Docstoc

regulation

Document Sample
regulation Powered By Docstoc
					Gene Regulation
Thinking about Gene Regulation
 Humans begin life from a single cell,
  therefore all the genetic information needed
  to create a human is in our genome
 Embryonic cells undergo differentiation to
  produce specific cell types such as muscle,
  nerve, and blood cells
 Different cell types are the consequence of
  differential gene expression
    Thinking about Gene Regulation
 A typical differentiated mammalian cell
  makes about 10,000 proteins from
  approximately 35,000 genes
 Most of these are housekeeping proteins
  needed to maintain all cell types
 Certain proteins can only be detected in
  specific cell types
 How is gene expression regulated?
Regulation of Gene Expression

 Transcriptional control
 RNA processing control
 Translation control
 Protein activity control
Regulation of Gene Expression
                     Gene Organization
     Prokaryotic:
5’                                                           3’
        Promoter       Gene 1       Gene 2     Gene 3
3’                                                           5’




     Eukaryotic:
5’                                                            3’
        Promoter    Exon 1 Intron 1 Exon 2 Intron 2 Exon 3
3’                                                            5’
    Transcriptional Control
 Genes have regulatory DNA sequences
  upstream from the initiate site where
  transcription begins
 The promoter is the RNA polymerase
  binding site
 Gene regulatory proteins bind to regulatory
  DNA sequences and can either prevent or
  enhance RNA polymerase binding
Gene Regulatory Proteins Bind to DNA
DNA-binding motifs in proteins

  In the homeodomain,
  three alpha helices
  interact with the DNA.
DNA-binding motifs

  The zinc-finger motif is
  composed of an alpha
  helix and a beta sheet.

  Each zinc-finger is held
  together by a molecule
  of zinc
DNA-binding motifs

  In the leucine zipper
  motif, two alpha helices
  interact with the DNA.

  The two alpha helices
  are from different
  proteins.
Repressor Proteins

 Repressor proteins bind to an operator site
  within the promoter.
 Binding of a repressor prevents binding of
  RNA polymerase
 The repressor is an allosteric protein that
  can be activated by binding to a small
  molecule
Regulation of tryptophan synthesis
Activator Proteins

 Activator proteins bind to DNA sequences
  and then interact with RNA polymerase to
  enhance its binding
 Activator proteins can be allosteric and bind
  to small molecules before they can bind to
  DNA
Activator Proteins
Regulation of Eukaryotic Gene Expression

    General transcription factors are needed
     to initiate transcription
    Regulatory sequences: thousands of
     nucleotides from the promoter can influence
     transcription
Highly methylated regions of DNA
correspond to inactive genes.
     promoter region                          coding region

enhancer TATA                      exon 1 intron 1 exon 2 term seq


               general
         transcription factors
activating
 factors  TBP
                          RNA
 enhancer TATA            Pol II   exon 1 intron 1 exon 2 term seq


                general
         transcription factors
 activating
  factors  TBP
                                                RNA
 enhancer TATA                                       exon 2 term seq
                                    exon 1 intron 1 II
                                                Pol


                                      hnRNA
                                                              Eukaryotic
      Regulation of Gene Expression by Upstream Elements



Prokaryotes
Operon (Lac, Trp):several genes controlled by single regulator
             operator-sequence to which repressor protein binds
             repressor-when bound inhibits transcription
             regulator gene-codes for repressor


Eukaryotes
Each gene with its own promoter region

Binding sites for basal transcription factors as well as sequence
specific binding proteins that activate or inhibit transcription

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:3
posted:11/9/2012
language:English
pages:21