DNA replication is semi-conservative

F: Genetic Control

1 Introduction:1.1 Structure of DNA and RNA1.2 Base pairing1.3 DNA is the genetic material

2 DNA Replication:

3 Transcription: DNA to RNA:

4 Translation: mRNA to protein:4.1 Introduction4.2 The Genetic Code4.3 tRNAs4.4 Ribosomes4.5 Mechanism of translation

5 Mutations:

6 Conclusions and Overviews:

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Xavier DANIEL, Ph.D.A

F: Genetic ControlDNA Replication is semi-conservative

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Goals of this lesson

Watson and Crick’s notice

Three ways to replicate DNA ?

Evidence for a semi-conservative DNA replication

Summary

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The student can

Describe the semi-conservative DNA replication

Describe the evidence for the semi-conservative DNA replication

DNA Replication: Reminder !

Cell division requires replication of genetic material

Before (almost) each cell division, DNA is replicated

DNA replication occurs during the S phaseof the cell cycle

Each strand of the double-stranded DNA is used as a template

One double helix….. Two double helices

Each daughter cell owns - the same genetic material- the same genetic material as their parent cell



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Summary

Crick and Watson (1953)Nobel Prize Medicine1962


2 Watson and Crick’s notice

A / T

G / C

“It has not escaped our notice that the specific pairing we have

postulated immediately suggests a possible copying mechanism for the

genetic material”

Crick and Watson (1953)Nobel Prize Medicine1962


2 Watson and Crick’s notice

The semi-conservative modelAfter each replication, each double helix is made of

50% of old DNA 50% of new DNA


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Summary

Watson and Crick’s model = semiconservative replication

Two other models: the conservative model and the

dispersive model.


3 Three ways to replicate DNA ?

Old DNA

NewDNA

Conservative ?Dispersive ?Semi-conservative ?


3 Three ways to replicate DNA ?

Old DNA

NewDNA


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Summary

Which of the three models is right ?

Experiments in the late 1950s

Matthew Meselson and Franklin Stahl



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All DNA contains…15N ONLY

centrifugation



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New DNA is lighter than old DNAOld DNA 15N

NewDNA 14N

Parent moleculedsDNA Parent molecule

ssDNAParent molecule



ssDNA

New nucleotides

Parent moleculessDNA

New strandssDNA

Parent moleculessDNA

New strandssDNADenaturation

Addition of



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Summary

Original double helix

New strands

After each DNA Replication,Each double helix contains

One strand from the parent molecule

One newly made strand

“Semi-conservative”: KEEP 50%


5 Summary

DNA replication is semi-conservative

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