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The Nucleus
The nucleus is the headquarters of theThe nucleus is the headquarters of thecell. Itcell. It is the most obvious organelle in
any eukaryotic cell and appears as aa
large dark spot in EUKA!"TI# cells. Itlarge dark spot in EUKA!"TI# cells. Itcontrols all cell activity.controls all cell activity.
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• The Nucleus is a membrane$enclosed organelle %hich house
most of the genetic information
and regulatory machineryresponsible for providing the cell
%ith its unique characteristics.
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Nucleus is the most important organelle in cell.
In mammalian cells& e'cepting (#&
all cells else are the nucleus contained cells.
In prokaryotic cells& there is no membraneto package the nucleic acid substance& so&
%e call this nucleic substance enriched
area as )Nucleoid*.
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The ma+or structures of nucleus include,
① nuclear envelope.
② nucleolus.
③ nuclear matri'.
④ chromatin.
⑤ nuclear lamina.
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The ma+or functions of nucleus,
① inheritance, maintain the geneticcontinuity of generation by the
replication of -NA chromatin and the
proliferation of cell.② development, regulate the cell
differentiation by the regulation of
spatiotemporal sequence of genee'pression.
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• TE NU#/EU0,• 1UN#TI"N0
• It stores the cell2s hereditary material& or -NA.
• 0ite of -NA replication
• 0ite of -NA transcription to mNA
• ibosomal formation
– Nucleolus, NA 3 protein required for ribosomal
synthesis
• It coordinates the cell2s activities& %hich include
gro%th& intermediary metabolism& protein synthesis&and reproduction 4cell division5 by regulating gene
e'pression.
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http://upload.wikimedia.org/wikipedia/commons/3/38/Diagram_human_cell_nucleus.svg
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nuclearpores
chromatin
nucleolus
nuclearenvelope
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nuclearpores
nucleus
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I. Nuclear envelope 4Nuclear membrane5
Nuclear envelope is the lipid bilayer that packages
the nucleus.
Nuclear envelope separates the -NA from cell plasma
and forms a stable inner environment to,
① protect the -NA from damage&
② separate the replication of -NA from the
translation of NA spatiotemporally&
③ the chromatin is anchored on to the nuclear
envelope& that is beneficial to be despiraled&
replicated& condensed& and distributed into ne%nuclei equally&
④ the pores on the envelope are the channels for
the substance e'change.
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Nuclear envelope is bilayer membrane,
Nuclear envelope is composed of
inner nuclear membrane&
outer nuclear membrane& andperinuclear space.
There are nuclear pores on the membrane
that are linked %ith plasma.
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• The inner surface of the NE is bound to
a thin filamentous net%ork 4lamins
polypeptides5 called the nuclearlamina. It provides mechanical support
to the NE and seeves as sites for
attachment for chromatin fibers.
• 9utations in the lamin genes are
responsible for several distinct human
diseases 4e.g. a rare form of muscular
dystrophy5.
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The nuclear pores are the channels for the
substance transportation,
•Nuclear proteins are synthesi:ed in plasma& then
%ill be imported into nucleus by the pores.
•The NAs and the ribosome subunits synthesi:ed
in nucleus %ill be e'ported into plasma by the
pores also.
•In addition& it is indicated by a in+ection
e'periment that small molecules can enter the
nucleus by diffusion from the pores.
TE NU#/EA ;"E
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Nuclear pores are composed of 87 different
nucleoporins at least& and %e call these pore
structure as nuclear pore comple' 4N;#5.
Usually& a mammalian nucleus contains
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The structures of nuclear pore include
① cytoplasmic ring located on the cell
plasma part of the pore comple'contains filaments e'tending into
plasma.
② nuclear ring located on the nuclear
plasma part of the pore comple'
e'tending filaments also.
③ transporter located in center of the
pore as a plug particle.④ 0poke located on the edge of the pore
as the spines.
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•
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The nuclear pore structures on the cell plasma side after an e'traction
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The nuclear pore structures on the nuclear plasma side after an e'traction
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Nuclear plasma protein 4nucleoplasmin5 is
transported by the follo%ing steps,
① The protein combines to the B C D dimer ofthe receptor 4imporin5.
② The comple' of the protein transported
and the receptor used combines to thefilaments located on the N;# cytoplasmic
ring.
③ The filaments curve to the nuclear center&
the transporter structure %ill be changedto form a hydrophilic channel& and the
protein passes through the channel.
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④ The comple' of the protein transported
and the receptor used combines to an$
T;& the comple' is disassembled andreleases out the protein transported.
⑤ The imporin D combined %ith an$T; %ill
be e'ported out of the nucleus& the T;
combined %ith an %ill be hydroly:ed incell plasma& and the an$-; %ill go back
to nucleus to be transformed to an$T;
again.
⑥ The imporin B %ill be transported back to
cell plasma %ith the help from e'portin.
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Fe kno% a little about ho% the macromolecules are
transported to cell plasma from nucleus.
In most of cases& the NA in nucleus iscombined %ith protein to form an N; comple'&
then& transported into cell plasma.
There is nuclear e'portation signal 4NE05 on the
protein of N; comple' that can combine to the
intracellular receptor& e'portin& to form the
comple' of N;$e'portin$an$T;.
In the cell plasma& this comple' %ill bedisassembled and release out the an$T;& NA&
an$-;& e'portin& and N; protein.
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The nucleoplasmin is transported into nucleus
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#hromosome
#hromatin %as named byF. 1lemming in 6=G.
#hromosome %as named by
Faldeyer in 6.
#hromatin and chromosome are
same substance %ith different shape
presentation in different cell cyclephases.
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The chemical components of chromatin,
-NA&
histone protein&
nonhistone protein& andsome NA
at ratio about 6,6,46$6.85,7.78.
-NA,
-NA is the carrier of genetic information.
-NA sequences can be sorted as < types,
nonrepeated fraction&
moderately repeated fraction 4676$6785& and
highly repeated fraction 4H6785.
-NA forms,
($-NA&
$-NA& and
A$-NA.
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-NA forms 4ed color sho%s the couple backbones5
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#hromosome -NA contains three basic sequences,
① autonomously replicating -NA sequence 4A05.
A0 is the starting site of -NA replication.In yeast genome& there are J77$77 A0s
included& and most of them contain a AT
enriched 66bp sequence called as A0
consensus sequence 4A#05.
② centromere -NA sequence 4#EN5 composed of
a lot of repeated sequences.
③ telomere -NA sequence 4TE/5.
TE/ is similar in different bio organisms&
and composed of 8 L 67bp repeated
sequences. uman
TE/ repeated sequence is TTA.
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In 6G
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Three basic sequences of chromosome
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I0T"NE
istone is positively charged and contains
arginine and lycine.istone is alkaline protein.
istones can be sorted as t%o types,
6. ighly conserved core histone including JA&
J(&
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The reasons for that may be as the follo%s,
6. 9ost of the amino acids of core histone
interact %ith -NA or other histones& so&any change of them %ill cause the fatal
mutation.
J. In all bio organisms& the -NA
phosphodiester skeleton that interacts%ith histone is same.
6 is easy to be mutated&
and it is species specific and tissue
specific.
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N"NI0T"NE ;"TEIN,
Nonhistone protein is
the protein that binds to the specific -NA sequence
of chromosome& so& %e call it as sequence specific
-NA binding protein.
The features of nonhistone protein are as the follo%s,
① Nonhistone protein is negatively charged andacidic protein that contains a large number of
aspartic acids and glutamic acids.
② Nonhistone protein can be synthesi:ed during
the %hole cell cycle& but histone protein issynthesi:ed during the 0 phase only.
③ Nonhistone protein can recogni:e the specific
-NA sequence.
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The functions of nonhistone are as the
follo%s,① elp -NA molecules to be pleated
and form different structure
domains that are beneficial to-NA replication and gene
transcription.
②elp to start -NA replicationreaction.
③ egulate transcription and gene
e'pression.
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1"9 -NA T" #"9"0"9E,
There are J< pairs of chromosomes in a human
nucleus.• If you open and e'tend the -NA molecule in
each chromosome& it %ill be 8 cm long.• If you link all -NA molecules in a nucleus
together& it %ill be 6.= L J.7 m long.(ut& the diameter of nucleus is shorter
than 67Mm.
The primary structure formed by the po%erfulcompaction is called as nucleosome.
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Nucleosome,
. Kornberg figured out the model of nucleosome.
Nucleosome is a beaded structure composed of core
particles and linker -NA.
Fe can describe the structure as the follo%s,
① Each nucleosome includes about J77bp -NA& one
histone core& and an 6.② The octameric histone core is composed of
molecules from JA& J(&
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410tructures of nucleosome
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#hromatin -NA filament,
The -NA is compacted to be shortened by =
folds and forms the -NA filament in 66nmdiameter %hen it %as transformed to the beaded
nucleosome chain.
#hromatin -NA e'ists in another style by that the
beaded nucleosome chain is condensed by ?
folds.
Under electron microscope& %e can see the
chromatin -NA filament in
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The -NA filaments in
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For the advanced package of the chromosome, e keep deta!" #nknonso far$ %ro&a&"', !t !s the ser!a" over"apped or p"eated "!ke the fo""os(
From )*+ to hromosome(
)*+ 11nm f!"ament -&eaded n#c"eosome cha!n. 30nm f!"ament
p"eat as "oop cha!n &!nd to the s!tes on n#c"ear ske"eton here !s +/
enr!ched assem&"' of chromosome
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Assembly of chromosome
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eterochromatin and euchromatin,
n the !nter phase -1 and 2. of ce"" c'c"e, the chromat!n !n the n#c"e#s
can &e sorted as heterochromat!n and e#chromat!n$
#chromat!n !s the )*+ reg!ons here the transcr!pt!on !s ver' act!ve$
#chromat!n "ooks "!ke "oose "oop and &r!ght sta!n!ng #nder e"ectron
m!croscope$ #chromat!n !s eas' to &e c"eaved &' n#c"ease at some
h'persens!t!ve s!tes$
eterochromat!n !s condensed !n phase !tho#t an' transcr!pt!on, so, !t
as named as !nact!ve chromat!n$ eterochromat!n !s the genet!c "a' reg!ons,
and rep"!cated "ate"', condensed ear"', that !s ca""ed as heteropyknosis$
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eterochromatin
4dark staining5
and euchromatin
4bright staining5
eterochromatin
Euchromatin
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#onstitutive
hetero$
chromatin !s
hetero
p'knosedchromat!n !n
each t'pe of
ce"" and
"ocated !n
centromere
reg!on$
/he F!g shos
'o# the
onst!t#t!ve
hetero
chromat!nd!sp"a'ed &'
f"#orescence
h'&r!d!at!on !n
s!t#$
1acultative heterochromatin
! h t h t! d
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!s heterochromat!n appeared
!n some spec!a" ce"" t'pe or
deve"op!ng stage$ /he
chromosome of fema"e
mamma"!ans !s the fac#"tat!ve
heterochromat!n$ s#a""',
fema"e mamma"!an ce""
conta!ns do#&"e
chromosomes, and one of
them !s heterochromat!n
ca""ed &arr &od'$ hen ah#man em&r'o !s deve"oped
after 16 da's, one
chromosome !"" &e
transformed as &arr &od' !th
dark sta!n!ng$ o, e can
!dent!f' the se: of a h#manem&r'o &' check!ng the &arr
&od' of the em&r'o ce""s !n the
amn!ot!c f"#!d$
The barr body like a drumstick in a %hite cell
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The structure of chromosome,
n the ; phase of ce"" c'c"e, chromat!n !"" &e transformed as chromosomes
&' the poerf#" condensat!on$ hromosomes are st!ck shape !th d!fferent "ength$
/he metaphase chromosome !s the &est stage to o&serve and n#m&er them&eca#se the morpho"og' of chromosome !s sta&"e at th!s t!me$
/he n#m&er of chromosome !s same !n the same t'pe of ce""s from d!fferent
!nd!v!d#a"s of one spec!es$ /he chromosomes of se: ce""s are hap"o!d, e mark !t
as n$ /he chromosomes of other ce""s are d!p"o!d, e mark !t as 2n$ /he
chromosomes of some ce""s of some spec!es are po"'p"o!d, s#ch as, 4n, 6n, and8n$
/he d!fferent ce""s from same !nd!v!d#a" can &e d!fferent chromosome t'pes$
For e:amp"e, &od' ce""s of rat are 2n, t !ts "!ver ce""s can &e 4n, 8n, and 16n$ /he
chromosome n#m&er of h#man endometr!a" ce"" !s var!a&"e from 2n
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The terms used to the structure of chromosome,
6. #hromatid, ;etaphase chromosome !s composed of to chromat!ds !th a
=#nct!on at the centromere s!te$ ach chromat!d !s formed &' the over"apped and
p"eated )*+ do#&"e strands$ hen the ce"" !s d!v!d!ng the chromat!ds can &e
separated !nto to ne ce""s$J. #hromonema, n the or phase ce""s, each chromonema !nd!cates a
chromat!d$
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The terms of chromosome structure
? N l l i i i 4N" 5 /h th h th
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?. Nucleolar organi:ing regions 4N"s5, /he' are the areas here the genes
for r!&osome >*+ are "ocated$ /he' can s'nthes!e the 28, 18, and 5$8 r>*+
for r!&osome$ *?>s can e:!st !n secondar' constr!ct!on$
=.
0atellite, t !s a &a"" part "ocated at the term!na" of chromosome, and "!nked tothe ma!n part of chromosome &' secondar' constr!ct!on$ /he sate""!te "ocated at
term!na" of chromosome !s ca""ed as term!na" sate""!te, and "ocated &eteen to
secondar' constr!ct!ons !s ca""ed as !ntermed!ate sate""!te$
. Telomere, t !s the spec!a"!ed part "ocated at the term!na" of chromosome$
/he f#nct!on of te"omere !s ma!ntenance of the sta&!"!t' of chromosome$ /e"omere!s composed of the h!gh"' repeated fract!ons, and !t !s so conserved that !t !s
s!m!"ar &eteen the tota""' d!fferent "!fe &e!ngs$ The component of human
telomere is TTA$ /e"omere !s assoc!ated !th ag!ng$ +fter each rep"!cat!on of
te"omere )*+, the te"omere !"" &e shortened &' 50 – 100&p$ /he rep"!cat!on of
te"omere !s droved &' te"omerase that has reverse transcr!ptase act!v!t'$ /h!s
en'me "acks !n norma" ce""s, so, te"omere !"" &ecome short !th the ce""pro"!ferat!on$ o, ce"" !"" &e ag!ng d#r!ng th!s act!on$
III N l l
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III. Nucleolus
*#c"eo"#s ma' &e v!s!&"e !n phase n#c"e#s$ /he' are spher!ca" and 1 – 2 for
each ce"" #s#a""'$ /he n#m&er and s!e of n#c"eo"#s are depended on the ce"" t'pe
and f#nct!on$ /he more prote!ns s'nthes!s and the faster pro"!ferat!on the ce""
takes, the more and &!gger n#c"eo"! the ce"" has$ *#c"eo"#s d!sappears &efore the
ce"" d!v!s!on, and appears !n the end of d!v!s!on$ /he ma=or f#nct!ons of n#c"eo"#s
are r>*+ transcr!pt!on and r!&osome assem&"'$
0tructure of nucleolus,
*o an' mem&rane packages n#c"eo"#s area$ /here are three spec!a" areas
can &e !dent!f!ed #nder e"ectron m!croscope( f!&r!""ar centers -F. that are①s#rro#nded &' dense f!&ers, and "o e"ectr!c dens!t'$ F conta!ns >*+ po"'merase
and r)*+ that !s naked mo"ec#"e$ dense f!&r!""ar component -)F. that !s a "oop②
or ha"f "oop to s#rro#nd F$ /ranscr!pt!on !s carr!ed o#t !n the &order reg!on of F
and )F$ gran#"ar component -. composed of 1520nm part!c"es that are③
the >*%s !n d!fferent man#fact#red steps$ >*% means the >*+ com&!ned !th
prote!n$*#c"eo"#s chromat!ns can &e sorted as to t'pes( heterochromat!n and
e#chromat!n$ /he n#c"eo"#s heterochromat!n !s a"a's "ocated aro#nd the
n#c"eo"#s, so e ca"" them as n#c"eo"#s per!phera" chromat!n$ /he n#c"eo"#s
e#chromat!n !s "ocated !n n#c"eo"#s, and n#c"eo"#s organ!!ng reg!on !n that the
r)*+ !s "ocated$
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0tructure of nucleolus
I ib
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I. ibosome
>!&osome !s the man#fact#r!ng shop to s'nthes!e prote!ns$ /here are a&o#t
20,000 r!&osomes !n an act!ve"' gro!ng &acter!#m$ >!&osome prote!ns are 10@ of
tota" prote!ns of ce"", and !ts >*+ !s 80@ of ce"" tota" >*+$
0tructure of ribosome,
/he rat!os of prote!n and >*+ to r!&osome components are 40@ and 60@$
/he r!&osome s#n!ts are composed of the com&!nat!on of the prote!n and >*+$
/he cata"'t!c act!v!t!es needed &' the trans"at!on are presented &' r!&osome
prote!n, r>*+ and other he"per factors$
/he r!&osomes can &e sorted as to t'pes$ 70 r!&osome e:!sts !n &acter!a,m!tochondr!on, and ch"orop"ast$ 80 r!&osome e:!sts !n the p"asma of e#kar'ot!c
ce""s$
>!&osome !s composed of a "arge s#n!t and a sma"" s#n!t$ /he &oth
s#n!ts !"" &e com&!ned together hen the r!&osome s'nthes!es prote!n !th
m>*+ as temp"ate$ +fter the trans"at!on, the r!&osome !"" &e separated as to
parts aga!n$ hen a prote!n !s trans"ated on an m>*+, man' r!&osomes can &!ndto the m>*+ to s'nthes!e the prote!n$ e ca"" these r!&osomes for one prote!n
s'nthes!s as polyribosome$ /he "onger m>*+ !s #sed, the more r!&osomes are
com&!ned$ /he po"'r!&osome enhances the eff!c!enc' of prote!n s'nthes!s$
%rokar'ot!c 5 r>*+ and e#kar'ot!c 5$8 r>*+ are ver' conserved for the!r
str#ct#res, so, the' can &e #sed to research the &!oevo"#t!on$
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Assembly of ribosome,
/he )*+ fragment encod!ng r>*+ !s ca""ed as r>*+ gene$ /here are a&o#t
200 cop!es of th!s gene !n a h#man ce""$ r)*+ conta!ns no h!stone core, so, !t !s a
naked )*+$/o transcr!pt r>*+, the >*+ po"'merase moves ahead a"ong the )*+
mo"ec#"e$ /he s'nthes!ed r>*+ mo"ec#"es e:tend o#t the!r mo"ec#"es from the
comp"e: of po"'merase and )*+, and form a feather"!ke str#ct#re #nder
m!croscope$
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r>*+ transcr!pt!on
/he f!"aments are the
ne s'nthes!ed 45
r>*+ that com&!nes to
prote!n to form >*%
comp"e:$ /hemeth'"ated 45 r>*+
can &e c"eaved as the
to parts &' >*ase(
18 r>*+ and 32
r>*+, the "atter !s
c"eaved as 28 r>*+and 5$8 r>*+$ /he
s'nthes!ed 5 r>*+
!"" &e transported !nto
n#c"eo"#s to =o!n the
assem&"' of the "arge
s#n!ts of r!&osome$
There is a ?7bp non$transcription -NA
fragment bet%een ad+acent rNA genes
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Assembly of ribosome
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. Nuclear matri'
*#c"ear matr!: !s ca""ed as n#c"eoske"eton that !s a meshork !n e#kar'ot!c
ce""s, that !s hat to"d 'o# &efore$ Beca#se n#c"ear matr!: !s assoc!ated !th
)*+ rep"!cat!on, >*+ transcr!pt!on and mod!f!cat!on, chromosome assem&"', andv!r#s rep"!cat!on, n#c"ear matr!: !s no pa!d more attent!ons to$
#omponents of nuclear matri',
① *onh!stone f!"aments at rat!o of 96@$ /he n#c"eoske"eton conta!ns three
scaffo"d prote!ns( , , and $Ⅰ Ⅱ Ⅲ
② + "!tt"e >*+ and )*+( /he >*+ !s !mportant to ma!nta!n the ske"eton
str#ct#re$ /he )*+ !s ca""ed as matr!: Ascaffo"d assoc!ated reg!on -;+> or +>.
here the +/ !s enr!ched to form the heterochromat!n &!nd!ng s!tes$
③ + "!tt"e phospho"!p!ds -1$6@. and s#gars -0$9@.$
*#c"ear ske"eton – n#c"ear "am!na – !nter f!"aments – pore comp"e: !s a
meshork s'stem !th ver' good sta&!"!t'$
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The function of nuclear skeleton,
1$ %resent the scaffo"ds for )*+ rep"!cat!on$ )*+ can &e anchored on to the
scaffo"d !th a rep"!cat!on "oop$ /he en'mes needed &' )*+ rep"!cat!on are
"ocated on the ske"eton, s#ch as )*+ po"'merase C, )*+ pr!merase, )*+
topo!somerase $
2$ s the p"ace here gene can &e transcr!pted and mod!f!ed$ /here are >*+
po"'merase &!nd!ng s!tes on the ske"eton$ *e s'nthes!ed >*+ !s com&!nedto the ske"eton for f#rther mod!f!cat!on$
3$ s assoc!ated !th the assem&"' of chromosome$ /he n#c"ear ske"eton ma'
&e same th!ng to chromosome ske"eton$ 30nm chromat!n f!&ers are
com&!ned to n#c"ear ske"eton to form "oops that !"" &e packaged f#rther !n ;
phase to &e assem&"ed as chromosome$
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#hromatin bound on nuclear skeleton or chromosome skeleton