Gene%20Regulation%20results%20in%20differential%20Gene%20Expression,%20leading%20to%20cell%20Specialization

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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?vCiAyLPeCTMUfeature
  sharelistPLA2E1F3FFBFAE1CB6

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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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Organization of Typical Eukaryotic Genes
Fig. 18-8-3
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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
Promoter
Activators
Gene
DNA
Distal control element
Enhancer
TATA box
General transcription factors
DNA-bending protein
Group of mediator proteins
RNA polymerase II
RNA polymerase II
Transcription initiation complex
RNA 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 wont (but they are both
  still present)

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Fig. 18-10
Enhancer
Promoter
Albumin gene
Control elements
Crystallin gene
LENS CELL NUCLEUS
LIVER CELL NUCLEUS
Available activators
Available activators
Albumin gene not expressed
Albumin gene expressed
Crystallin gene not expressed
Crystallin gene expressed
(b) Lens cell
(a) Liver cell
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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
Exons
DNA
Troponin T gene
Primary RNA transcript
RNA splicing
or
mRNA
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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
Hairpin
miRNA
Hydrogen bond
Dicer
miRNA
miRNA- protein complex
3?
5?
(a) Primary miRNA transcript
Translation blocked
mRNA degraded
(b) Generation and function of miRNAs