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DNA Synthesis - PowerPoint PPT Presentation


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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:

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slide1

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 250-400 replicons •Mammalian cells up to 25,000

slide2

DNA Synthesis in Eukaryotes

Pre-initiation replication complex:

ORC

Cdt1

Cdc6

MCM

slide6

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

slide7

Gene Mutation

The molecular basis of point mutations

3. Base analogs and chemical mutagens

slide8

DNA Damage

The molecular basis of structural damage

1. Hydrolytic damage

Deamination

N-glycosidic bond – very weak and easily broken

Depurination

Deamination

slide9

DNA Damage

The molecular basis of structural damage

2. Alkylation

slide10

DNA Damage

The molecular basis of structural damage

3. Oxidation and Radiation