Transcriptional circuits in prokaryotes and eukaryotes

Question 1

What is the transcriptome

Answer 1

The genes that are actually transcribed, around 50% of prokaryotic genes

Question 2

What is an abundant transcript

Answer 2

House keeping genes e.g. RNA polymerase II, glycolytic enzymes

Question 3

why are some genes not translated

Answer 3

Tissue specific genes eg. Globin which is only expressed in red blood cells

Question 4

what is an Inducible transcript

Answer 4

When a rare or no transcript gene is made into an abundant transcript after response to a stimulus

Question 5

Where is the promoter region and what does it do

Answer 5

A DNA sequence that lies immediately 5’ to the transcribed region that recruits RNA polymerase II to a DNA template

Question 6

Where are enhancers situated

Answer 6

Upstream or downstream to transcription unit or even located within an intron
They can be moved and reversed without changing its effect

Question 7

What does an enhancer do and how does it work

Answer 7

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

Question 8

What is required for RNA polymerase to bind and why

Answer 8

Initiation factors are required for the binding of RNA polymerase since it slides along the duplex without being able to recognise promoters

Question 9

What is the prokaryotic initiation factor

Answer 9

Sigma factor

Question 10

What is the eukaryotic initiation factor

Answer 10

TFII basal transcriptional machinery

Question 11

Lac operon - Glucose present, lactose absent

Answer 11

• 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

Question 12

Lac operon - Glucose present, lactose present

Answer 12

• 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

Question 13

Lac operon - Glucose absent, lactose absent

Answer 13

• 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

Question 14

Lac operon - Glucose absent, lactose present

Answer 14

• 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

Question 15

Steroid hormone signalling process

Answer 15

1. Steroids will cross membranes and bind to recognition proteins in the cytoplasm
2. This changes the proteins shape so it can translocate into the cells nucleus
3. The complex will bind to the promoter region that has that specific DNA binding sequence
4. It will activate transcription of those genes

Question 16

Why is oestrogen artificially regulated and how

Answer 16

• 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

Question 17

Transcriptional activation of genes for the regulation

of the cell cycle

Answer 17

1. mitogenic stimulus will activate CDKs
2. CDKs will phosphorylate retinoblastoma protein (pRB)
3. pRB wont be able to bind to E2F
4. E2F can now bind to E2F sites and activate the expression of the gene that codes for proteins involved in DNA replication
5. Cell cycle transitions from the G1 to S phase

Question 18

What effect does cancer have on pRB

Answer 18

1. pRB isn’t made
2. E2F is always bound to the promotor
3. The cell cycle isn’t regulated and the cell divides uncontrollably