gene control Flashcards
constitutive vs inducible genes
cons = transcribed at all times
induc = only transcribed under centrain conditions
what is he role of the lac operon
contains genes that code protens for break down of lactose
what proteins/enzymes does lac operon form and what genes are responsible
lacZ = beta=galactosidase
lacY = permease
lacA = transcetylase
lacI = repressor proteins (regulatory gene)
role of each enzyme/protein n lac operon
b-gal - breaksdown/cleave lactose into its two monosaccharides (galactose and glucose)
permease = allows lactose into cell (permeability)
trans = transfers CoA to lactose
repressor = binds to operon and stops polymerase binding
what is isoprpylthiogalactoside (IPTG)
a gratuitous inducer
- not metabolised
how was beta galacotsidase measured in lab 4
- ONPG added to mixture, reacts with B-gal to form ONP which is directly proportional to B-gal, ONP is yellow so measured absorbance at 420nm
what happens when no lactose or glucose is added
- no change
- repressor is able to bind to operator site so that RNA polymerase doesn’t bind and no transcription occurs
- cAMP- CAP complex forms but still doesnt work
what happens when lactose is added?
- cAMP-CAP complex forms and polymerase is able to bind
- repressor protein is inactivated so will not block operator region and RNA polymerase binds
Explain cAMP-CAP complex
in absence of glucose, ATP can become cAMP (catalysed by adenylcyclase).
- cAMP binds to CAP, forms CAP-cAMP complex, this complex bidns to CAP recognitions site near promotor region
- RNA more readily binds to promotor
- if glucose is present, ATP is used in glycolysis processes and adynyl cyclase is inhibited - catabolite repression
Explainwhat happens when glucose is introduced with lactose
- glucose becomes primary carbon source of energy
- lactose will inacivate repressor
- however glucose inhiibits adynyl cyclase so cAMP cannot form and RNA pol can’t find promotor region
- very minimal transcription
what does chlormaphenicol do
- binds to and inhibits the 50S subunit of ribosome so translation cannot occur and proteins are not made
What does sodium azide do
- antibiotic
- kills the cells
what is lactose
a disaccharide that is composed on two monosaccharides, galactose and glucose
what is a regulatory gene
- encodes a protein that regulates gene expression
what is a structural gene
- encodes protein that is not a regulatory gene
what is the promotor region
where RNA polymerase binds
what is the operator
regulatory protein binding site (repressor)
what neg regulation occurs in lac operon? what pos reg occurs?
neg = lac repressor
pos = catabolite activator protein (CAP)
what are the 5 stages of eukaryotic gene regulation WILL be in exam
- genomic - changes in codensation of chromatin for transcription
- transcriptional - enhancers and silencers of genes activated
- post-transcriptional - RNA splicing removes introns
- translational - binding of translational repressors to alter which mRNA genes are translated
- post-translational - phosphylation or dephosphorylation (of proteins)
