Split genes Exons and introns Chromatin structure and states Epigenetics 122114 1 Classification by nucleus Prokaryotes Organisms whose cells lack a nucleus Bacteria and Archaea ID: 915385
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Slide1
Review of the Molecular Biology of Genes in Eukaryotes
Split genes: Exons and intronsChromatin structure and states: Epigenetics
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1
Slide2Classification by +/- nucleus
Prokaryotes: Organisms whose cells lack a nucleusBacteria and ArchaeaStill have genomic DNA, but not in a specialized organelleEukaryotes: Organisms whose cells contain a nucleus
Protists, fungi, plants, animals, …
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Slide3Split genes and introns
The mRNA-coding portion of a gene can be split by DNA sequences that do not encode mature mRNAExons are the segments of a gene that code for mRNA, introns are
the segments of genes that do not encode mRNA.Introns are found in most genes in eukaryotes, also some in
Archaea
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Slide4R-loops can reveal introns
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5’
5’
5’
5’
Slide5Examples of R-loops in mammalian hemoglobin genes
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Slide6Types of exons
5
’
3
’
Start
Stop
Transcription start
Translation
Stop
polyA
5
’
untranslated
region
3
’
untranslated
region
5
’
3
’
Protein
coding
region
promoter
GT
AG
GT
AG
GT
AG
GT
AG
Open reading frame
Gene
mRNA
Translation
Initial exon
Internal exon
Internal coding exon
Terminal exon
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Slide7Human DMD
gene
7
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Slide8Introns are removed by splicing RNA precursors
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5’
5’
5’
Slide9Alternative splicing can generate multiple polypeptides from a single gene
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Slide10Alternative splicing can generate multiple polypeptides from a single gene, part 2
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Slide11Chromosomes and chromatin
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Slide12Chromosomes organize genes inside cells and enable their expression
Bind packaging proteins to DNA to make it more compact.Histones +DNA = chromatin in eukaryotes
Virion proteins in virusesDynamic, covalent modifications of histones are associated with active portions of chromosomes
Transcription
Regulation
Replication
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Slide13Bands and specialized regions of human chromosomes
Human chromosome 11:
125 Mb, 180
cM
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Slide14Human chromosomes, ideograms
Mitotic chromosomes are spread and stained with Geimsa. Those that stain are shown in black.
G-bands (more A+T rich).
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Slide15Human chromosomes, spectral karyotype
Reagents specific to each chromosome.
Chromosome
painting.
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Slide16Chromatin states in interphase nuclei
Adapted from
Makova and Hardison (2015) Nature Reviews Genetics
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Slide17Nucleosome core structure, 3D
146 bp duplex DNA wrapped around 8 histones molecules:
2 each of the dimers
H2A
-
H2B
,
H3
-
H4
N-terminal tails of histones emerge from the core
Luger et al. (1997) Nature 389: 251, Richmond lab
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Slide18Principal proteins in chromatin are histones
H3 and H4 : Arg rich, mostly conserved sequence
H2A and H2B : Slightly Lys rich, fairly conserved
H1 : very Lys rich, most variable in sequence
between species
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Slide19Histone structure and function
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Slide20Histone interactions via the histone fold
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Slide21Nucleosome core structure, 3D
146 bp duplex DNA wrapped around 8 histones molecules:
2 each of the dimers
H2A
-
H2B
,
H3
-
H4
N-terminal tails of histones emerge from the core
Luger et al. (1997) Nature 389: 251, Richmond lab
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Slide22Simplified view of nucleosomes
Linker: Sensitive to
micrococcal nuclease
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Slide23Alterations to chromatin structure are key steps in regulation
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Slide24Phosphorylation of histones
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Slide25Acetylation and Deacetylation of lysines in proteins
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Slide26Acetylation and d
eacetylation of histones
Co-activator EP300 is a HAT
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Slide27Epigenetic features
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Slide28Chromatin states in interphase nuclei
Adapted from
Makova and Hardison (2015) Nature Reviews Genetics
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