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今天的科學新知有哪些?請舉出印象最深刻的例子

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今天的科學新知有哪些?請舉出印象最深刻的例子

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一群大學生熱烈討論著NBA

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•Proteins are in a dynamic state in which they are turned over often

•Abnormal proteins that are formed from errors in either transcription or translation are degraded quickly

•Pathways are restricted to:

•lysosomes

•proteasomes

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Translation kinetics and protein folding

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•Protein Synthesis Makes Memories

•蛋白質合成與記憶形成

•記憶分為兩種類型——短期和長期。短期記憶持續時間為幾秒至幾分鐘，而長期記憶可以持續數天、數月，甚至一生。

當你在派對上遇到某人並告訴你她的名字時，你可能幾秒鐘後就忘記了。然而，你最好的朋友的名字轉化為長期記憶，可能會持續一生。

形成長期記憶依賴於新的蛋白質合成。給予阻斷蛋白質合成的藥物的動物無法形成新的長期記憶，但它們形成短期記憶的能力是保留的。也許擁有良好長期記憶的人更擅長製造新的腦部蛋白質。

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In the box, the peptidyl transfer mechanism is catalyzed by RNA.

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•N-formylmethionine in prokaryotes is ________

•Specific bonds in precursors are _________, as in the _________of preproinsulin to proinsulin and of proinsulin to insulin

•____________ are ________ by specific proteases associated with the endoplasmic reticulum

•Finished protein enters the Golgi apparatus, which directs it to its final destination

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HIF 缺氧時的調節方式與ubiquitination 關係

HIF-α 的降解機制（在正常氧氣濃度下）

1. Pro564 被 proline hydroxylase 羥化

2. 結合 pVHL（腫瘤抑制因子）

3. 結合 泛素連接酶（UL） → 加上 泛素（ubiquitin）

4. 送入蛋白酶體進行降解

在缺氧狀況下，兩個羥化反應都會受到抑制：

沒有脯胺酸羥化 ➔ HIF-α 不會被降解

沒有天門冬胺酸羥化 ➔ HIF-α 可參與轉錄

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Summary of the Steps in Chain Elongation

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Shine–Dalgarno Sequence

1. RBS ____________________________________(全名)

2. Binds to a _______________-rich sequence on the ____S ribosomal RNA part of the ____S subunit

3. Aligns it for proper translation beginning with the ______ codon

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•Synthesis of polypeptide chain starts at the N-terminal end

•Chain grows from N-terminus to C-terminus

•In prokaryotes, the initial N-terminal amino acid of all proteins is N-formylmethionine (fmet)

•Aminoacyl-tRNAs that tRNAmet and tRNAfmet form with methionine are called met-tRNAmet and met-tRNAfmet, respectively

•Methionine must be bound to tRNAfmet to be formylated

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•Cysteine residue in which the ___ atom has been replaced by a _____ atom

•Only amino acid that lacks its own ___________and is synthesized while bound to its tRNA

Codon is ________

思考題:為何稱為第21個胺基酸?

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•Stop signals - Codons UAA, UAG, and UGA,

•Release factors - RF-1-UAA and UAG

RF-2- UAA and UGA

•GTP, which is bound to RF-3

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Ubiquitin-activating enzyme (E1)

Ubiquitin-carrier protein (E2)

Ubiquitin-protein ligase (E3)

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發生在splicing時.......

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•Step 1 - Assembly of a 43S preinitiation complex

•Step 2 - Recruitment of mRNA

••Step 3 - Recruitment of the 60S ribosome, forming the 80S initiation complex

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Polysomes (Polyribosome)

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•Cofactors, such as heme groups, are ______

•Disulfide bonds are ______

•Some amino acid residues are covalently _________ (Example - Conversion of proline to hydroxyproline)

•Other covalent modifications can occur (Example - Addition of ___________ or lipids to yield an active final form of the protein in question )

•Proteins can also be methylated, phosphorylated, arginylated, and ubiquitinylated

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高立圖書版權

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Degradation of Proteins with Acidic N-Termini

記得N-end rule pathway（N端法則）嗎?

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原來intron的差異也會造成不同的表現型<

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原來intron的差異也會造成不同的表現型

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tmRNA

•tmRNA because it acts partly like tRNA and partly like mRNA. Like a tRNA, the tmRNA carries alanine, an amino acid. When it finds a stalled ribosome, it binds beside the defective mRNA.

思考題: 完成的蛋白可以提供細胞使用嗎?

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Posttranslational Modification of Proteins

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Studying Chain Elongation

•Puromycin is a structural analog for the 3′ end of an aminoacyl-tRNA

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Various Shine-Dalgarno Seq.

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Chain Initiation: tRNA Sequence

•3′-UAC-5′

tRNAfmet recognizes the AUG triplet (start signal)

• tRNAmet recognizes the AUG triplet when it is found in an internal position in the mRNA sequence

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•Misfolded proteins can be repaired by eukaryotic chaperones

•Can be targeted for destruction by ubiquitination

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Eukaryotic Translation: Chain Elongation

•Uses the same mechanism of peptidyl transferase and ribosome translocation as prokaryotes

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The tRNA Occupies Three Sites During Elongation of the Polypeptide

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Initiation complex include:

•Initiation codon (AUG) of mRNA

•fmet-tRNAfmet

•30S and 50S ribosomal subunits

•GTP

•Three protein initiation factors, which are IF-1, IF-2, and IF-3

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Chain Termination

•Only one release factor binds to all three stop codons (UAG, UAA, or UGA)

•Suppressor tRNA: Permits translation to continue through a stop codon

•Found in cells in which a ______ has introduced a stop codon

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Eukaryotic Translation: New Evidence

•Nucleus has all the components necessary for translation

•In isolated test systems, proteins are translated in the nucleus

•AUG is not always the start codon

•Peptides that are synthesized to be presented on the surface of the major histocompatibility complexes use_______as the start codon

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•Step 1

•Addition of the second amino acid

•Second aminoacyl-tRNA binds at the A site

•Step 2

•Requires _______ and three protein elongation factors, ___, _____ (temperature-unstable), and ______ (temperature-stable)

•GTP is hydrolyzed

•EF-Tu

•EF-P

•EF-Ts

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•Step 3

•Peptide bond is formed in a reaction catalyzed by peptidyl transferase

•Step 4 - Translocation

•Peptidyl-tRNA is translocated to the vacant site from the _ site

•______ is required

•ATP or GTP??