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LECTURE 1
Introduction to
DNA and RNA(Chapter 09)
Slides 1!"# $"% "%"'
On your own:Slides !$%# %9"$# "&!
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INTR6DUCTI6N
7 -enetics8 Stud o5 the structure 5unction
transission o5 *enes
7 6nl living organismshae *enes
7 To understand *enetics .e .ill start .ith the
4uestion8 :;hat is Li5e Characteristics shared ? all liin* 5ors ?ut not ?
nonliin* 5ors
2
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;hat is the role o5 DNA in li5e :Duh@a (A .heel out o5 @ilter)
> I /ad Trou?le in -ettin* to Solla Solle. (.here there arent anpro?les at least er 5e.)
LIFE (GENES)
(negative entropy)
UNIVERSE
(entropy)
3
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/o. does li5e 5i*ht entrop In5oration and ne*atie entrop
>Analo* s di*ital
7 Di55erent or*aniss hae di55erent *enes#
di55erent strate*ies 5or the surial o5 the *enes
and their transission to the net *eneration
7 Those *enes that ?uilt the ?est :surial
achines= are still .ith us toda7 The ast aGorit o5 *enes .ere lost
7 This is a ?lind undirected process
6
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,6LECULAR -ENETICS
7 Chapter 9 eaines the *enetic aterial in detail8olecular *enetics> The stud o5 DNA structure and 5unction at the
olecular leel
7 Recent draatic adances in techni4ues andapproaches hae *reatl epanded ourunderstandin* o5 olecular *enetics>And also o5 transission and population *enetics
7 To a lar*e etent our @no.led*e o5 *eneticscoes 5ro our @no.led*e o5 the olecularstructure o5 DNA and RNA
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921 IDENTIBICATI6N 6B DNA AS
T/E -ENETIC ,ATERIAL
7 To 5ul5ill its role the *enetic aterial ust eet
seeral criteria
> 12 In5oration8 It ust contain the in5oration necessarto a@e an entire or*anis
> !2 Transission8 It ust ?e passed 5ro parent to
o55sprin*
> $2 Replication8 It ust ?e copied7 In order to ?e passed 5ro parent to o55sprin*
> %2 Hariation8 It ust ?e capa?le o5 chan*es
7 To account 5or the @no.n phenotpic ariation in each species
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921 IDENTIBICATI6N 6B DNA AS
T/E -ENETIC ,ATERIAL
7 The data o5 an *eneticists includin*
,endel .ere consistent .ith these 5our
properties> /o.eer the cheical nature o5 the *enetic aterialcannot ?e identi5ied solel ? *enetic crosses
7 Indeed the identi5ication o5 DNA as the *enetic
aterial inoled a series o5 outstandin*eperiental approaches
> These .ill ?e eained net
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Brederic@ -ri55ith Eperients .ith
Streptococcus pneumoniae
7 -ri55ith studied a ?acteriu (pneumococci) [email protected] as Streptococcus pneumoniae
7 S. pneumoniaecoes in t.o strains
> SSooth7 Secrete a polsaccharide capsule
> 3rotects ?acteriu 5ro the iune sste o5 anials
7 3roduce sooth colonies on solid edia
> RRou*h7 Una?le to secrete a capsule
7 3roduce colonies .ith a rou*h appearance
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In 19!& -ri55ith conducted eperients usin* t.o
strains o5 S. pneumoniae8 tpe IIIS and tpe IIR
12 InGect ouse .ith lie tpe IIIS ?acteria ,ouse died
Tpe IIIS ?acteria recoered 5ro the ouses ?lood
!2 InGect ouse .ith lie tpe IIR ?acteria
,ouse suried No liin* ?acteria isolated 5ro the ouses ?lood
$2 InGect ouse .ith heat@illed tpe IIIS ?acteria ,ouse suried
No liin* ?acteria isolated 5ro the ouses ?lood
%2 InGect ouse .ith lie tpe IIR heat@illed tpe IIIS cells ,ouse died
Tpe IIIS ?acteria recoered 5ro the ouses ?lood
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!igure ".#
Living type S bacteria wereinjected into a mouse.
Mouse died
Deadtype S
Livetype R
Mouse died Mouse survived Mouse survived
Living type R bacteria wereinjected into a mouse.
Heat-killed type S bacteriawere injected into a mouse.
Living type R and heat-killedtype S bacteria were injectedinto a mouse.
Type S bacteria were isolatedfrom the dead mouse.
No living bacteria were isolatedfrom the mouse.
No living bacteria were isolatedfrom the mouse.
Type S bacteria were isolatedfrom the dead mouse.
(a) Live type S (b) Live type R (c) Dead type S (d) Live type R + dead type S
Afterseveraldays
Afterseveraldays
Afterseveraldays
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Afterseveraldays
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-ri55ith concluded that soethin* 5ro the dead
tpe IIIS ?acteria .as trans5orin* tpe IIR
?acteria into tpe IIIS /e called this process trans5oration
The su?stance that allo.ed this to happen .astered thetrans5oration principle -ri55ith did not @no. .hat it .as
Su**ested that the *enetic in5oration olecule is
resistant to hi*h teperature ,ost proteins de*rade at hi*h teperature
Connect -ri55iths eperient to Eperient 1 (la?)
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;e no. @no. that the 5oration o5 the capsule is
*uided ? the ?acterias *enetic aterial
Trans5ored R ?acteria acquireda *ene 5ro the deadlsed S ?acterua that directs the cell ho. to a@e a
capsule polsachharide
Variationeists in a?ilit to a@e capsule (R cells carr a
non5unction allele 5or the *ene) The *ene re4uired to create a capsule is replicatedand
transmitted5ro other to dau*hter cells
6nce R cells ac4uired it the passed the trait to their
:o55sprin*= The olecular nature o5 the trans5orin* principle
.as deterined usin* eperiental approaches
that incorporated arious ?iocheical techni4ues14
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The Eperients o5
Aer ,acLeod and ,cCart
7 Aer ,acLeod and ,cCart realied that -ri55ithso?serations could ?e used to identi5 the *enetic aterial
7 The carried out their eperients in the 19%0s
> At that tie it .as @no.n that DNA RNA proteins andcar?ohdrates are the aGor constituents o5 liin* cells
7 The prepared cell etracts 5ro tpe IIIS cells and puri5iedeach tpe o5 acroolecule> 6nl the etract that contained puri5ied DNA .as a?le to conert
tpe IIR ?acteria into tpe IIIS
> Treatent o5 the DNA etract .ith RNase or protease did noteliinate trans5oration
> Treatent .ith DNase did
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!igure ".$
Aer et al.conducted the 5ollo.in* eperients To 5urther eri5 that DNA and not a containant (RNA
or protein) is the *enetic aterial
Mix Mix Mix Mix
Type R
cells
Type R
cells
Type S
DNAextract
Type R
cells
Type S
DNAextract+
DNase
Type R
cells
Type S
DNAextract+
RNase
Type R
cells
Type S
DNAextract+
protease
Transformed Transformed Transformed
1 2 3 4 5
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Allow sufficient time for the DNA to be taken up by the type R bacteria. Only a small percentage of the type R bacteria will be transformed to type S.
Add an antibody that aggregates type R bacteria (that have not been transformed). The aggregated bacteria are removed by gentle centrifugation.
Plate the remaining bacteria on petri plates. Incubate overnight.
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Head
Tail fiber
Base plate
Sheath
DNA(inside thecapsid head)
Eperient 9A /ershe and Chase
Eperient .ith Jacteriopha*e T!7 In 19"! Al5red /ershe and ,arsha Chase
proided 5urther eidence that DNA is the *enetic
aterial
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The studied the
?acteriopha*e T!
It is relatiel siplesince its coposed o5
onl t.o
acroolecules DNA and protein
!igure ".%
,ade upo5 protein
Inside the
capsid
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!igure ".&
Life cycle of
bacteriophage T2
Phage binds to host cell.
Capsid
Bacterialchromosome
Bacterialcell wall
Phage injects itsDNA into host cell.
The expression ofphage genes leadsto the synthesis of
phage components.
Phage componentsare assembled.
Host cell lysesand new phagesare released.
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Genetic material
3ha*e coat (protein)
precariousl attached
to ?acterial cell
DNA inside o5 cell
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7 The /ershe and Chase eperient can ?e
suaried as 5ollo.s8
> Used radioisotopes to distin*uish DNA 5ro proteins
7 $!3 la?els DNA speci5icall
7 $"S la?els protein speci5icall
> Radioactiella?eled pha*es .ere used to in5ect
nonradioactie Escherichia colicells
>A5ter allo.in* su55icient tie 5or in5ection to proceed
the residual pha*e particles .ere sheared o55 the cells
7 K 3ha*e *hosts and E. colicells .ere separated
> Radioactiit .as onitored usin* a scintillation
counter
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The /pothesis
> 6nl the *enetic aterial o5 the pha*e is inGectedinto the ?acteriu
7 Isotope la?elin* .ill reeal i5 it is DNA or protein
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Testin* the /pothesis
Re5er to Bi*ure 92"
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!igure ".' Copyright The McGraw-Hill Companies, Inc. Permission required or reproduction or display
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E$perimental level %on&ept"al level
Grow bacterial cells. Divide intotwo fasks.
1.
Into one fask add 35!"labeled #$a%e& int$e second fask add 32'"labeled #$a%e.
2.
(llow in)ection to occ*r.3.
(%itate sol*tions in blenders )ordi+erent len%t$s o) ti,e to s$ear t$ee,#t- #$a%es o+ t$e bacterial cells.
4.
entri)*%e at 10000 r#,.5.
/$e $eav- bacterial cells sedi,ent to t$e
#ellet w$ile t$e li%$ter #$a%es re,ain int$e s*#ernatant. !ee (##endi )ore#lanation o) centri)*%ation.
6.
o*nt t$e a,o*nt o) radioisoto#e int$e s*#ernatant wit$ a Gei%er co*nter.o,#are it wit$ t$e startin% a,o*nt.
7.
!*s#ension o)E. coli cells
32'"labeled/2 #$a%e
35!"labeled/2 #$a%e
!*#ernatantwit$35!"labelede,#t- #$a%e
'ellet wit$*nlabeledD( inin)ectedE. coli cells
!*#ernatantwit$*nlabelede,#t- #$a%e
'ellet wit$32'"labeledD( inin)ectedE. coli cells
!*s#ension o)E. coli in)ected wit$35!"labeled #$a%e
!*s#ension o)E. coli in)ected wit$32'"labeled #$a%e
35!"labeled#rotein ca#sid
acterial cell
()ter blendin%
iral %enetic,aterial
iral%enetic,ateriallabeled
acterialcell
!$eared e,#t-#$a%es labeled
!$eared e,#t-#$a%e labeled
32'"labeledD(
!$earede,#t-#$a%es*nlabeled
!$earede,#t-
#$a%e
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The Data
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80%Blending removes 80%of35S fromE. colicells.
35%Most of the32P (65%)remains with intactE. colicells.
Totalisotopei
nsupernatant(%)
Agitation time in blender (min)
100
80
60
40
20
00 1 2 3 4 5 6 7 8
Data from A. D. Hershey and Martha Chase (1952) Independent Functions of Viral Protein and Nucleic Acid in Growth ofBacteriophage.Journal of General Physiology36, 3956.
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Extracellular35S
Extracellular32P
22
I i h D
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80%Blending removes 80%of35S fromE. colicells.
35%
Most of the32
P (65%)remains with intactE. colicells.
Totaliso
topeinsupernatant(%)
Agitation time in blender (min)
100
80
60
40
20
00 1 2 3 4 5 6 7 8
Data from A. D. Hershey and Martha Chase (1952) Independent Functions of Viral Protein and Nucleic Acid in Growth ofBacteriophage.Journal of General Physiology36, 3956.
Extracellular35S
Extracellular32P
Interpretin* the Data
9-18
,ost o5 the $"S .as 5ound
in the supernatantJut onl a sall
percenta*e o5 $!3
These results su**est that DNA is inGected into the ?acterial ctoplasdurin* in5ection
Data is not conclusie since less than 100 o5 the DNA or protein
ended up in the cell or supernatant
Data is consistent .ith the hpothesis that DNA is the *enetic
aterial 23
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In 19" A2 -ierer and -2 Schra isolated RNA
5ro the to?acco osaic irus (T,H) a plant irus 3uri5ied RNA caused the sae lesions as intact T,H
iruses There5ore the iral *enoe is coposed o5 RNA
Since that tie an RNA iruses hae ?een
5ound Re5er to Ta?le 921
RNA Bunctions as the -enetic ,aterial
in Soe Hiruses
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92! NUCLEIC ACID
STRUCTURE > On Your Own7 DNA and RNA are lar*e acroolecules .ith
seeral leels o5 copleit
> 12 Nucleotides 5or the repeatin* unit o5 nucleic acids> !2 Nucleotides are lin@ed to 5or a linear strando5
RNA or DNA
> $2 T.o strands can interact to 5or a dou?le heli
> %2 The $D structure o5 DNA results 5ro 5oldin* and?endin* o5 the dou?le heli2 Interaction o5 DNA .ith
proteins produces chroosoes .ithin liin* cells
> Re5er to 5i*2 92
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!igure ".(
CC
G
AA
GA
T
GG
TT TA
A
G
C
A
T
ATT TAG
C
Nucleotides
Single strand
Double helix
Three-dimensional structure
ATCGCA A
TCATGC
AATCGCA
GCA T
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The nucleotideis the repeatin* structural unit o5DNA and RNA
It has three coponents A phosphate *roup
A pentose su*ar
A nitro*enous ?ase
Re5er to Bi*ure 92'
Nucleotides
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9-24!igure ".)
Phosphate group Sugars
D-Deoxyribose (in DNA)
Purines(double ring)
Pyrimidines(single ring)
Bases
OO
O
O
P
H
H
H
HO
OHOHOCH2
HH
D-Ribose (in RNA)
H
OH
H
HO
OHOHOCH2
HH
Uracil (U) (in RNA)Thymine (T) (in DNA)
Cytosine (C)
Adenine (A)
Guanine (G)
NH2
N
HH
H
H
H
O
N
43
2
156
7
8
9
43
21
5
6
O
CH3 H
432
156
7
8
9
5M
O
NH2
H
HN
N
N
N
NH2
N
N
H
N
N
NH
H O
N43
21
5
6
O
HH O
43
21
5
6
N
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4M 1M
2M3M
5M
4M 1M
3M 2M
N
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HH
H
OCH2
Base
(a) Repeating unit of deoxyribonucleic acid (DNA)
(b) Repeating unit of ribonucleic acid (RNA)
Phosphate
Deoxyribose
HH
OH
OCH2
Base
Phosphate
Ribose
5M
OH OH
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4M 1M
3M 2M
5M
4M 1M
3M 2M
OO
O
P
O
O
O
P
O
O
HH HH
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!igure ".* The structure of nucleotides found in (a) DN and (b) !N
" #" $ or T
These atos are 5ound .ithin indiidual nucleotides /o.eer the are reoed .hen nucleotides Goin to*ether to a@e
strands o5 DNA or RNA
" #" $ or %
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Jase su*arnucleoside Eaple
Adenine ri?ose AdenosineAdenine deori?ose Deoadenosine
Jase su*ar phosphate(s)
nucleotide Eaple
Adenosine onophosphate (A,3)
Adenosine diphosphate (AD3)
Adenosine triphosphate (AT3)
Re5er to Bi*ure 929
31
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Copyright The McGraw-Hill Companies, Inc. Permission required or reproduction or display!igure "."
&ase al'ays
attached here
hosphates are
attached here
Adenosine
Adenosine monophosphate
Adenosine diphosphate
Adenine
Phosphate groups
Phosphoester bond
Ribose
H
OP CH2
O
OO P
O
O O O
O P
O
H
OHHO
O
H2M3
1M4M5M
Adenosine triphosphate
NH2
N
H
H
N
NN
32
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Nucleotides are coalentl lin@ed to*ether ?
phosphodiester ?onds A phosphate connects the " car?on o5 one nucleotide to
the $ car?on o5 another
There5ore the strand has directionalit " to $
In a strand all su*ar olecules are oriented in the sae
direction
The phosphates and su*ar olecules 5or the?ac@?oneo5 the nucleic acid strand The ?ases proGect 5ro the ?ac@?one
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!igure ".#+
NH2
N O
N
O
N O
N
Adenine (A)
Guanine (G)
Thymine (T)
BasesBackbone
Cytosine (C)
O
HH
H
H
HH
OOO
O
P CH2
O
HH
H
H
H
HH
OOO
O
P CH2
O
NH2
N
N
H
N
N
HH
H
HH
OOO
O
P CH2
O
NH2
HN
N
N
H
N
HH
HOH
HH
OOO
O
P CH2
OSinglenucleotide
Phosphodiesterlinkage
Sugar (deoxyribose)
Phosphate
3M
5M
5M4M 1M
2M3M
5M
4M 1M
2M3M
5M
4M 1M
2M3M
5M
4M 1M
2M3M
CH3
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In 19"$ Faes ;atson and Brancis Cric@ elucidated
the dou?le helical structure o5 DNA
The scienti5ic 5rae.or@ 5or their ?rea@throu*h .as
proided ? other scientists includin* Linus 3aulin*
Rosalind Bran@lin and ,aurice ;il@ins Er.in Char*a55
A Be. e Eents Led to the Discoer o5
the Structure o5 DNA
35
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In the earl 19"0s he
proposed that re*ions o5
protein can 5old into a
secondar structure heli
Linus 3aulin*
!igure ".##
To elucidate this structure
he ?uilt ?allandstic@odels
o#-ri%$t /$e cGraw"ill o,#anies Inc. 'er,ission re*ired )or re#rod*ction or dis#la-.
CC
C
CCC
O
C
O
OC
O
H
H
H
H
N
CN
NN
CC
CC O
O
HH
NN
C
C
C
CC
C
O
C
O
C
O
OC
O
H
HH
N
NN
H
N
H
N
Carbonyloxygen
Amidehydrogen
Hydrogenbond
(a) An helix in a protein
36
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Wet DNA fibers
X-ray beam
The pattern represents theatomic array in wet fibers.
X rays diffractedby DNA
(b) X-ray diffraction of wet DNA fibers
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She .or@ed in thesae la?orator as
,aurice ;il@ins
She used Ora
di55raction to stud
.et 5i?ers o5 DNA
Rosalind Bran@lin
The di55raction pattern is interpreted(usin* atheatical theor)
This can ultiatel proide
in5oration concernin* the
structure o5 the olecule
!igure ".#$
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Copyright The McGraw-Hill Companies, Inc. Permission required or reproduction or display
She ade ar@ed adances in Ora di55ractiontechni4ues .ith DNA
The di55raction pattern she o?tained su**estedseeral structural 5eatures o5 DNA
/elical
,ore than one strand 10 ?ase pairs per coplete turn
38
Rosalind Bran@lin
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Char*a55 pioneered an o5 the ?iocheicaltechni4ues 5or the isolation puri5ication and
easureent o5 nucleic acids 5ro liin* cells
It .as @no.n that DNA contained the 5our ?ases8
A - C and T
Char*a55 analed the ?ase coposition o5 DNA
isolated 5ro an di55erent species
Er.in Char*a55s Eperient
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The /pothesis
>An analsis o5 the ?ase coposition o5 DNA indi55erent species a reeal iportant 5eatures
a?out the structure o5 DNA
Copyright The McGraw-Hill Companies, Inc. Permission required or reproduction or display
Testin* the /pothesis
Re5er to Bi*ure 921$
40
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!igure ".#%
o#-ri%$t /$e cGraw"ill o,#anies Inc. 'er,ission re*ired )or re#rod*ction or dis#la-.
:#eri,ental level once#t*al level
;or eac$ t-#e o) cell etract t$ec$ro,oso,al ,aterial. /$is can bedone in a variet- o) wa-s incl*din% t$e*se o) $i%$ salt deter%ent or ,ild alkalitreat,ent. ote< /$e c$ro,oso,escontain bot$ D( and #rotein.
1.
=e,ove t$e #rotein. /$is can be done inseveral wa-s incl*din% trea,ent wit$#rotease.
2.
-drol->e t$e D( to release t$e bases)ro, t$e D( strands. ( co,,on wa-to do t$is is b- stron% acid t reat,ent.
3.
!e#arate t$e bases b- c$ro,ato%ra#$-.'a#er c$ro,ato%ra#$- #rovides an eas-wa- to se#arate t$e )o*r t-#es o) bases./$e tec$ni*e o) c$ro,ato%ra#$- is
described in t$e (##endi.
4.
:tract bands )ro, #a#er into sol*tionsand deter,ine t$e a,o*nts o) eac$ baseb- s#ectrosco#-. :ac$ base will absorbli%$t at a #artic*lar wavelen%t$. -ea,inin% t$e absor#tion #ro?le o) asa,#le o) base it is t$en #ossible tocalc*late t$e a,o*nt o) t$e base.!#ectrosco#- is described in t$e(##endi.
5.
o,#are t$e base content in t$e D()ro, di+erent or%anis,s.
6.
!ol*tion o)c$ro,oso,aletract
D(
D( @#roteins
Individ*albases
Ari%in
'rotease
(cid'
'
''' '
''
%%
% %% %%
GG G
G G GG
G
G
G
%
%
%
-
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The Data
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Interpretin* the Data
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The data sho.n in Bi*ure 921$ are onl a sallsaplin* o5 Char*a55s results
The copellin* o?seration .as that 3ercent o5 adenine percent o5 thine 3ercent o5 ctosine percent o5 *uanine
This o?seration ?ecae @no.n as Char*a55s rule It .as a crucial piece o5 eidence that ;atson and Cric@
used to elucidate the structure o5 DNA
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Bailiar .ith all o5 these @e o?serations ;atsonand Cric@ set out to sole the structure o5 DNA The tried to ?uild ?allandstic@ odels that incorporated
all @no.n eperiental o?serations
A critical 4uestion .as ho. the t.o (or ore strands)
.ould interact
An earl hpothesis proposed that DNA strands interactthrou*h phosphate,*crosslin@s
Re5er to Bi*ure 921%
;atson and Cric@
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Copyright The McGraw-Hill Companies, Inc. Permission required or reproduction or display
!igure ".#&
This hpothesis .as o5 course incorrectP
Copri*ht + The ,c-ra./ill Copanies Inc2 3erission re4uired 5or reproduction or displa2
!*%ar
BA
A A
A
'
ase
!*%ar
ase
!*%ar
A
AA
'
ase
!*%ar
aseAB
%2@
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Copyright The McGraw-Hill Companies, Inc. Permission required or reproduction or display
The .ent ?ac@ to the ?allandstic@ units The then ?uilt odels .ith the
Su*arphosphate ?ac@?one on the outside
Jases proGectin* to.ard each other
The 5irst considered a structure in .hich ?ases 5or
/ ?onds .ith identical ?ases in the opposite strand ie2 A to A T to T C to C and - to -
,odel ?uildin* reealed that this also .as incorrect
;atson and Cric@
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Copyright The McGraw-Hill Companies, Inc. Permission required or reproduction or display
The then realied that the hdro*en ?ondin* o5 A toT .as structurall siilar to that o5 C to - So the ?uilt ?allandstic@ odels .ith AT and C-
interactions ?et.een the t.o DNA strands These .ere consistent .ith all @no.n data a?out DNA structure
Re5er to Bi*ure 921"
;atson Cric@ and ,aurice ;il@ins .ere a.ardedthe No?el 3rie in 19! Rosalind Bran@lin died in 19"& and No?el pries are not
a.arded posthuousl
;atson and Cric@
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(b) Original model of the DNA double helix
(a) Watson and Crick
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arrin%ton rownC'$oto =esearc$ers
*lton(rc$ive b- Gett- I,a%es
!igure ".#' 48
The DNA Dou?le /eli
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-eneral structural 5eatures (Bi*ures 921 Q 921')
The DNA Dou?le /eli
> 6n our 6.n
T.o strands are t.isted to*ether around a
coon ais
There are 10 ?asesand $2% n per coplete turno5 the heli
The t.o strands are antiparallel
6ne runs in the " to $ direction and the other $ to " The heli is ri*hthanded
As it spirals a.a 5ro ou the heli turns in a
[email protected] direction
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-eneral structural 5eatures (Bi*ures 921 Q 921')
The DNA Dou?le /eli
The dou?le?onded structure is sta?ilied ?
12 /dro*en ?ondin* ?et.een copleentar ?ases A ?onded to T ? t.o hdro*en ?onds
C ?onded to - ? three hdro*en ?onds
!2 Jase stac@in* ;ithin the DNA the ?ases are oriented so that the 5lattened
re*ions are 5acin* each other
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Copyright The McGraw-Hill Companies, Inc. Permission required or reproduction or display!igure ".#(
Copri*ht + The ,c-ra./ill Copanies Inc2 3erission re4uired 5or reproduction or displa2
H
N HN
N
N
G
NH2
H
P
S
P
SP
5end
3end
H NH2
N
N
HH
H
HH
OOO
O
P CH2
O
HH
H
OH
HH
OOO
O
P CH2
O
HH
H
HH
OOO
O
P CH2
O
CH2
HH
H
HH
OOO
O
P
O
T
ey Feat"re*
Two strands of DNA form aright-handed double helix.
The bases in opposite strandshydrogen bond according to the
AT/GC rule.
The 2 strands are antiparallel withregard to their 5 to 3 directionality.M M
There are ~10.0 nucleotides in eachstrand per complete 360 turn ofthe helix.
2 nm
One nucleotide0.34 nm
One completeturn 3.4 nm
TA
G C
T AP
P
P
P
P
S
S
S
S
S
S
S
S
S
A
C
G
C G
C G
G C
G C
GC
G C
C
P
P
S
P
PP
P
P
S
SS
S
S
P
P
P
P
P
P
P
P
P
P
S
S S
S
S
S
S
S
SP
S
S
P
P
P
S
S
S
SP
3
5
G
S
35
S
A
P
P
C
T A
O
N
N
N
NA
H
H NH2
N
O
H
N
CH3
H
T
H
HH2N
N
N C
O
3end
5end
H
H
HH
OOO
O
PCH2
O
H
H
H
H
HH
OOO
O
PCH2
O
H
H
HH
OOO
O
PCH2
O
H
H
HH
OOO
O
PCH2
O
HO
N
O
H
N
CH3
H
T
O
NH N
N
N
G
H2N
H
H
H
N
N
N
N A
H
H2N H
"
"
"
"
"
"
"
"
""
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-eneral structural 5eatures (Bi*ures 921 Q 921')
The DNA Dou?le /eli
There are t.o asetrical *rooeson the
outside o5 the heli 12 ,aGor *rooe
!2 ,inor *rooe
Certain proteins can ?ind .ithin these *rooes The can thus interact .ith a particular se4uence o5 ?ases
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(b) Space-filling model of DNA(a) Ball-and-stick model of DNA
Minorgroove
Majorgroove
Minorgroove
Majorgroove
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Ea%*na Desi%nC'$oto =esearc$ers
!igure ".#) 53
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54
/o calc*late $ow o)ten t$e en>-,e willc*t
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