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2006 年化学诺贝尔奖

2006 年化学诺贝尔奖. 科恩伯格现年 59 岁，目前供职于美国斯坦福大学医学院，他的父亲阿瑟 · 科恩伯格是 1959 年的诺贝尔医学或生理学奖得主之一。科恩伯格揭示了真核生物体内的细胞如何利用基因内存储的信息生产蛋白质，而理解这一点具有医学上的“基础性”作用，因为人类的多种疾病如癌症、心脏病等都与这一过程发生紊乱有关。. 罗杰 · 科恩伯格. H protein synthesis. H1 The genetic code H2 Protein synthesis(translation) in prokaryotes

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2006 年化学诺贝尔奖

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  1. 2006年化学诺贝尔奖 科恩伯格现年59岁，目前供职于美国斯坦福大学医学院，他的父亲阿瑟·科恩伯格是1959年的诺贝尔医学或生理学奖得主之一。科恩伯格揭示了真核生物体内的细胞如何利用基因内存储的信息生产蛋白质，而理解这一点具有医学上的“基础性”作用，因为人类的多种疾病如癌症、心脏病等都与这一过程发生紊乱有关。 罗杰·科恩伯格

  2. H protein synthesis • H1 The genetic code • H2 Protein synthesis(translation) in prokaryotes • H3 Translation in eukaryotes • H4 Protein targeting • H5 Protein glycosylation

  3. H1 The genetic code • The genetic code is a triplet code • The genetic code is degenerate • Universality of the genetic code • Reading frames • Open reading frames

  4. 1. Triplet code • The relationship between the nucleotide sequence of the mRNA and the amino acid sequence of the polypeptide is called the genetic code.

  5. Triplet code • The three nucleotides in group called codon • 43=64 codons • Initiation codon (AUG) • stop codon ( UAA, UAG,UGA) • New codon: UGA Se-cysteine

  6. Triplet code

  7. 2.The genetic code is degenerate • There are 64 codons, but only 20 amino acids. • Degenerate: A single amino acid is coded for by several different codons. • Synonyms: Different codons that specify the same amino acid.

  8. Degeneracy of the genetic code

  9. Codon and anticodon • Anticodon: a triplet of bases in a specific tRNA molecule. • Each base in the codon base pairs with its complementary base in the anticodon. • Wobble base-pairing

  10. 3.Universality of the genetic code • All living organism used almost the same code. • But there are a few differences. E.g. in mitochondrial mRNAs, some codons have different meanings.

  11. Different code

  12. 4.Reading frames • Start: UAG • Stop: UAA, UAG, UGA • Unit: Triplet • Character: Continuous

  13. mutant

  14. 5.Open reading frames • An open reading frame (ORE) is a run of codons that starts with ATG and ends with a termination codon, TGA TAA or TAG.

  15. To identify potential coding regions. • Coding regions of genes contain relatively long ORFs unlike noncoding DNA where ORFs are comparatively short.

  16. H2 translation in prokaryotes • Overview • Synthesis of aminoacyl-tRNA • Initiation of protein synthesis • Elongaion • Termination

  17. 1. Overview • Direction: mRNA: 5’—3’, • Protein: N—C • Site: ribosome • Recognizing: Codon (mRNA) base pairs anticodon (tRNA) via hydrogen bonding • Translation phase: initiation, elongation and termination.

  18. 2. Synthesis of aminoacyl-tRNA(amino acid activation) Each tRNA molecule has a cloverleaf secondary structure consisting of three stem loops, one of which bears the anticodon at its end.

  19. The amino acid is covalently bound to the 3’ OH group at the 3’ end by aminoacyl synthetase to form aminoacyl-tRNA. The reaction is called amino acid activation. • tRNAGly Gly-tRNAGly

  20. Question • There are 61codons, 20 amino acids. • How many are there tRNA and aminoacyl-tRNA synthetase?

  21. Synthesis of aminoacyl-tRNA is crucially important for two reasons • First : each amino acid must be covalently linked to a tRNA molecule in order to take part in protein synthesis,which depend upon the adaptor function of tRNA. • Second: the covalent bond is a high energy bond that enables the amino acid to react with the end of the growing polypeptide chain.

  22. The synthesis reaction occurs in two steps • The first step is the reaction of amino acid and ATP to form an aminoacyl-AMP. • The second step is the aminoacyl group of aminoacyl-AMP is transferred to the 3’end of the tRNA molecule to form aminoacyl-tRNA.

  23. step one

  24. Step two:Aminoacyl-AMP+tRNA-----aminoacyl-tRNA +AMP

  25. 3.Initiation of protein synthesis • Each ribosome has three binding sites for tRNAs; an A site where the incoming aminoacyl-tRNA binds, a P site where the tRNA linked to the growing polypeptide chain is bound, and an E site which binds tRNA prior to its release from the ribosome .

  26. Initiation • Translation in prokaryotes begins by the formation of a 30S initiation complex between the 30S ribosomal subunit, mRNA, initiation factors and fMet tRNA fmet . The 30S subunit binds to the Shine-Dalgarno sequence which lies 5' to the AUG Start codon and is complementary to the 16S rRNA of the small ribosomal subunit.

  27. Initiation • The ribosome then moves in a 3' direction along the mRNA until it encounters the AUG codon. The 50S ribosomal subunit now binds to the 30S initiation complex to form the 70S initiation complex. In this complex, the anticodon of the fMet-tRNA fMet is base-paired to the AUG initiation codon (start codon) in the P site.

  28. fMet-tRNAfMet

  29. 4. Elongation • Elongation of the polypeptide chain occurs in three steps: • 1.Aminoacyl-tRNA binding • 2.Peptide bond formation • 3.Translocation

  30. Elongation Factor Tu(EF-Tu)

  31. 5.Termination • Termination codons: UAA, UAG, UGA • Release factors: RF1, RF2, RF3 • RF1 UAA,UAG RF2 UGA • RF3 RF3

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