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Gene Expression

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Overview. Prokaryotes have operons. Eukaryotes . Regulatory sequences. Selective transcription. Homeobox Genes (HOX) Epigenome – PowerPoint PPT presentation

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Title: Gene Expression


1
Gene Expression
2
Problem
  • All the DNA in an organisms cells is basically
    the same.
  • We have many of the same genes as a fruit fly
    (abt 60).
  • What accounts for the differentiation in the
    cells?

3
  • Which genes are expressed.

4
Overview
  • Prokaryotes have operons
  • Eukaryotes
  • Regulatory sequences
  • Selective transcription
  • Homeobox Genes (HOX)
  • Epigenome

5
PROKARYOTE OPERON
  • Promotor- Where RNA polymerase attaches
  • Operator- switch that turns on or off. If
    repressor attaches, it is off. Transcription is
    disabled.
  • Gene
  • Examples
  • Lac Operon- If Lactose is present, gene turned
    on.
  • Tryp Operon - If Tryptophan is present, gene
    turned off.

6
EUKARYOTE REGULATORY SEQUENCES
  • Proteins can bind to enhancer sequences on gene.
    Depending upon cellular conditions, this may
    enable gene to turn on. Eukaryotes have multiple
    switches.
  • Induction- If proteins from neighboring cells are
    present, gene may turn on (ex retina)
  • Hormones and other molecules may attach to
    enhancer sequence to turn on genes.

7
SELECTIVE TRANSCRIPTION
  • During transcription, intervening sequences of
    mRNA are removed (introns).
  • Exons are spliced together.
  • Males and females have the same set of genes, the
    fact that they are spliced differently accounts
    for the difference in gender.
  • Splicing DNA rearrangement account for millions
    of different antibodies from the same genes.

8
(No Transcript)
9
HOMEOBOX GENES
  • HOX genes
  • Master control genes
  • Segmented organisms have HOX genes associated
    with genes for body parts. For example, since the
    same gene forms antenna and leg, which forms
    depends upon its master control gene.

10
Normal Head
Mutant Head
11
EPIGENOME
  • Environmental effects can impact gene expression.
  • Methylation seems to prevent genes from loosening
    from histones, repressing transcription.
  • Twins can have different diseases, and their gene
    expression becomes more divergent as they age.

12
  • See HMMI Click and Learn Genetic Switches
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