CONTROL OF TRANSCRIPTION Flashcards
transcription
making RNA from DNA
Translation
making protein from RNA, needs RNA (rRNA/mRNA)
what was originally considered origin of life?
RNA; as it can carry information and carry out functions. But RNA is not a stable store of information. DNA is more stable storage of information.
why is RNA important?
needed for information, as an intermediate, structure and function.
describe RNA polymerase
- large (500kD)
- complex sub-unit composition
- dynamic molecular motor
- polymerisation and nucleolysis
- ultimate target of all transcription regulation
- rigid and flexible dynamic structures crucial for functions such as RNA polymerase clamping down on DNA
what is the directionality of transcription?
5’ to 3’ on RNA transcript, works on the 3’ to 5’ on DNA template strand
where does RNAP bind in transcription?
the promoter region
what is the template strand? what is coding strand?
template = strand that produces mRNA sequence.
coding = strand that corresponds to the mRNA
where does transcription and translation occur in prokaryotes?
in the cytosol; as they have no nuclear membranes. the processes are coupled.
what do ‘housekeeping genes’ do?
in prokaryotes some proteins are expressed constant amount - this is regulated by housekeeping genes.
what is an operon?
cluster of genes under control of the same promoter.
promoter sequence = where RNApol binds
operator sequence = where repressor binds and inhibits RNAP binding
structural sequence = sequence which codes for proteins
explain the lac operon
lactose –> galactose + glucose.
- inducible operon
- transcription increases if concentration of lactose increases.
- without lactose, lac operon is repressed; repressor is bound to operator region preventing RNAPol binding therefore no transcription.
- lactose present; lactose binds to the repressor and causes it to change shape; prevents repressor binding to operator so transcription can occur
how is transcription different in eukaryotes?
- transcription is compartmentalised
- the enhancers and silencers / regulation of transcription is not same as in prokaryotes; not found in promoter region but kilo bases upstream of transcription start site on same / different chromosome.
describe the mechanism of transcription?
- initiation: transcription factors bring RNA pol to the promoter; binds to 5’ end.
- elongation: mRNA is synthesised from antiparallel template strand if the required transcription factors and NTPs are present. the mRNA transcript is = to the coding strand with exception of uracil.
- termination: RNA pol reaches stop signal and detaches, and restarts to make multiple copies of one gene.
how is transcription controlled in eukaryotes?
RNA pol cannot bind directly to promoter without transcription factors being present; 3 step process.
- sequential assembly of transcription factors (TFIID, TFIIB and TFIIA) which bind to the TATA box within promoter
- then there is recruitment of RNA pol II and further transcription factors (TFIIF, TFIIE and TFIIH) to form transcription initiation complex
- presence of NTPs allows transcription to occur.
what happens after DNA –> RNA transcript?
- ‘cap’ is added (7 methyl guanosine) to the 5’ end
- transcript is spliced by splicosome, to remove introns, and produce mRNA. introns loop out and axons join.
- polyadenylation: a polyA tain is added to 3’ end
what is the role of 7-methyl guanosine?
cap for the RNA transcript which increases stability and prevents degradation
what is the importance of poly adenylation?
important for translation and stability of mRNA. it degrades over time, and when short enough, mRNA is enzymatically degraded.
what is the consequence of splicing mutations?
diseases such as beta thalassemia; one of bases is mutated from G to A so one intron cannot be removed.
how could hormones control transcription?
steroid hormones may interact with nuclear membrane receptors and alter gene expression.
protein hormones may bind to plasma membrane receptors = signalling cascade.
