Textbook – Many proteins work together in DNA Replication and Repair
The Basic Principle: Base Pairing to a Template Strand:
•
Complementary strands, antiparallel to each other
•
Each strand serves as a template for ordering nucleotides into another complementary
strand
•
Semiconservative Model – When a double helix replicates, each of the 2 daughter
molecules will have one old strand (from parent) and one new strand
- Proposed by Watson & Crick
•
Conservative Model – 2 parent strands come back together and daughter molecules
form new helix
•
Dispersive Model – All 4 strands of DNA after replication have a mixture of new & old
DNA
•
Matthew Meselson & Franklin Stahl (1958) – proved that semiconservative model is
correct
*Grew E. coli in a medium containing labeled 15N (heavy nitrogen) for several
generations, then transferred to medium containing 14N (light nitrogen)
*They took 2 samples from the culture; 1 after 1
st
replication, another after 2
nd
*Centrifuged samples
- 1
st
sample: got a hybrid band; told them it wasn’t conservative model
- 2
nd
sample: both light DNA & hybrid bands; told them it wasn’t dispersive
“Getting Started”:
•
Replication of DNA begins at sites called origins of replication (short stretches of DNA
having a specific sequence of nucleotides)
•
The E. coli chromosome is circular and contains 1 origin
•
Proteins that initiate replication recognize the sequence and attach to the DNA,
separating the 2 strands and opening a replication “bubble”
•
Replication proceeds in both directions until the entire DNA is copied (in E. coli)
•
Eukaryotic chromosomes have 100s-1000s of origins and replication also proceeds in
both directions from the origin
•
At the end of the bubble is a replication fork (Y-shaped region where parental strands
are unwound)
•
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- '08
- GILBERT
- Biology, DNA, Proteins, DNA Damage, new DNA strand, DNA pol, DNA replication complex
-
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