大学课程英汉对照分子生物学导论教学Chapter 5课件

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2. Helps transport into cytoplasm 帮助转运到细胞质中
Discussed in Chapter 7
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3. Enhances translation / 增强转译
Cap-binding protein
No translation occurs.
Normal Self-splicing splicing
With help of proteins
U6 U1 U2 A
U4
U5
Without help of proteins
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5.3.4 Trans-Splicing / 反式剪接
RNA piece of separate origin
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snRNPs: small nuclear ribonucleoproteins
snRNPs are small particles found in the nucleus and contain both protein and RNA. snRNPs functioning in splicing: U1, U2, U4, U5 and U6.
after transcription.
系列修饰。
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Chapter 5 mRNA Modifications
in Eukaryotes 第5章 真核生物mRNA的修饰
5.1 Capping 5.2 Polyadenylation 5.3 Splicing 5.4 mRNA Editing 5.5 Experiments
AAAAAAA - - - - - - AAAA
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5.3 Splicing / 剪接
Exons: Parts of a gene that are expressed as protein. Introns: Sequences that do not code for protein and interrupt the coding regions. Splicing: The process of removing introns
Poly(A) tail
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The polyadenylation signal / 聚腺苷酸化信号
Polyadenylation signal has a typical sequence of AAUAAA. This sequence gives an instruction as “to cut the mRNA about 20 nucleotides downstream, near a GU-rich sequPernec-me”R. NA
DNA Mature mRNA Protein
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Trans-Splicing / 反式剪接
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5.3.5 Reasons for Introns 内含子存在的原因
Introns-early theory
Intron: “Why am I here?”
U
G
Exon 1
G
5’
Intron
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4. Helps remove the first intron 帮助去除第一个内含子
The first intron
RNA
DNA
RNA polymerase II
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5.2 Polyadenylation / 聚腺苷酸化
Polyadenylation is a modification process in which a string of about 250 adenine nucleotides is added to the 3’ end of the transcript.
Pre-mRNA
Polyadenylation
AAAAAAA - - - - - - AAAA
Poly(A) tail
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Polyadenylation does not occur at the natural end
Pre-mRNA
Polyadenylation
AAAAAAA - - - - - - AAAA
Guanylyl transferase
DNA
RNA polymerase II
Proteins for polyadenwk.baidu.comlation at CTD
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Functions of the poly(A) tail poly(A)尾的功能
The main function of poly(A) tail is to protect the mRNA from degradation by ribonucleases.
5.1 加帽 5.2 聚腺苷酸化 5.3 剪接 5.4 mRNA编辑 5.5 实验研究
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5.1 Capping / 加帽
An mRNA that has been transcribed but is not yet ready for translation is called a pre-mRNA, or a primary transcript.
AAAAAAA - - - - - - AAAA
AAAAAAA - - -
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Functions of the poly(A) tail poly(A)尾的功能
There is also some evidence that the poly-A tail is involved in splicing and enhances translation of mRNAs.
CFI (cleavage factor I)
CFII (cleavage factors II)
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Poly(A)-Binding Protein
CTD: C-terminal domain
Proteins for capping at CTD
Methyl transferase
RNA triphosphatase
Tetrahymena thermophilia [tetrəhaimənə]嗜热四膜虫 [θə:məfailiə]
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Self-splicing of group I intron
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Self-splicing of group II intron II 类内含子的自我剪接
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Functions of the cap structure 帽结构的功能
1. Helps prevent degradation 帮助防止降解
2. Helps transport into cytoplasm 帮助转运到细胞质中
3. Enhances translation / 增强转译
4. Helps remove the first intron 帮助去除第一个内含子
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1. Helps prevent degradation 帮助防止降解
RNase
5’-3’ phospho diester bond
RNase
5’-3’ phospho diester bond
5’-5’ triphosphate bond
Introns-late theory
A
Exon 2 3’
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Intron-early theory / 内含子早现说
E. coli
“I heard somebody say E. coli once had introns. Is that true?”
“Could be. Who knows?!”
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Drosophila Dscam gene
[drəusɔfilə]
Exon 4
Exon 6
Exon 9
Exon 3
4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10 4.11 4.12
5’ AG/GUAUGU…body of intron…UACUAAC-YAG / 3’
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The basic splicing reaction
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5.3.2 Proteins involved in Splicing 在剪接中发挥作用的蛋白质
Spliceosome: The collection of factors, especially snRNPs, that help with the splicing of introns.
Chapter 5 mRNA Modifications
in Eukaryotes 第5章 真核生物mRNA的修饰
In prokaryotes,
在原核生物中，转录产
transcription produces a 生的mRNA几乎是
nearly exact mRNA copy of DNA的准确拷贝，并且
5’-Cap
RNA DNA
RNA polymerase II
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Capping process / 加帽过程
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CTD: C-terminal domain
Methyl transferase
RNA triphosphatase
Guanylyl transferase
DNA
RNA polymerase II
Capping is the process of adding a derivative of guanine nucleotide to the 5’ end of the pre-mRNA.
一条已经转录出来但 还没有准备好用于转 译的mRNA称为前体 mRNA或初级转录本。
加帽是在前体mRNA 的5’末端加上一个鸟 嘌呤核苷酸衍生物的 过程。
AAUAAA
GU
Polyadenylation
AAAAAAA - - - - - - AAAA
Poly(A) tail
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The cleavage complex / 切割复合体
Cleavage complex
CPSF (cleavage and polyadenylation specificity factor) CstF (cleavage stimulation factor)
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RNA in snRNP
5’ Exon
UCCAUACA AGGUAUGU
3’ Intron
5.3.3 Self-Splicing / 自我剪接
Splicing that occurs without the help of proteins or snRNPs is called self-splicing.
the DNA, and the transcript 这一转录产物会立即被
is immediately translated 转译成蛋白质。在真核
into protein. In eukaryotes, a series of modifications
生物中，转录时以及转
occur to mRNA during and 录后会对mRNA进行一
from a pre-mRNA.
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5.3.1 The Basic Splicing Reaction 基本的剪接反应
Splice sites: Sequences that mark the beginning and ends of introns and exons.
Splice sites in yeast
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Intron-late theory / 内含子后现说
E. coli
“We are the ones having introns! We are proud of it.”
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Alternative splicing / 可变剪接
Alternative splicing: a kind of splicing that can produce various proteins from one gene.
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Structure of the cap / 帽的结构
5’-3’ phosphodiester bond
5’-5’ triphosphate bond
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RNA polymerase II
Discussed in Chapter 4
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Capping takes place quite early.