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RNA Maturation and Processing

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(only exception: histones) ... Alternative splicing in different cell types ... Molecular definition of a gene ... – PowerPoint PPT presentation

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Title: RNA Maturation and Processing


1
RNA Maturation and Processing Stryer 6th Chapter
29/5th 28, Lodish 6th Chapter 4.2, 8.1/ 5th 4.2,
12.1
2
Gene organization, transcription, and translation
in prokaryotes
3
Gene organization, transcription, and translation
in eukaryotes
4
Bacterial operons produce polycistronic mRNAs
while most eukaryotic mRNAs are monocistronic and
contain introns
5
Capping enzyme adds a 5 cap and creates a 5 to
5 linkage
6
All mRNA precursors are polyadenylated (only
exception histones)
7
Simple and complex transcription units are found
in eukaryotic genomes
alternative splicing
8
(No Transcript)
9
Alternative splicing in different cell types
domains that bind to proteins in fibroblast
plasma membrane
10
(No Transcript)
11
Molecular definition of a gene
  • A gene is the entire nucleic acid sequence that
    is necessary for the synthesis of a functional
    polypeptide
  • DNA regions that code for RNA molecules such as
    tRNA and rRNA may also be considered genes
  • In eukaryotes, genes lie amidst a large expanse
    of nonfunctional, noncoding DNA and genes may
    also contain regions of noncoding DNA (introns)

rRNA gene cluster in E. coli
12
Exon-intron structure in eukaryotic genomes
Exon
Yeast 6,000 genes Humans 25,000 genes
(1.5 encode for proteins, 1.5 encode for RNAs.
Rest is junk DNA (97 of our genome)
Intron
13
Signal sequences for splicing
14
Point mutations can affect exon-intron boundaries
in-frame STOP codon in intron
Mutation creates new 5 splice site
message is spliced incorrectly (STOP codon
becomes part of coding sequence)
low hemoglobin-beta production resulting in anemia
15
RNA splicing
In ciliate rRNA
In humans
16
Spliceosome mediated intron removal
17
Catalysis is driven by small nuclear RNAs, not
primarily by proteins
18
  • What you need to know
  • Pre m-RNA is processed by
  • adding a cap to the 5 end (only known 5 to 5
    link in nucleic acid)
  • the cap is important for translation initiation
  • 2) polyadenylation, which is thought to
    increase mRNA half-life
  • splicing (group I, II self-splicing, or
    spliceosome-assisted.
  • Spliceosome composed of snRNPs, which
    contain snRNAs)
  • snRNAs drive the reaction, not the proteins.
    Different steps can be
  • carried out in the test tube and do not require
    protein to be present.
  • alternative splicing provides tissue-specific
    protein variants
  • Introns are encoded in the DNA. In the mRNA
    transcript, they can be
  • recognized as 5splice site, branch point and
    3splice site. The intron
  • begins with GU and ends with AG. The branch
    point is usually an A.
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