Lec4_3_web

Lec4_3_web - Introduction to RNA Structure Unique Aspects...

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Unique Aspects of RNA Structure : 1. C2’ OH group (alkaline hydrolysis). 2. Sugar Pucker – C3’-endo. 3. Helix is A-form. 4. There are unusual H-bonding pairs – for example, non-Watson-Crick pairs, base triplets. Introduction to RNA Structure
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RNA Classification . There are three major classes of RNA. 1. Ribosomal RNA or rRNA. 1. Transfer RNA or tRNA. 1. Messenger RNA or mRNA.
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23S (2900 nt) 28S (~5000 nt) 16S (1540 nt) 18S (1900 nt) 5S (120 nt) 5.8S (160 nt) 5S (120 nt) Prokaryotes Eukaryotes rRNA
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tRNA: - Prokaryotes and Eukaryotes – 4S (75- 95 nt). mRNA : Prokaryotes: 7S-30S (200-5000 nt) Eukaryotes: 10S-45S (500-20,000 nt)
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tRNA is a good model because the structural details are well-known. tRNA provides a good demonstration of unique aspects of RNA structure. First, note that the structures on the following panels are in two-dimensions. - The single chain loops back on itself and forms regions that are H-bonded (duplexed) and regions that are not H-bonded. - This pattern leads to “loops”, where there is no H- bonding, and “stems”, where the bases H-bond. - This structure is referred to as the “cloverleaf” structure.
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There are 4 stem regions, each of which contain 4-7 Watson-Crick base-pairs organized into double helices. 1. Acceptor Stem 2. Anticodon Stem 3. D Stem 4. Ψ Stem
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Acceptor Stem D Stem D Loop XYZ Anticodon Loop Anticodon Triplet Anticodon Stem Variable Loop Site of amino acid attachment T Ψ C Loop Ψ Stem C-C-A OH N N 1 2 3 4 5 6 O H O H H H H 5’ N N O H O H Ribose 1 2 3 4 5 6
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Acceptor Stem : - Locus of both the 3’ and 5’ termini. - Carries a triplet C-C-A at the 3’ end. - Attached to the O3’H of Adenine is a specific amino acid corresponding to the sequence of the anticodon base-triplet in the anticodon loop. D and Ψ Stems : - The loops neighboring these stems contain dihydrouridine (D) and pseudouridine ( Ψ ). - All tRNA have conserved dihydrouridine or pseudouridine, which are modified nucleotides. We’ll come back to these later.
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Variable Loop : - The number of nucleotides in stems and loops is generally constant except for the variable loop. -
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This note was uploaded on 09/11/2008 for the course BCH 453 taught by Professor Clark during the Fall '08 term at N.C. State.

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Lec4_3_web - Introduction to RNA Structure Unique Aspects...

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