Transcript Part2
The Transport of Molecules
into and out of the Nucleus
• Through an aqueous channels whose
diamenter is adjustable
• Bidirection: import and export
• Active and passive transportation
• Localization signal dependnet
NPC
Nuclear Localization Signals,NLS
microinjection
T-antigen
Steroid hormone
Nuclear Export Signals, NES
mRNP
The HIV Rev protein, which contains a NES, can
override the restriction against transporting premRNAs with unspliced splice sites
• Proteins imported to or exported from
the nucleus contain NLS or NES.
Proteins that shuttle between the
nucleus and cytoplasm contain both
signals.
• Pre-mRNAs bound by a spliceosome
normally are not exported from the
nucleus, assuring that only fully
processed, functional mRNAs reach the
cytoplasm for translation.
• Macromolecules are actively transported
into and out of the nucleus through
nuclear pores.
Differences between nuclear pores
transportation and transmembrane
transportation
• It occurs through a large, regulated
aqueous pore rather than through a
protein transporter that spans one or
more lipid bilayers.
• It is thought that a nuclear protein is
transported through the pores while it is
in a fully folded conformation; by
contrast, proteins have to be unfolded
during their transport into other
organelles.
• The localization signal will not be cut off
after transportation. This is
indispensable for nuclear reconstruction
following mitosis.
Nucleolus
• The appearance of the nucleolus
changes drammatically during the cell
cycle.
nucleolus changes
rRNA of nucleolus
• Nucleolar fusion
• The ribosomal RNA gene are located near
the tips of each of 5 different chromosomes
(NORs)
• cell contains multiple copies of the rRNA
genes
• Because of their repeating arrangement,
and because they are transcribed at a
very high rate, the tandem arrays of
rRNA genes can easily be seen in
spread chromatin preparations.
• The rRNA genes are transcribed by RNA
polymerase I, and each gene produces
the same primary RNA transcript. In
humans this primary RNA transcript,
known as 45S rRNA.
• Before it leaves the nucleus in
assembled ribosomal particles, the 45S
rRNA is cleaved to give one copy each
of the 28S rRNA, the 18S rRNA, and the
5.8S rRNA of the final ribosome.
• The derivation of these three rRNAs
from the same primary transcript
ensures that they will be made in equal
quantities.
• The remaining part of each primary
transcript is degraded in the nucleus.
• The 5S rRNA genes are transcribed by
RNA polymerase III (a number of other
genes encoding small stable RNAs,
most notably the transfer RNA [tRNA]
genes, are also transcribed by RNA
polymerase III )
Procedure of ribosome assemblage
• the intact 45S transcript is first
packaged into a large complex
containing many different proteins
imported from the cytoplasm.
• These components remain in the
nucleolus when the ribosomal subunits
are exported to the cytoplasm in
finished form.
• As the 45S rRNA molecule is processed,
it gradually loses some of its RNA and
protein and then splits to form separate
precursors of the large and small
ribosomal subunits.
• 18S rRNA integrated into small
ribosomal subunits, and 28s,5.8S,5S
rRNA integrated into large ribosomal
subunits.
• The last steps in ribosome maturation
occur only as these subunits are
transferred to the cytoplasm. (This
delay prevents functional ribosomes
from gaining access to the incompletely
processed hnRNA molecules in the
nucleus.)
染色体 染色体DNA
复制源:DNA复制起始点
使染色体能够进行复制
着丝粒:姐妹染色单体连接部位
细胞分裂时使两拷贝分离
端 粒:染色体末端
保证DNA复制的完整性
染色体蛋白 组蛋白
H2A H2B H3 H4—核小体
H1 — 染色体高级结构
非组蛋白
染色体组装:不同结构水平
染色质的种类:常染色质和异染色质的区别
总结3
核被膜
外核膜
结构:与内质网膜连续
表面有骨架成分分布
功能:与蛋白合成有关
总结1
内核膜
分布:内核膜内表面
核纤层 组成:核纤层蛋白
功能:间期 染色质锚定
分裂期 调控核膜
核间隙
核孔 结构:核孔复合体
功能:核内外物质转运
大分子
小分子
核基质 结构:核骨架
功能:
核仁 结构:三个特征性功能区
纤维中心 rDNA
总结2
(核仁组织者)
原纤维成分 rRNA
颗粒成分 成熟的rRNA前体
功能:rRNA 合成、加工
核糖体装配