F08-BCH361-L12

F08-BCH361-L12 - Translation in Eukaryotes 1 Main...

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1 Translation in Eukaryotes
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2 Main differences between translation in prokaryotes and eucaryotes involve Initiation
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3 ± thirteen more initiation factors are involved in initiation ± initial amino acid is methionine (not formylmethionine) ± special initial tRNAi is involved in initiation ± the first tRNA binds to the 40S subunit of the ribosome, before the mRNA binds to the complex ± there is no Shine-Dalgarno Sequence in eukaryotic mRNA ± the 5’ cap orients the the ribosome to the correct AUG codon by a scanning mechanism driven by ATP-Hydrolysis ± a poly-A binding protein (Pab1p) links the polyA tail to eIF- 4G and the pre initiation complex. Initiation :
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4 DNA Nucleus Processing hn-RNA ( h eterogeneous n uclear) Cytosol Ribosomes Protein
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5 Overview of the modifications, which the hn RNA undergoes to became the mature m-RNA hn-RNA introduction of the head-group removal of non coding sequences at the 3’ addition of poly- A Removal of Introns Fusion of Exons Transport into the cytosol, Translation 1 2 3
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6 adding of the Gpp (guanosine) cap and poly-A (adenosine) tail CAP Tail
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7 Methylguanosine (Gppp) head group. • Raw 5’ end of RNA: – Last nucleotide with 3 Phosphates on 5’ C. • Inverted GTP added to terminal phosphates by guanylyl transferase. – 2 phosphates are lost. – 5’ – 5’ triphosphate linkage. • Guanosine and internal nucleotide methylated by methyl transferase: – Guanosine on 7’ C. – Internal on 2’ C.
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8
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9 Structure of eukaryotic m-RNA Gpp (GTP)cap untransl coding sequences untransl polyA tail
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10
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11 The AUG codon is only recognized when it is in the right context: it must be surrounded by the Kozak Sequence: -3 ACC AUG G +4
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12 (A) eI Factor 2 with bound GTP binds the Met-tRNAi (B) eI Factors 1A and 3 bind to the 40S subunit forming the 43S preinitiation complex Step 1 (A) (B)
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13 (C) the m-RNA binds to the 43S preinitiation complex with the help of 4 further eI Factors: 4E binds to the GTP cap 4G binds 4A, 4E and 3 4A (ATPase) , helicase promotes mRNA binding 4B promotes helicase activity and mRNA Binding (C)
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This note was uploaded on 09/30/2011 for the course BCH 361 taught by Professor Fromme during the Fall '08 term at ASU.

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F08-BCH361-L12 - Translation in Eukaryotes 1 Main...

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