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DNA andDNA and
ReplicationReplicationcopyright cmassengale
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HistoryHistory
of DNAof DNA
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History of DNA
• Early scientists thoughtprotein was the cell’s
hereditary material becauseit was more complex thanDNA
• Proteins were composed of 2different amino acids in longpolypeptide chains
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!ransformation!ransformation
• "red #riffith wor$ed with%irulent & and non%irulent R strain Pneumoccocus bacteria
• He found that R strain couldbecome %irulent when it too$ inDNA from heat'$illed & strain
• &tudy suggested that DNA wasprobably the genetic material
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#riffith Experiment
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History of DNA
• (hromosomes are madeof both DNA andprotein
• Experiments onbacteriophage %irusesby Hershey ) (hase
pro%ed that DNA wasthe cell’s geneticmaterial
Radioacti%e *2P was in+ected into bacteria, copyright cmassengale
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Disco%ery of DNADisco%ery of DNA
&tructure&tructure• Erwin (hargaff showed theamounts of the four bases on
DNA - A.!.(.#/• 0n a body or somatic cell1 A *3*4
! *3*4 # 56374 ( 56364
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(hargaff’s Rule(hargaff’s Rule
• AdenineAdenine must pair with!hymine!hymine
• #uanine#uanine must pair with
(ytosine(ytosine• !he bases form wea$hydrogen bonds
# (! A
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DNA &tructureDNA &tructure
• Rosalind "ran$lin too$diffraction x'ray
photographs of DNAcrystals
• 0n the 567’s. 8atson )
(ric$ built the first model of DNA using "ran$lin’s x'rays
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Rosalind "ran$linRosalind "ran$lin
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DNADNA
&tructure&tructure
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DNADNA• !wo strands coiled calleda double helix
• &ides made of a pentosesugar Deoxyribose bondedto phosphate -P9:/ groupsby phosphodiester bonds
• (enter made of nitrogenbases bonded together bywea$ hydrogen bonds
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DNA Double HelixDNA Double Helix
NitrogenousNitrogenous;ase -A.!.# or (/;ase -A.!.# or (/
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HelixHelix
• ?ost DNA has a?ost DNA has a right'handright'hand twist withtwist with 5 base pairs5 base pairs in ain acomplete turncomplete turn
• >eft twisted DNA is called>eft twisted DNA is called@'DNA@'DNA oror southpawsouthpaw DNADNA
•Hot spotsHot spots
occur where rightoccur where right
and left twisted DNA meetand left twisted DNA meet
producingproducing mutationsmutations
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DNADNA• &tands forDeoxyribonucleic acid
• ?ade up of subunits callednucleotidesnucleotides • NucleotideNucleotide made of1made of1
53 Phosphate groupPhosphate group23 7'carbon sugar7'carbon sugar*3 Nitrogenous baseNitrogenous base
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DNA NucleotideDNA Nucleotide
9P'9 9
PhosphatePhosphate #roup#roup
NNitrogenous baseNitrogenous base -A. #. (. or !/-A. #. (. or !/
(H2
9
(5(:
(* (2
7
&ugar&ugar-deoxyribose/-deoxyribose/
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Pentose &ugarPentose &ugar
• (arbons are numbered cloc$wise 5’to 7’
(H2
9
(5
(:
(* (2
7
&ugar&ugar-deoxyribose/-deoxyribose/
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DNA1DNA1 &trands are Antiparallel&trands are Antiparallel
P
P
P
9
9
9
5
2*
:
7
7
*
*
7
P
P
P
9
9
9
5
2 *
:
7
7
*
7
*
# (
! A
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A Polynucleotide
• MANYnucleotides
(“links”)bondedtogetherDNA has a
overall
negativecharge b/c of
the PO4-3
(phosphate
group)
Ph h di B d
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• Phosphodiester Bond
–The covlenttht holdstogether thebckbone
–!ound bet"eenP # deo$yribosesugr
–%T&'N
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Antiparallel &trandsAntiparallel &trands
• 9ne strand ofDNA goes from7’ to *’ -sugars/
• !he otherstrand isopposite in
direction going*’ to 7’ -sugars/
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Nitrogenous ;asesNitrogenous ;ases
• Double ringDouble ring PR0NE&PR0NE&
Adenine -A/Adenine -A/
#uanine -#/#uanine -#/
• &ingle ring&ingle ring PBR0?0D0NE&PBR0?0D0NE&
!hymine -!/!hymine -!/(ytosine -(/(ytosine -(/ ! or (
A or #
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;ase'Pairings;ase'Pairings
• Purines only pair with Pyrimidines
• !hree hydrogen bonds
reCuired to bond #uanine) (ytosine
(#
* H'bonds
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! A
•!wo hydrogen bonds arereCuired to bond Adenine )!hymine
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uestion1uestion1
• 0f there is *4
AdenineAdenine. how much(ytosine(ytosine is present
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Answer:Answer:
• !here would be 24(ytosine(ytosine
• Adenine -*4/ !hymineAdenine -*4/ !hymine-*4/-*4/• #uanine -24/ (ytosine#uanine -24/ (ytosine
-24/-24/• !herefore.!herefore. F4 A'! andF4 A'! and:4 ('#:4 ('#
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DNADNA
ReplicationReplication
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Replication "actsReplication "acts
• DNA has to be copiedDNA has to be copiedbefore a cell di%idesbefore a cell di%ides
• DNA is copied during theDNA is copied during the && or synthesis phase ofor synthesis phase ofinterphaseinterphase
• New cells will needNew cells will need identicalidenticalDNA strandsDNA strands
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&ynthesis Phase -& phase/&ynthesis Phase -& phase/
• & phase during interphase of thecell cycle
• Nucleus of eu$aryotes
?itosis'prophase'metaphase'anaphase
'telophase
#5 #2
&phase
interphase
DNA replication ta$esDNA replication ta$esplace in the & phase3place in the & phase3
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DNA ReplicationDNA Replication•
;egins at;egins at
9rigins of Replication9rigins of Replication
• !wo strands open forming!wo strands open forming ReplicationReplication"or$s -B'shaped region/"or$s -B'shaped region/
• New strands grow at the for$sNew strands grow at the for$s
ReplicationReplication"or$"or$
Parental DNA ?oleculeParental DNA ?olecule
*’
7’
*’
7’copyright cmassengale
• Chain elongation occurs in the 5' to3' direction by addition of onenucleotide at a time to the 3' end
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• As replication for!
"oves# onl$ % stran&can serve aste"plate forcontinuous *NA
synthesis'the leding strnd
• Opposite lgging
strnd un&ergoesdiscontinuous *NAsynthesis+
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DNA ReplicationDNA Replication
• As the 2 DNA strands open atAs the 2 DNA strands open atthe origin.the origin. Replication ;ubblesReplication ;ubbles formform
• Pro$aryotes -bacteria/ ha%e asingle bubble
• Eu$aryotic chromosomes ha%e?ANB bubbles
;ubbles ;ubbles
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• DNA replication
begins at the origino, repliction an& isbidirectionl ratherthan unidirectionl+
• A replicon is thelength of DNA that isreplicate& folloingone initiation event
at a single origin
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DNA ReplicationDNA Replication
• EnGymeEnGyme HelicaseHelicase unwindsunwindsand separates the 2 DNAand separates the 2 DNAstrands by brea$ing thestrands by brea$ing the
wea$ hydrogen bondswea$ hydrogen bonds• &ingle'&trand ;inding&ingle'&trand ;indingProteinsProteins attach and $eep
the 2 DNA strandsseparated and untwisted
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DNA ReplicationDNA Replication
• EnGymeEnGyme !opoisomerase!opoisomerase attachesto the 2 for$s of the bubble torelie%e stressrelie%e stress on the DNADNA
moleculemolecule as it separatesEnGyme
DNA
EnGyme
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DNA ReplicationDNA Replication
• ;efore;efore new DNA strands canform. there must be RNARNAprimersprimers present to start the
addition of new nucleotides• PrimasePrimase is the enGyme that
synthesiGes the RNA Primer
• DNA polymerase can then addthe new nucleotides
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DNA ReplicationDNA Replication
• DNA polymeraseDNA polymerase can only addcan only addnucleotides to thenucleotides to the *’ end*’ end of theof theDNADNA
• !his causes the!his causes the NE8NE8 strand to bestrand to bebuilt in abuilt in a 7’ to *’ direction7’ to *’ direction
RNARNAPrimerPrimerDNA PolymeraseDNA PolymeraseNucleotideNucleotide
7’
7’ *’
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&ynthesis of the New DNA&ynthesis of the New DNA&trands&trands
• !he!he >eading &trand>eading &trand issynthesiGed as a single strandsingle strandfrom the point of origin towardthe opening replication for$
RNARNAPrimerPrimerDNA PolymeraseDNA PolymeraseNucleotidesNucleotides
*’7’
7’
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&ynthesis of the New DNA&ynthesis of the New DNA&trands&trands
• !he!he >agging &trand>agging &trand isis synthesiGeddiscontinuouslydiscontinuously against o%erall direction ofreplication
• !his strand is made in ?ANB short segments 0t is replicated from the replication for$toward the origin
RNA PrimerRNA Primer
>eading &trand>eading &trand
DNA PolymeraseDNA Polymerase
7
’7’
*’
*’
>agging &trand>agging &trand
7’
7’
*’
*’ copyright cmassengale
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• DNA s$nthesis at a single replication
for!
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• *oth DNA stran&s are s$nthesi+e&
concurrentl$ b$ looping the laggingstran& to invert the ph$sical but notbiological &irection of s$nthesis
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>agging &trand &egments>agging &trand &egments
• 9$aGa$i "ragments9$aGa$i "ragments '' series ofshort segments on the lagginglaggingstrandstrand
• ?ust be +oined together by an?ust be +oined together by anenGymeenGyme
>agging &trand
RNARNA
PrimerPrimer
DNADNAPolymerasePolymerase
*’
*’
7’
7’
9$aGa$i "ragment9$aGa$i "ragment
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oining of 9$aGa$i "ragmentsoining of 9$aGa$i "ragments
• !he enGyme!he enGyme >igase>igase +oins the +oins the9$aGa$i fragments together to9$aGa$i fragments together to
ma$e one strandma$e one strand
>agging &trand
9$aGa$i "ragment 29$aGa$i "ragment 2
DNA ligaseDNA ligase
9$aGa$i "ragment 59$aGa$i "ragment 5
7’
7’
*’
*’
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Replication of &trandsReplication of &trands
Replication"or$
Point of 9rigin
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Proofreading New DNAProofreading New DNA
• DNA polymerase initially ma$esDNA polymerase initially ma$esaboutabout 5 in 5.5 in 5. base pairingbase pairing
errorserrors• EnGymesEnGymes proofread and correctproofread and correctthese mista$esthese mista$es
• !he new error rate for DNA that!he new error rate for DNA thathas been proofread ishas been proofread is 5 in 5 billion5 in 5 billion base pairing errorsbase pairing errors
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d l f& i i ? d l f
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&emiconser%ati%e ?odel of&emiconser%ati%e ?odel ofReplicationReplication
• 0dea presented by0dea presented by 8atson ) (ric$8atson ) (ric$
• !he!he two strands of the parentalmolecule separate. and each acts as a
template for a new complementarystrand
• New DNA consists of 5
PAREN!A> -original/ and 5 NE8strand of DNAParental DNA
DNA !emplate
New DNA
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• 3 possible "o&esof DNA replicationare possible
– conservative
– se"iconservative
– &ispersive
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DNA Damage ) RepairDNA Damage ) Repair
• (hemicals ) ultra%iolet radiation damage the DNA in our body cells
• (ells must continuously repairDA?A#ED DNA
• Excision repair occurs when any ofo%er 7 repair enGymes remo%edamaged parts of DNA
• DNA polymerase and DNA ligase replace and bond the new nucleotidestogether
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uestion1uestion1
• 8hat would be thecomplementary DNA
strand for the followingDNA seCuence
DNA 7’'(#!A!#'*’DNA 7’'(#!A!#'*’
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Answer1Answer1
DNA 7’'(#!A!#'*’DNA 7’'(#!A!#'*’
DNA *’'#(A!A('7’DNA *’'#(A!A('7’
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