Gene Expression

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Gene Expression

• Ch 11

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Gene expression

• Genes to proteins
• Genotype to phenotype
• Produce specific proteins when and where they are
  needed

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lac Operon

• E. Coli make enzymes to utilize lactose sugars
• Dependent on presence/absence of lactose
• 3 enzymes to take up and metabolize lactose
• Genes that code for enzymes located next to each
  other in DNA

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Fig. 11-1b
OPERON
Regulatory gene
Promoter Operator
Lactose-utilization genes
DNA
mRNA
RNA polymerase cannot attach to promoter
Active repressor
Protein
Operon turned off (lactose absent)
DNA
RNA polymerase bound to promoter
mRNA
Protein
Enzymes for lactose utilization
Inactive repressor
Lactose
Operon turned on (lactose inactivates repressor)
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lac Operon

• Control sequence
• Promoter
• Operator
• Operon
• Genes, promoter and Operator
• Exist almost solely in prokaryotes

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lac Operon

• Repressors
• Block RNA polymerase from binding
• Regulatory genes code for repressors
• Located outside the operon

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Fig. 11-1b
OPERON
Regulatory gene
Promoter Operator
Lactose-utilization genes
DNA
mRNA
RNA polymerase cannot attach to promoter
Active repressor
Protein
Operon turned off (lactose absent)
DNA
RNA polymerase bound to promoter
mRNA
Protein
Enzymes for lactose utilization
Inactive repressor
Lactose
Operon turned on (lactose inactivates repressor)
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Trp Operon

• trp operon
• repressor is inactive alone
• When tryptophan present, binds to repressor,
  enabling it to switch transcription off

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Fig. 11-1c
Promoter
Operator
Gene
DNA
Active repressor
Active repressor
Tryptophan
Inactive repressor
Inactive repressor
Lactose
trp operon
lac operon
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Differentiation

• Specialized in structure and function
• Results from selective gene expression
• Variety of cell types, expressing different
  combination of genes

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Differentiation

• Differentiated cells may retain all of their
  genetic potential
• Most differentiated cells retain a complete set
  of genes

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The Chromosome

• Packaging helps regulate expression
• Histone proteins
• Aid in packaging and ordering DNA

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The Chromosome

• Nucleosome
• DNA-histone complex involving DNA wound around 8
  histone protein core
• Resembles beads on a string
• Linkers
• Join consecutive nucleosomes
• Packing presumably prevents access of
  transcription proteins

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Proteins controlling transcription

• Regulatory proteins turn off/on gene
  transcription
• Transcription factors
• Enhancers
• Silencers
• RNA splicing

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Proteins controlling transcription

• Enhancers
• Activators bind and bend DNA
• Interact with other transcription factor proteins
• Bind as complex to promoter
• Silencers
• RNA splicing

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Proteins controlling transcription

• Silencers
• Bind to DNA and inhibit start of transcription

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Splicing

• Alternate RNA splicing
• Splicing can occur in more than 1 way
• Different mRNA from same RNA transcript

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Small RNAs

• miRNA
• RNA interference

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Protein
miRNA
miRNA- protein complex
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Target mRNA
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3
Translation blocked
OR
mRNA degraded
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Regulation of translation

• Breakdown of mRNA
• Initiation of translation
• Protein activation
• Protein breakdown

Folding of polypeptide and formation of SS
linkages
Cleavage
Initial polypeptide (inactive)
Folded polypeptide (inactive)
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Cascades
Egg cell
Egg cell within ovarian follicle
Protein signal

• Protein products from one set of genes activate
  another set
• Homeotic gene

Follicle cells
Gene expression
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Head mRNA
Cascades of gene expression
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Embryo
Body segments
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Gene expression
Adult fly
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Signal transduction pathways
Signaling cell
Signalmolecule

• Series of molecular changes that converts signal
  on cell surface to specific response inside cell

Receptorprotein
Plasmamembrane
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Target cell
Relayproteins
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Transcription factor(activated)
Nucleus
DNA
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Transcription
mRNA
Newprotein
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Translation
Figure 11.14
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Cloning

• A clone is an individual created by asexual
  reproduction and thus is genetically identical to
  a single parent

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Cloning

• Regeneration
• Nuclear Transplantation
• Reproductive and Therapeutic cloning

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Reproductive Cloning

• Clone grown into new individual
• Not exact copy
• Behavioral differences
• Ethical questions

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Therapeutic Cloning

• Medical potential
• Embryonic stem cells
• Adult stem cells
• Replace non-reproducing specialized cells as
  needed
• Only give rise to certain tissues

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Cancer

• Divide uncontrollably
• Mutations whose protein products affect the cell
  cycle
• Oncogene
• Can cause cancer when present in a single copy

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Cancer

• Proto-oncogene
• Gene that has potential to become oncogene
• Mutation or virus

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Cancer

• Tumor-suppressor genes
• Help prevent uncontrolled growth

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• Oncogene proteins and faulty tumor-suppressor
  proteins can interfere with normal signal
  transduction pathways

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Cancer

• Series of genetic changes
• Colon cancer

Colon wall
Cellularchanges
DNAchanges
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Cancer

• Series of mutations

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Videos

• Lac Operon
• http//www.youtube.com/watch?vW6s7I3I0Kh4feature
  related
• http//www.youtube.com/watch?vNfeUT3AUJd0feature
  related
• RNA Splicing
• http//www.youtube.com/watch?v4X8eK15R8yYfeature
  related
• http//www.youtube.com/watch?vFVuAwBGw_pQfeature
  related