condensacion del dna
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8/18/2019 Condensacion Del DNA
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Condensacion del DNA
Empaquetamiento del DNA en
la Cromatina
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3-99 JHW
HROMATIN
HROMATIN
Chromatin• Histone structure• Nucleosome
• Chromatin fber• Gene repression• Histone acetylation• Chromatin transcripti• Gene expression cont
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DNA compactioncompaction in a human nucleus
1bp (0.3nm
!0"000 nm
30nm
11
nm
Compaction o# DNA $% &istones Compaction $% c&romosome sca'old nuclear matri)
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Nuclear - chromosome compaction
Compaction $% c&romosome sca'old nuclear matri)
radial loopc&rosomosome model
!µm
! 0 µ m
chromatidchromatid
m i t o t i c c h r o m o s o m e
+ 2M NaCl
histones
+ 2M NaCl
histones
Mitosis
DNA loo
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HISTONES
are
highly conserved,small, basic proteins
H!
H*+
H*A
H3
H,
&eli)
aria$le
consered
Histone acetylation
is a reersi$le modicationo# l%sines in t&e N-terminio# t&e core &istones. Result/• reduced $indin to DNA• desta$ili1ation o# c&romati
2iner &istone
Core &istones
N
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ore
Histones
4&e $asic structure o# A22 core &istones is t&e same/• ! lon &%drop&o$ic alp&a-&eli)" $ordered $%
• * s&ort &%drop&o$ic alp&a &elices t&at #orm pairs• H*A - H*+ and H3 - H, 5&ic& interact.
Reerences! Moudrianakis et al. PNAS 88, 10138 (1991); PNAS 90, 10489 (1993); PNAS 92, 11170 (199)
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Histone octamer assembly
H3"H#tetramer
H2$"H2dimer
Histoneoctamer
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Histone octamer forms a ramp for
DNA
H, 5&iteH3 reenH*A li&t $lueH*+ dar $lue red/ 6 (ar" l%sorane/-7H (ser" t&r
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Histone octamer orani!es "#$ bp of
DNA
• Eac& core &istone dimer &as 8 DNA $indin sur#aces t&at orani1e 3 DNA turns
• 4&e &istone octamer orani1es !,: $p o# DNA in ! 3, &elical turn o# DNA/,; nm o# DNA pacaed in a disc o# 8 )!!nm
< 8 nm =
<
! ! n m
=
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hromatin
fibers
+ char&ed N termini($ind DNA on nei$orin
nucleosomes
hi&hly acetcore hi
(especiall% H3 a
30 nmchromatin fber
1'
• H)GH le*el o histone H1 • Reduced le*el o hist
• N &ene transcription • Gene transcription
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