DNA Replication
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Transcript of DNA Replication
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DNA Replication
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Structure of DNA• Watson & Crick
– developed double helix model of DNA• other leading scientists working on question:
– Rosalind Franklin
– Maurice Wilkins
– Linus Pauling
1953 | 1962
Franklin Wilkins Pauling
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Watson and Crick1953 article in Nature
CrickWatson
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Rosalind Franklin (1920-1958)
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Double helix structure of DNA
“It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.”Watson & Crick
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Semiconservative DNA Replication
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Base pairing in DNA• Purines
– adenine (A)– guanine (G)
• Pyrimidines– thymine (T)– cytosine (C)
• Pairing– A : T
• 2 bonds
– C : G• 3 bonds
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Copying DNA• Replication of DNA
– base pairing allows each strand to serve as a template for a new strand
– new strand is 1/2 parent template & 1/2 new DNA
• semi-conservative copy process
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Replication: 1st step• Unwind DNA
– helicase enzyme unwinds part of DNA helix
replication fork
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DNAPolymerase III
Replication: 2nd step
Build daughter DNA strand add new complementary
bases Wih the help of DNA
polymerase III
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Fast & accurate!• It takes E. coli <1 hour to copy
5 million base pairs in its single chromosome – divide to form 2 identical daughter cells
• Human cell copies its 6 billion bases & divide into daughter cells in only few hours– remarkably accurate– only ~1 error per 100 million bases– ~30 errors per cell cycle
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What does it really look like?
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Transcription
fromDNA nucleic acid language
toRNA nucleic acid language
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How Are Different Types of Cells Created and Maintained?
By differential gene expression.
The same genetic information is in all 100 trillion cells of any one person. Different cells use the same blueprint in different ways.
How?
by regulating the flow of information from DNA to protein.
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2005-2006
RNA• ribose sugar
• N-bases– uracil instead of
thymine– U : A– C : G
• single stranded
RNADNAtranscription
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RNA
RNA is a nucleic acid that uses a different sugar than DNA and the base uracil (U) in place of thymine (T).
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RNA Is Single-Stranded which allows it to travel in and out of the nucleus
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There are Different RNAs with Distinct Functions
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Matching bases of DNA & RNA
• Match RNA bases to DNA bases on one of the DNA strands
U
A G GGGGGT T A C A C T T T T TC C C CA A
U
UU
U
U
G
G
A
A
A C CRNA polymerase
C
C
C
C
C
G
G
G
G
A
A
A
AA
5' 3'
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Transcription
The enzyme RNA polymerase opens the DNA strands and synthesizes an RNA complementary to only one of the DNA strands.
RNA polymerase acts here
RNA polymerase
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Transcription
The decision to transcribe a gene is the most important step in the control of gene expression.
Transcription starts and stops at distinct sites at the ends of a gene.
A gene
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The “Central Dogma”• Flow of genetic information in a cell
– How do we move information from DNA to proteins?
transcription
translation
replication
proteinRNADNA trait
DNA gets all the glory, but proteins do all the work!
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mRNA
From gene to protein
DNAtranscription
nucleus cytoplasm
aa
aa
aa
aa
aa
aa
aa
aa
aa
aa
aa
proteintranslation
ribosome
trait
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2007-2008
Any Questions??