Chapter 12Chapter 12TopicsTopics

Models of Replication

Prokaryotic and Eukaryotic Replication

Models of Recombination: read pp 339-342

Three Models of DNA Replication Which is correct?

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DATA TO SUPPORT SEMI-CONSERVATIVE MODEL

Prokaryotic ReplicationProkaryotic Replication

Bacteria can double every 20 minutes at a rate of 1000 nucleotides/second!

E.coli 4.7 million bp

2 models of Prokaryotic 2 models of Prokaryotic ReplicationReplication

θθThe Theta Model The Theta Model

Rolling Pin ModelRolling Pin Model

Theta Replication

Radioactive labeled prokaryotic DNA

Rolling Pin Model

Occurs in viruses and factor F

Prokaryotic Mechanism of Prokaryotic Mechanism of ReplicationReplication

An: overview of E. coli replication

Animation of ElongationAnimation of Elongation

Nucleotide polymerization

http://www.johnkyrk.com/DNAreplication.html

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Bacterial Mechanism of Replication

Step 1. Initiation

Step 2. Unwinding: Helicase

oriC

helicases

Key concepts & Proteins

Notice: Replication Bubble Forms

Helper proteinsHelper proteins

Notice: Directionality

Step 4. Elongation

Step 3: Primase

Okazaki Fragments

Prokaryotes PolymerasesProkaryotes Polymerases

Pol l Pol l

Pol IIPol II

Pol IIIPol III

Pol IVPol IV Pol VPol V

The major players are:The major players are:

ELONGATION: step 4

repair

repair

Removes/replaces primers

Step 5. LigationStep 5. Ligation

LigaseLigase

These darn OkazakiFragments!

Step 6. TerminationStep 6. Termination

A certain A certain DNA sequenceDNA sequence may may replicationreplication

AA proteinprotein may physically replication may physically replication

Lagging strand

Leading strand

Prokaryotic DNA replicationSUMMARY

How How areare mistakes avoided? mistakes avoided?

By: Nucleotide selectionBy: Nucleotide selection

By: ProofreadingBy: Proofreading

By: Mismatch RepairBy: Mismatch Repair

Fidelity of DNA replicationFidelity of DNA replication

Only 1 mistake per billion nucleotides! Only 1 mistake per billion nucleotides!

Eukaryotic ReplicationEukaryotic Replication

A human chromosome about 100 million bp Replication occurs in minutes to hours!

Can you notice a difference between this replication process

vs bacterial replication?

Answer: Numerous replication origins.

Got it!

5’ to 3’ replication occurs in eukaryotes just like in our bacterial friends.

Prokaryotic and Eukaryotic Prokaryotic and Eukaryotic Replication are similar but Replication are similar but

there are some differences; there are some differences; these include…these include…

Origins “get tagged” by a replication licensing factor.

There are more and There are more and different DNA polymerases.different DNA polymerases.

Eukaryotic DNA PolymerasesEukaryotic DNA Polymerases

DNA Pol DNA Pol αα

DNA polDNA pol δδ

ß DNA pol DNA pol ββ

DNA pol DNA pol εε

DNA pol DNA pol γγ

Priming & replication Priming & replication (RNA (RNA polymerasepolymerase

ReplicationReplication

Repair & recombinationRepair & recombination

Repair and replicationRepair and replication

Mitochondrial DNA replicationMitochondrial DNA replication

Nucleosome Assembly Nucleosome Assembly

Unique to eukaryotic replication process

What happens when you reach What happens when you reach the end of linear DNA?the end of linear DNA?

Oops a problem at the end!!

Telomeres and Telomerase!Are loss of

telomeres related to aging?

Or is too much telomerase

activity related cancer?

Intestinal cells

Embryonic cells

Cells with telomerase activity

And bone marrow

Disease of Aging: Werner’s Disease of Aging: Werner’s DiseaseDisease

Related to mutated helicase; Why would this cause an error in DNA replication?

Assignment please read: pp Assignment please read: pp 339-342339-342

The Holliday Model of DNA recombination