Transcript Gene Regulation results in differential Gene Expression, leading to

GENE REGULATION RESULTS
IN DIFFERENTIAL GENE
EXPRESSION, LEADING TO
CELL SPECIALIZATION
Eukaryotic DNA
Epigenetics – Ghost in Your Genes
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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.
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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.
Fig. 18-8-3
Organization of Typical Eukaryotic Genes
Enhancer
(distal control elements)
Poly-A signal
sequence
Proximal
control elements
Termination
region
Exon
Intron
Exon
Intron
Exon
DNA
Upstream
Promoter
Primary RNA
5
transcript
Downstream
Transcription
Exon
Intron
Exon
Intron
Exon
RNA processing
Cleaved 3 end
of primary
transcript
Poly-A
signal
Intron RNA
Coding segment
mRNA
3
5
Cap 5
UTR
Start
codon
Stop
codon
3
UTR Poly-A
tail
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.
Fig. 18-9-3
Promoter
Activators
DNA
Enhancer
Distal control
element
Gene
TATA
box
General
transcription
factors
DNA-bending
protein
Group of
mediator proteins
RNA
polymerase II
RNA
polymerase II
Transcription
initiation complex
RNA synthesis
Coordinately controlled eukaryotic genes
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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)
Fig. 18-10
Enhancer
Control
elements
Promoter
Albumin gene
Crystallin gene
LIVER CELL
NUCLEUS
LENS CELL
NUCLEUS
Available
activators
Available
activators
Albumin gene
not expressed
Albumin gene
expressed
Crystallin gene
not expressed
(a) Liver cell
Crystallin gene
expressed
(b) Lens cell
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
Fig. 18-11
Exons
DNA
Troponin T gene
Primary
RNA
transcript
RNA splicing
mRNA
or
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.
Fig. 18-13
Hairpin
miRNA
Hydrogen
bond
Dicer
miRNA
5 3
(a) Primary miRNA transcript
mRNA degraded
miRNAprotein
complex
Translation blocked
(b) Generation and function of miRNAs