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PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Chapter 16
he !olecular Basis o"
Inheritance
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Overview: Lifes Operating Instructions
In 1953, James Watson an !rancis "ric#
s$oo# t$e wor%
# Wit$ an e%egant ou&%e'$e%ica% moe% for t$e
structure of eo()ri&onuc%eic aci, or *+
Figure 16.1
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*+, t$e su&stance of in$eritance
# Is t$e most ce%e&rate mo%ecu%e of our time
-ereitar) information
# Is encoe in t$e c$emica% %anguage of *+an reprouce in a%% t$e ce%%s of )our &o)
It is t$e *+ program
# .$at irects t$e eve%opment of man) ifferent
t)pes of traits
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"oncept 1/01: *+ is t$e genetic materia%
ar%) in t$e 2t$ centur)
# .$e ientification of t$e mo%ecu%es of
in$eritance %oome as a ma4or c$a%%enge to
&io%ogists
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The Search for the Genetic Material:Scientific Inquiry
.$e ro%e of *+ in $ereit)
# Was first wor#e out &) stu)ing &acteria ant$e viruses t$at infect t$em
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Evidence That DNA Can Transform acteria
!reeric# riffit$ was stu)ing Streptococcus
pneumoniae# &acterium t$at causes pneumonia in
mamma%s
-e wor#e wit$ two strains of t$e &acterium
# pat$ogenic strain an a nonpat$ogenic
strain
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riffit$ foun t$at w$en $e mi(e $eat'#i%%e
remains of t$e pat$ogenic strain# Wit$ %iving ce%%s of t$e nonpat$ogenic strain,
some of t$ese %iving ce%%s &ecame pat$ogenic 6acteria of t$e 78 smoot$; strain of Streptococcus pneumoniaeare pat$ogenic &ecause t$e)
$ave a capsu%e t$at protects t$em from an anima%s efense s)stem0 6acteria of t$e 7
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riffit$ ca%%e t$e p$enomenon transformation
# +ow efine as a c$ange in genot)pe anp$enot)pe ue to t$e assimi%ation of e(terna%
*+ &) a ce%%
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Evidence That !iral DNA Can "ro#ram Cells
itiona% evience for *+ as t$e genetic
materia%# "ame from stuies of a virus t$at infects
&acteria
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>iruses t$at infect &acteria, &acteriop$ages
# re wie%) use as too%s &) researc$ers inmo%ecu%ar genetics
Figure 16."
Phage
head
Tail
Tail #i$er
%N&
'a(terial
(ell
133nm
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%fre -ers$e) an =art$a "$ase
# Performe e(periments s$owing t$at *+ ist$e genetic materia% of a p$age #nown as .2
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.$e -ers$e) an "$ase e(periment In t$eir famous 1952 e(periment, %fre -ers$e) an =art$a "$ase use raioactive su%fur
an p$osp$orus to trace t$e fates of t$e protein an *+, respective%), of .2 p$ages t$at infecte &acteria% ce%%s0
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rwin "$argaff ana%)Be t$e &ase composition of *+
# !rom a num&er of ifferent organisms
In 19AC, "$argaff reporte
# .$at *+ composition varies from one species to
t$e ne(t
.$is evience of mo%ecu%ar iversit) among species
# =ae *+ a more crei&%e caniate for t$e genetic
materia%
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Building a Structural Model of DNA:Scientific Inquiry
Once most &io%ogists were convince t$at *+
was t$e genetic materia%# .$e c$a%%enge was to etermine $ow t$e
structure of *+ cou% account for its ro%e in
in$eritance
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=aurice Wi%#ins an
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Figure 16.3a2 (
"
.
.
"
"
"
.
.
.
.
"
.
03A nm
30A nm
/a0 4e #eatures o# %N& stru(ture
1 nm
/(0 Spa(e+#illi-g 5odel
.
Watson an "ric# euce t$at *+ was a
ou&%e $e%i(# .$roug$ o&servations of t$e D'ra)
cr)sta%%ograp$ic images of *+
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!ran#%in $a conc%ue t$at *+
# Was compose of two antipara%%e% sugar'p$osp$ate &ac#&ones, wit$ t$e nitrogenous
&ases paire in t$e mo%ecu%es interior
.$e nitrogenous &ases
# re paire in specific com&inations: aenine
wit$ t$)mine, an c)tosine wit$ guanine
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O
@O O
O-
O
@OO
O
-2"
O
@OO
O
-2"
O
@OO
O
O-
O
O
O.
"
"
.
O
O
O
"-2
OO@
OO
"-2
"-2
"-2
5en
-)rogen &on
3en
3en
P
P
P
P
O
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O@
O
O
O
P
P
O@
OO
O
P
O@
OO
O
P
/$0 Partial (he5i(al stru(ture
-2"
5enFigure 16.3$
O
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Watson an "ric# reasone t$at t$ere must &e
aitiona% specificit) of pairing# *ictate &) t$e structure of t$e &ases
ac$ &ase pair forms a ifferent num&er of
$)rogen &ons
# enine an t$)mine form two &ons,
c)tosine an guanine form t$ree &ons
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+ - O "-3
+
+
O
+
+
+
+ -
8ugar
8ugar
&de-i-e /&0 Th5i-e /T0
+
+
+
+
8ugar
O - +
-
+-
+ O-
-
+
8ugar
ua-i-e /0 Ctosi-e /C0Figure 16.7
-
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"oncept 1/02: =an) proteins wor# toget$er in
*+ rep%ication an repair .$e re%ations$ip &etween structure an
function
# Is manifest in t$e ou&%e $e%i(
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The Basic rinci!le: Base airing to a Tem!late Strand
8ince t$e two strans of *+ are
comp%ementar)# ac$ stran acts as a temp%ate for &ui%ing a
new stran in rep%ication
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In *+ rep%ication
# .$e parent mo%ecu%e unwins, an two newaug$ter strans are &ui%t &ase on &ase'
pairing ru%es
/a0.$e parent mo%ecu%e $as two
comp%ementar) strans of *+0
ac$ &ase is paire &) $)rogen
&oning wit$ its specific partner,
wit$ . an wit$ "0
/$0.$e first step in rep%ication is
separation of t$e two *+
strans0
/(0 ac$ parenta% stran now
serves as a temp%ate t$at
etermines t$e orer of
nuc%eoties a%ong a new,
comp%ementar) stran0
/d0 .$e nuc%eoties are connecte
to form t$e sugar'p$osp$ate
&ac#&ones of t$e new strans0
ac$ 7aug$ter *+
mo%ecu%e consists of one parenta%
stran an one new stran0
&
C
T
&
&
C
T
&
&
C
T
&
&
C
T
&
T
&
T
C
T
&
T
C
&
C
T
&
&
C
T
&
T
&
T
C
T
&
T
C
T
&
T
C
T
&
T
C
Figure 16.8 a9d
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Copyright 2005 Pearson Education, Inc. publishing as Benjamin CummingsFigure 16.1: a9(
Co-ser;ati;e
5odel..$e two
parenta% stransreassociate
after acting astemp%ates fornew strans,
t$us restoring
t$e parenta%ou&%e $e%i(0
Se5i(o-ser;ati;e
5odel. .$e twostrans of t$eparenta% mo%ecu%e
separate,an eac$ functions
as a temp%ate
for s)nt$esis ofa new, comp%e'
mentar) stran0
%ispersi;e
5odel.ac$
stran of both
aug$ter mo%'
ecu%es containsa mi(ture of
o% an new%)
s)nt$esiBe*+0
Pare-t (ell
First
repli(atio-Se(o-drepli(atio-
*+ rep%ication is semiconservative
# ac$ of t$e two new aug$ter mo%ecu%es wi%%$ave one o% stran, erive from t$e parent
mo%ecu%e, an one new%) mae stran/a0
/$0
/(0
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(periments performe &) =ese%son an 8ta$%
# 8upporte t$e semiconservative moe% of *+rep%ication
Figure 16.11
=att$ew =ese%son an !ran#%in 8ta$% cu%ture E. coli&acteria for severa% generations
on a meium containing nuc%eotie precursors %a&e%e wit$ a $eav) isotope of nitrogen, 15+0 .$e &acteria
incorporate t$e $eav) nitrogen into t$eir *+0 .$e scientists t$en transferre t$e &acteria to a meium wit$
on%) 1A+, t$e %ig$ter, more common isotope of nitrogen0 n) new *+ t$at t$e &acteria s)nt$esiBe wou% &e
%ig$ter t$an t$e parenta% *+ mae in t$e 15+ meium0 =ese%son an 8ta$% cou% istinguis$ *+ of ifferentensities &) centrifuging *+ e(tracte from t$e &acteria0
EXPERIMENT
.$e &ans in t$ese two centrifuge tu&es represent t$e resu%ts of centrifuging two *+ samp%es from t$e f%as#
in step 2, one samp%e ta#en after 2 minutes an one after A minutes0
RESULTS
6acteria
cu%ture in
meium
containing15+
6acteria
transferre to
meium
containing1A+
!1
*+ samp%e
centrifuge
after 2 min
after first
rep%ication;
" *+ samp%e
centrifuge
after A min
after secon
rep%ication;
*
Less
ense
=ore
ense
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CONCLUSION =ese%son an 8ta$% conc%ue t$at *+ rep%ication fo%%ows t$e semiconservative
moe% &) comparing t$eir resu%t to t$e resu%ts preicte &) eac$ of t$e t$ree moe%s in !igure 1/010
.$e first rep%ication in t$e 1A+ meium prouce a &an of $)&ri 15+@1A+; *+0 .$is resu%t e%iminate
t$e conservative moe%0 secon rep%ication prouce &ot$ %ig$t an $)&ri *+, a resu%t t$at e%iminatet$e ispersive moe% an supporte t$e semiconservative moe%0
First repli(atio- Se(o-d repli(atio-
Co-ser;ati;e
5odel
Se5i(o-ser;ati;e
5odel
%ispersi;e
5odel
DNA R li i A Cl & '
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DNA Re!lication:A Closer &oo'
.$e cop)ing of *+
# Is remar#a&%e in its spee an accurac)
=ore t$an a oBen enB)mes an ot$er proteins
# Participate in *+ rep%ication
$ i S d ) i i f R li i
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$ettin# Started( )ri#ins of Replication
.$e rep%ication of a *+ mo%ecu%e
# 6egins at specia% sites ca%%e origins ofrep%ication, w$ere t$e two strans are
separate
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eu#ar)otic c$romosome
# =a) $ave $unres or even t$ousans ofrep%ication origins
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A ti ll l El ti
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Antiparallel Elon#ation
-ow oes t$e antipara%%e% structure of t$e
ou&%e $e%i( affect rep%icationF
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*+ po%)merases a nuc%eoties
# On%) to t$e free 3 en of a growing stran
%ong one temp%ate stran of *+, t$e %eaing
stran
# *+ po%)merase III can s)nt$esiBe a
comp%ementar) stran continuous%), moving
towar t$e rep%ication for#
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.o e%ongate t$e ot$er new stran of *+, t$e
%agging stran
# *+ po%)merase III must wor# in t$e irection
awa) from t$e rep%ication for#
.$e %agging stran
# Is s)nt$esiBe as a series of segments ca%%e
O#aBa#i fragments, w$ic$ are t$en 4oine
toget$er &) *+ %igase
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Pare-tal %N&
*+ po% I%% e%ongates
*+ strans on%) in t$e
5 3irection0
1
O#aBa#i
fragments
*+ po% III
.emp%ate
stran
Lagging stran3
2
.emp%ate
stran *+ %igase
Overa%% irection of rep%ication
One new stran, t$e %eaing stran,
can e%ongate continuous%) 5 3
as t$e rep%ication for# progresses0
!
.$e ot$er new stran, t$e
%agging stran must grow in an overa%%
3 5irection &) aition of s$ort
segments, O#aBa#i fragments, t$at grow
5 3num&ere $ere in t$e orer
t$e) were mae;0
"
*+ %igase 4oins O#aBa#ifragments &) forming a &on &etween
t$eir free ens0 .$is resu%ts in a
continuous stran0
*
Figure 16.1*
35
5
3
3
5
21
Leaing stran
1
8)nt$esis of %eaing an %agging strans uring
*+ rep%ication
"rimin# DNA Synthesis
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"rimin# DNA Synthesis
*+ po%)merases cannot initiate t$e s)nt$esis
of a po%)nuc%eotie
# .$e) can on%) a nuc%eoties to t$e 3en
.$e initia% nuc%eotie stran
# Is an
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Overa%% irection of rep%ication
3
3
3
3
5
35
35
3
5
3
5
3
5
3
5
3 5
5
1
1
21
12
5
5
12
35
.emp%ate
stran
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)ther "roteins That Assist DNA Replication
-e%icase, topoisomerase, sing%e'stran &ining
protein
# re a%% proteins t$at assist *+ rep%ication
Ta$le 16.1
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Copyright 2005 Pearson Education, Inc. publishing as Benjamin CummingsFigure 16.16
Overa%% irection of rep%icationLeaing
stran
Lagging
stran
Lagging
stran
Leaing
stranO>IW
Leaing
stran
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The DNA Replication %achine as a Stationary Comple+
.$e various proteins t$at participate in *+
rep%ication
# !orm a sing%e %arge comp%e(, a *+
rep%ication 7mac$ine
.$e *+ rep%ication mac$ine
# Is pro&a&%) stationar) uring t$e rep%ication
process
roofreading and Re!airing DNA
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roofreading and Re!airing DNA
*+ po%)merases proofrea new%) mae *+
#
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Figure 16.13
+uc%ease
*+
po%)merase
*+
%igase
t$)mine imer
istorts t$e *+ mo%ecu%e0
1
nuc%ease enB)me cuts
t$e amage *+ stran
at two points an t$eamage section is
remove0
!
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Re!licating the "nds of DNA Molecules
.$e ens of eu#ar)otic c$romosoma% *+
# et s$orter wit$ eac$ roun of rep%ication
Figure 16.17
n of parenta%
*+ strans
Leaing stran
Lagging stran
Last fragment Previous fragment
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u#ar)otic c$romosoma% *+ mo%ecu%es
# -ave at t$eir ens nuc%eotie se?uences,ca%%e te%omeres, t$at postpone t$e erosion of
genes near t$e ens of *+ mo%ecu%es
Figure 16.18 1 Em
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If t$e c$romosomes of germ ce%%s &ecame
s$orter in ever) ce%% c)c%e
# ssentia% genes wou% eventua%%) &e missing
from t$e gametes t$e) prouce
n enB)me ca%%e te%omerase
# "ata%)Bes t$e %engt$ening of te%omeres in
germ ce%%s