Gene Regulation results in differential Gene Expression, leading to cell Specialization
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GENE REGULATION RESULTS IN DIFFERENTIAL GENE EXPRESSION, LEADING TO CELL SPECIALIZATION
Eukaryotic DNA
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Epigenetics – Ghost in Your Genes Watch to see how your environment and
your choices influence inheritance… http://www.youtube.com/watch?v=CiAyL
PeCTMU&feature=share&list=PLA2E1F3FFBFAE1CB6
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Differential Gene Expression Nucleosome Packing: DNA
wraps around histone proteins to form a structure called a nucleosome. Nucleosomes help pack DNA into eukaryotic chromosomes. When acetyl groups attach to
the histone proteins the DNA in chromosomes loosens to allow for transcription.
The addition of methyl groups to histone proteins can cause DNA to condense thus preventing transcription.
In Genomic Imprinting, methylation regulates expression of either the maternal or paternal alleles of certain genes at the start of development.
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Fig. 18-8-3
Enhancer(distal control
elements)
Proximalcontrol
elements
Poly-A signal
sequenceTermination
region
DownstreamPromote
r
Upstream
DNAExonExon ExonIntro
nIntro
n
Exon Exon ExonIntron
Intron Cleaved 3
endof primarytranscript
Primary RNA
transcript
Poly-A
signal
Transcription
5 RNA
processingIntron
RNA
Coding segmentmRN
A5
Cap
5 UTR
Startcodon
Stopcodon 3
UTR
Poly-A
tail
3
Organization of Typical Eukaryotic Genes
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The Roles of Transcription Factors Regulatory Proteins, repressors and
activators, operate similarly to those in prokaryotes, influencing how readily RNA polymerase will attach to a promoter region. In many cases, numerous activators are acting in concert to influence transcription.
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Fig. 18-9-3
Enhancer
TATA
box
Promoter
ActivatorsDN
A
Gene
Distal control
element
Group ofmediator
proteins
DNA-bending
protein
Generaltranscripti
onfactors
RNApolymerase
II
RNApolymerase
II
Transcriptioninitiation
complexRNA
synthesis
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Coordinately controlled eukaryotic genes
A particular combination of control elements can activate transcription only when the appropriate activator proteins are present.
All cells of an organism have all chromosomes/genes but certain genes are only active in certain cells. The transcription factors present in the cell determine which genes will be active and which won’t (but they are both still present)
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Fig. 18-10
Controlelemen
ts
Enhancer
Available
activators
Albumin gene
(b) Lens cell
Crystallin gene
expressed
Available
activators
LENS CELLNUCLEUS
LIVER CELL
NUCLEUS
Crystallin gene
Promoter
(a) Liver cell
Crystallin gene
not expressed
Albumin gene
expressed
Albumin gene
not expressed
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Post Transcriptional Regulation Alternate Gene Splicing - different
mRNA molecules are produced from the same primary transcript, depending on which RNA segments are treated as exons and which as introns
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Fig. 18-11
or
RNA splicing
mRNA
PrimaryRNAtranscri
pt
Troponin T gene
Exons
DNA
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Noncoding RNAs role in gene expression
RNA Interference, noncoding RNAs play multiple roles in controlling gene expression. MicroRNAs (miRNAs) and Small inserting RNAs (siRNAs) are small single-stranded RNA molecules that can bind to mRNA. These can degrade mRNA or block its translation. The difference between the two is that they form from different RNA precursors.
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Fig. 18-13
miRNA-proteincomple
x(a) Primary miRNA
transcript
Translation blocked
Hydrogen
bond
(b) Generation and function of miRNAs
Hairpin
miRNA
miRNA
Dicer
3
mRNA degraded
5