Transcriptional circuits in prokaryotes and eukaryotes Flashcards
What is the transcriptome
The genes that are actually transcribed, around 50% of prokaryotic genes
What is an abundant transcript
House keeping genes e.g. RNA polymerase II, glycolytic enzymes
why are some genes not translated
Tissue specific genes eg. Globin which is only expressed in red blood cells
what is an Inducible transcript
When a rare or no transcript gene is made into an abundant transcript after response to a stimulus
Where is the promoter region and what does it do
A DNA sequence that lies immediately 5’ to the transcribed region that recruits RNA polymerase II to a DNA template
Where are enhancers situated
Upstream or downstream to transcription unit or even located within an intron
They can be moved and reversed without changing its effect
What does an enhancer do and how does it work
A DNA sequence that enhances the recruitment of RNA polymerase to a promoter
They contain very strong binding sites for specificity factors or transcription factors
What is required for RNA polymerase to bind and why
Initiation factors are required for the binding of RNA polymerase since it slides along the duplex without being able to recognise promoters
What is the prokaryotic initiation factor
Sigma factor
What is the eukaryotic initiation factor
TFII basal transcriptional machinery
Lac operon - Glucose present, lactose absent
- Lac repressor remains bound to the operator
- cAMP levels are low since glucose levels are high so CAP protein is inactive and cannot bind to DNA
- Lac ZYA genes not expressed
Lac operon - Glucose present, lactose present
- Lac repressor is unbound from the operator
- cAMP levels are low since glucose levels are high so CAP protein is inactive and cannot bind to DNA
- Lac ZYA genes expressed at low levels
Lac operon - Glucose absent, lactose absent
- Lac repressor remains bound to the operator
- cAMP levels are high since glucose levels are low so CAP protein will be bound to DNA
- Lac ZYA genes not expressed
Lac operon - Glucose absent, lactose present
- Lac repressor is unbound from the operator
- cAMP levels are high since glucose levels are low so CAP protein will be bound to DNA
- Lac ZYA genes highly expressed
Steroid hormone signalling process
- Steroids will cross membranes and bind to recognition proteins in the cytoplasm
- This changes the proteins shape so it can translocate into the cells nucleus
- The complex will bind to the promoter region that has that specific DNA binding sequence
- It will activate transcription of those genes
Why is oestrogen artificially regulated and how
- Tamoxifen competes for binding with oestrogen recognition proteins
- The tamoxifen complex cannot recruit RNA polymerase II therefore the oestrogen growth factor genes are not made
- This helps in reducing the growth of breast cancer
Transcriptional activation of genes for the regulation
of the cell cycle
- mitogenic stimulus will activate CDKs
- CDKs will phosphorylate retinoblastoma protein (pRB)
- pRB wont be able to bind to E2F
- E2F can now bind to E2F sites and activate the expression of the gene that codes for proteins involved in DNA replication
- Cell cycle transitions from the G1 to S phase
What effect does cancer have on pRB
- pRB isn’t made
- E2F is always bound to the promotor
- The cell cycle isn’t regulated and the cell divides uncontrollably
