Transcription Circuits Flashcards
What is the transcriptome?
The segment that is transcribed
Summarise the different types of transcript(3)
- Abundant transcript- If on in every cell this is called a HOUSEKEEPING gene (e.g. glycolytic enzymes). Essential for cell function eg RNA Pol II
- Rare Transcript- Inducible gene. When given hormone it transcribes.
- No transcript- Tissue specific eg globin. Expressed in one type but not in another.
What is the role of promotors?
· The sequence immediately 5’ to the region to be transcribed is called a “promoter”
• Promoters recruit RNA polymerase to a DNA template
How is recognition of promotors mediated in prokaryotes and eukaryotes?
– Predominantly “Sigma factor” for prokaryotes
– The TFII basal transcriptional machinery for eukaryotes
What are the prokaryotic promotors?
· Sigma factor recognises the -35 and -10 motifs common to prokaryotic promoters and enables RNA polymerase to make stable contacts with DNA
What are alternative names for the -10 and -35 regions?(2)
10 region is the Pribnow region -35- consensus sequence- most likely to find
What are the eukaryotic promotors?
1.TATA box need to recruit general transcription factors and then RNA polymerase. It is the consensus region for recognition2. TATA binding factor= TBP
What are regulatory transcriptition factors?(3)
- In both prokaryotes and eukaryotes they function to dramatically alter the level of recruitment of RNA polymerase and/or its ability to initiate transcription
- in eukaryotes they can influence local chromatin structure
- They do not have to unwind the DNA double helix to see their target so an intact DNA molecule can present info to the cell.
What is lac operon in prokaryotes?
Lac Operon codes for three genes- ZYA- required for using lactose for source of energy. Promotor responds to the presence of lactose
Describe the state of lac ZYA in the presence of glucose and no lactose(2)
- In the presence of glucose and lactose they will promote use of glucose. More energy can be made from glucose
- No transcription of thelacoperon occurs because thelacrepressor remains bound to the operator and prevents transcription by RNA polymerase
Describe the state of lac ZYA in the presence of lactose and no glucose(2)
Strong transcription of thelacoperon occurs.1. Thelacrepressor is released from the operator.
CAP( Catabolite activator protein ) is active and bound to the DNA.
- CAP helps RNA polymerase bind to the promoter, permitting high levels of transcription
Name some eukaryotic triggers of transcription switches
Immune stress, cAMP, Oestrogen
Describe how hormones interact with promotor regions (6)
- The cytoplasm contains receptors for the hormone.
2 .Steroid hormone bind to receptor protein
- A change in the shape of protein.
- The protein translocate to the cytoplasm.
- In the nucleus, the protein scans and bind to the promotor region.
- Recruits binding factors and transcription occurs.”
What is GATA-1?
– GATA-1 are tissue specific factor- only expressed in RBCs- it binds to promotor region to recruit RNA polymerase II
What happens when RBCs differentiate to start expression of B-globin?
– As RBCs differentiate- NF1, CP1, Sp1 are ubiquitous factors- they start producing the expression of B globin.
How are transitions through the cell cycle regulated?(5)
- The promoters for G1/S transition genes are activated by a factor called E2F. Acts as dimers and bind to specific DNA sequence.
- E2F activity is repressed in G0 and early G1 by the product of the Retinoblastoma gene (pRB)
- E2F binds to DNA but cant recruit RNA polymerase because pRb is attached to them
- When mitogenic stimulus is added pRb are phosphorylated and their shapes change and unbind from E2F.
The transitions to the different phases are regulated by cyclins and CDKs.
What does mutations in pRB mean and what is the role of viral oncogenes in cancers?(2)
- Mutations mean lack of pRB so cells are always activated.
- Viral oncogenes express proteins that compete for binding of the pRb so cells are constantly transcribed because E2F is free.
What are enhancers?(3)
→They are sequences of DNA (not immediately adjacent to where transcription starts)
→act to enhance the recruitment of RNA polymerase to a promoter.
→They can reside in the 5’, 3’ or even the introns. They are very strong binding sites for specificity factors.
The recognition of promoters is mediated by initiation factors. What are these factors in prokaryotes?
→It is the sigma factor, which recognises the -35 and -10 motifs common to prokaryotic promoters.
The recognition of promoters is mediated by initiation factors.
What are these factors in eukaryotes?
It is the TF2 basal transcriptional machinery (TF2A, TF2B, etc.).
List the known transcriptional switch in prokaryotes (1) and eukaryotes (3).
→PROKARYOTES: - the lac operon
→EUKARYOTES: - oestrogen-responsive transcription - tissue-specific translation (beta-globin) - a complex regulatory circuit (cell cycle)
how does the lac operon work?(5)
E.coli prefer using glucose as an energy source, but when glucose is absent they can use lactose instead.
→The Lac Z gene codes for an enzyme that cleaves the lactose into simpler sugars.
→Lac Y codes an enzyme that is used for the absorption of lactose.
→When there is no lactose available then the cell will not transcribe the Lac genes because it is energetically expensive.
The lac repressor protein binds to the promoter region before the start site, the RNA polymerase will not be able to transcribe the genes as the repressor is blocking the RNA from moving forward.
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what are inducible genes?
genes which are transcribed in response to stimuli.
what do position and orientation independent mean?
→Position independent means that the enhancer can be cut out and be put in another place and it will still work.
→orientation independent so the enhancer can be reinserted backwards and it will still function properly.
