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20 Cards in this Set

  • Front
  • Back
Regulation of Gene Expression
control of transcription
Methods of regulation of Gene Expression
Info transfer

Repression blocks transcription

Induction initiates transcription of gene
Info transfer method
DNA--> RNA--> Protein
How does repression regulate methods of gene expression?
Co-repressor is usually the end product of a synthetic pathway – called feedback repression
b. Repressor is the regulatory protein that blocks transcription of genes that code for protein synthesis (ex: enzymes are not formed) OP (Fig 8.13)
c. Contrast with enzyme inhibition = control of existing enzymes
i. feedback inhibition controls existing
How does induction initiate transcription of genes?
Induction initiates transcription of gene
a. Inducer is substance that acts to start transcription
b. Often = catabolite (ex: lactose)
Lactose Operon Model for Induction Control discovered
after study of ________.
lactose genes in E. coli
All ___________ contain all the genes to produce all enzyme products
wild type E. coli
True or False:
Most genes are turned off & produce protein products only when needed (true of eukaryotes as well)
What does Beta galactosidase (Z) do?
Metabolizes lactose, breaks it down into glucose and galactose
What does β galactoside permease (Y) do?
Transports lactose into cell
thiogalactoside transacetylase (A) does what
metabolizes other disaccharides
Components of the Operon (there's 2)
a. Structural genes, which code for the 3 lactose enzymes (Z, Y, A)

b. Control region made up of 2 sites
Function & Location of structural genes, which code for the 3 lactose enzymes (Z, Y, A)
i. these genes specify a.a. sequence of protein

ii. these genes are (physically) located next to each other
What are the two sites the Control region is made up of?
i. Operator (O) – on/off switch
ii. Promotor (P) – (next to operator) where RNA polymerase binds to initiate transcription (in eukaryotes = TATABOX)
True or false:

Regulator gene never makes repressor protein.
False! It always (24/7) makes the repressor gene
in absence of inducer allolactose (lac –allolactose), what happens?
i. repressor protein is active & binds to operator (turning it off)
ii. promotor is blocked so RNA polymerase cannot synth RNA
iii. (therefore) no transcription of lac(tose structural) genes
in presence of inducer allolactose, what happens?
i. repressor protein is inactivated
ii. the operator is turned on
iii. RNA polymerase can transcribe the lac(tose) structural genes for translation into the 3 lac(tose) enzymes
iv. allolactose actually induces (stimulates) synthesis of lactose digesting enzymes
2 types of enzymes
inducible enzyme
constitutive enzymes
inducible enzyme
synthesis is initiated by catabolite inducer
constitutive enzymes
synthesized all the time & not subject to control (ex. pathways with enzymes always produced = glycolysis & Krebs cycle)