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REGULATION of GENE EXPRESSION. GENE EXPRESSION. all cells in one organism contain same DNA every cell has same genotype phenotypes differ skin cells have different structure & function from muscle cells. GENE EXPRESSION. differences -due to differences in gene expression

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gene expression
GENE EXPRESSION
  • all cells in one organism contain same DNA
  • every cell has same genotype
  • phenotypes differ
  • skin cells have different structure & function from muscle cells
gene expression3
GENE EXPRESSION
  • differences -due to differences in gene expression
  • some genes are turned on
  • others are turned off in different cells
  • functionally eliminates particular cell from doing certain functions
  • cell cannot make proteins needed to do certain functions
gene expression4
GENE EXPRESSION
  • expression of most genes is controlled at transcription
  • some genes are actively transcribed
  • others remain quiescent
  • some function at all times
  • 30,000 are expressed in nearly all cell types
  • housekeeping genes
    • carry out basic metabolic processes
  • called constitutive
  • other genes are regulated
    • turned on or off as needed
transcription factors
Transcription Factors
  • proteins which bind to promoter & enhancerregions of DNA to turn on (or off) genes
  • ability to be turned on is inducible
  • ability to be turned off is repressible
  • genes are most often regulated as a group
  • located next to one another on a chromosome
  • these genes along with their regulatory sequences of DNA are called an operon
the lac operon
The Lac Operon
  • E. coli cells
    • use different sugars for energy
    • glucose & lactose
    • ability to use lactose requires special enzymes
    • transacetylase
    • lactose permease
    • beta-galactosidase
  • genes for these enzymes are found on a single unit-operon
the lac operon7
The Lac Operon
  • tells cell machinery to make or not to make enzymes
  • Consists of genes that make enzymes , promoter & operator-control sequences
  • promoter region
    • transcription enzyme-RNA polymerase attaches
    • begins transcription
  • operator
    • functions as switch
    • determines if RNA polymerase can attach to promoter region
lac operon
Lac Operon
  • transcription of 3 enzymes is repressed-turned off by repressor protein
    • binds to operator
    • blocks attachment of RNA polymerase
    • regulatory gene located outside operon codes for repressor
  • regulatory gene is expressed all the time
  • if regulatory gene is always being transcribed
  • there is always repressor protein to stop transcription of enzymes needed to use lactose
  • How is lacoperon turned on?
  • lactosein environment
lac operon9
Lac Operon
  • lactose binds to repressor protein changes its shape.
  • new shape means it cannot bind to active site of operatorsite is turned on
  • RNA polymerase attaches
  • transcription of enzymes needed to metabolize lactose begins
  • genes that code for enzymes that lets cell use lactose are made only when lactose is present
  • induction
    • presence of a small molecule causes enzymes to be made
trp operon
trpoperon
  • bacteria
  • repressor-inactive alone
  • to be active combines with specific small molecule
  • that small molecule is amino acid- tryptophan
  • E. coli can make tryptophan using enzymes in trp operon but if tryptophan do not make their own
  • tryptophan binds to repressor
  • activates repressor
  • turns off operon
  • when tryptophan is not present repressor is not active operon is turned ontryptophan is made
repressor operon
Repressor Operon
  • arginine is an essential amino acid
  • when plentifule. coli cellsuse it
  • arginine not presente. coli must make it
  • requires enzymes
  • mechanism allows e. coli cells to save cellular resources by shutting genes off for particular substance when substance is available
gene regulation in eukaryotes
Gene Regulation in Eukaryotes
  • cells differ in appearance & function
  • inherit same, complete set of genetic information
  • differences in appearance & function is not due to different genes
  • differences due to genes being turned on or off
  • cells performing particular functions are termed specialized
  • during development cells differentiate & stay differentiated
  • terminally differentiated
gene expression eukaryotes
Gene Expression-Eukaryotes
  • begins at chromosome level
  • DNA in one chromosome is about 4 cm long
  • entire amount can fit into nucleus because of way it is packaged
dna packaging
DNA PACKAGING
  • DNA helix is wound around small proteins- histones
  • DNA-histone complex looks like beads on a string
  • each bead-nucleosome
  • segment of DNA wound around 8 histones
  • short DNA segments-linkers make up string part between nucleosomes
dna packaging17
DNA PACKAGING
  • beaded strings are wrapped into tight helical fibers
  • which in turn are coiled into supercoils
  • looping & folding further compacts DNA
dna packaging18
DNA PACKAGING
  • extreme packaging is important in gene regulation
  • prevents gene expression by preventing transcription proteins from contacting DNA
  • some regions-heterochromatin
  • so condensed-never transcribed
    • 10% of genome
  • remainder of complex- euchromatin
  • less condensed
  • can be transcribed
  • 10% is active at any given time
fine control of transcription in eukaryotic cells
Fine Control of Transcription in Eukaryotic Cells
  • fine tuning is done with control of RNA synthesis-transcription
  • most important way of regulating gene expression
control of transcription in eukaryotic cells
Control of Transcription in Eukaryotic Cells
  • regulatory proteins bind to DNA to turn transcription of genes on & off
  • each eukaryotic gene has its own promoter & other control sequences
  • Activator proteins are more important in eukaryotic cells than in prokaryotic cells
  • in most eukaryotic organisms genes are turned off
  • small percentage of genes must be turned on for any one particular cell to make proteins required to carry out its particular job
control of transcription in eukaryotic cells21
Control of Transcription in Eukaryotic Cells
  • regulatory proteins in eukaryotic cells are transcription factors
  • required for RNA polymerase to transcribe DNA
control of transcription in eukaryotic cells22
Control of Transcription in Eukaryotic Cells
  • first step in gene transcription is binding of transcription factors to DNA sequences-enhancers
    • usually far away from genes they regulate
  • binding of activators to enhancers causes DNA to change shape
  • it bends
  • with bending bound activators can interact with transcription factor proteins which act as a complex at promoter area of gene
  • this complex promotes attachment of RNA polymerase to promoter transcription begins
  • there are also repressor proteins- silencers
  • inhibit transcription
splicing regulation
Splicing & Regulation
  • transcription of DNA  mRNA
  • used to make a specific protein by translation
  • mRNA can be regulated by splicing
splicing regulation24
Splicing & Regulation
  • during splicing certain segments of RNA are eliminated
  • the way a piece of mRNA is spliced giving rise to different types of mRNA
  • gives rise to different proteins
regulation of translation
Regulation of Translation
  • after mRNA has been fully processed and is in the cytoplasm other regulatory processes may occur
  • mRNA breakdown
  • initiation of translation
  • protein activation
  • protein breakdown
mrna breakdown
mRNA Breakdown
  • mRNA molecules do not stay intact forever
  • broken down by enzymes
  • time of breakdown is important
  • regulates amount of protein that is made
  • longer living mRNAs can make more protein
initiation of translation
Initiation of Translation
  • many proteins control initiation of translation of RNA
  • in red blood cells, translation does not occur unless heme is present
protein activation
Protein Activation
  • after translation is complete proteins often need altering to become functional
  • many made as proenzyme
  • Inactive
  • cleaving part of protein makes it functional
protein breakdown
Protein Breakdown
  • proteins can be broken down after a short or after a long time
  • broken down after short timehave limited time to carry out functions
  • may be important in short term regulatory activity in cells
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