
MCM
Primase s.u. of a-polymerase
Pol d and e
PCNA (Proliferating Cell Nuclear Antigen)
RPA (Replication Protein A)

4. A Problem and a Solution

5. Telomere Formation

6. The Damage and Repair of DNA
Two main types of DNA damage:
*point mutations
*structural changes
The molecular basis of point mutations
1. Base substitution (mismatches)
transition
transversion
2. Tautomeric shift

7. Gene Mutation The molecular basis of point mutations
3. Base analogs and chemical mutagens

8. DNA Damage The molecular basis of structural damage
1. Hydrolytic damage
Deamination
N-glycosidic bond – very weak and easily broken
Depurination
Deamination

9. DNA Damage
The molecular basis of structural damage
2. Alkylation

10. DNA Damage The molecular basis of structural damage
3. Oxidation and Radiation