Gene Expression

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Gene Expression
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so why does a muscle cell have different
structure and function than a nerve cell?

• Remember, every cell in your body contains the
  exact same DNA

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Review DNA codes for
Proteins!
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Proteins being produced can be turned off and on
just like a light switch based on the needs of a
cell.
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Chromosomes

• A structurally organized single piece of coiled
  DNA containing many different genes. Each gene
  will code for ONE single PROTEIN.

Gene 1
Gene 2
Gene 3
Gene 4
Gene 5
Gene 6
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Regulated Gene Expression

• Regulated control the speed/amount
• Gene Expression using the information from a
  gene to express a protein
• Regulated Gene Expression how a cell controls
  the speed or amount of a gene being expressed as
  a protein

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Methods of regulation

• In Eukaryotes
• Regulating transcription (DNA ? mRNA) by
• Activator Proteins
• Promoters
• 2. Splicing of mRNA
• Exons - Expressed

• In Prokaryotes
• Regulating transcription (DNA ? mRNA) by
• Operators
• Promoters
• Repressor Protein

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Regulation in Eukaryotes1 Regulating
Transcription (DNA ? mRNA)

• If a protein is needed by the cell, a gene coding
  for that protein needs to be expressed,
  TRANSCRIPTION WILL OCCUR.
• If a protein is NOT needed by the cell,
  TRANSCRIPTION WILL STOP.

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Eukaryotic Transcription Factors

• - Activator Protein - a molecule that turns ON
  transcription
• - Transcription Factors molecules that allow
  RNA Polymerase to bind to DNA and begin
  transcription
• - Promoter sequence
• on DNA before the
• Gene where Activator
• Proteins and
• Transcription
• Factors can bind to

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EukaryoticTranscription will TURN ON

• When Activators and Transcription Factors are
  both bound to the Promoter site, RNA polymerase
  will bind to DNA and begin transcription.
• The gene will be transcribed and the protein will
  be translated/expressed.

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Eukaryotic Splicing RNA

• After Transcription Portions of the transcribed
  mRNA is (spliced) cut out
• Exons the portions of the gene on mRNA that are
  cut, translated, and EXPRESS proteins
• Intron the portions of the gene on mRNA that do
  not code for proteins and are NOT expressed
• The spliced Exons will then code for a Protein!

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Regulation of Prokaryotic Genes

• Operon multiple genes that are grouped together
  on one consecutive segment of DNA that is
  transcribed/copied onto ONE single mRNA
• Promoter sequence in an operon where RNA
  polymerase binds to and begins transcription
• Operator sequence in an operon where a
  repressor can bind or unbind to
• Repressor a protein that can bind to the
  operator to PREVENT Transcription from occurring

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Lac Operon - Prokaryotes

• Lac Operon a DNA sequence of three genes (Lac Z,
  Lac Y, Lac A) that codes for proteins that
  break down lactose

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When lactose is present
- Repressor is NOT BOUND to the operator - RNA
polymerase can bind to the PROMOTER and
TRANSCRIPTION OCCURS - Expression of lactase
proteins occurs
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When lactose is absent
Repressor IS BOUND to the operator RNA
polymerase can NOT bind to the PROMOTER and
TRANSCRIPTION Does NOT Occur Expression of
lactase proteins is REPRESSED! (switch is OFF)