Transcriptional Circuits In Prokaryotes And Eukaryotes

Question 1

What is a transcriptome?

Answer 1

The segment of the genome that is transcribed

Question 2

How much of the transcriptome is transcribed at one time?

Answer 2

A fraction

Question 3

What are the three levels genes can be transcribed at?

Answer 3

1 (abundant)
2 (rare)
3(no transcription)

Question 4

Inducible genes

Answer 4

Genes that aren’t expressed or are hardly expressed at all react to a stimuli and are them transcribed abundantly

Question 5

What is recognition of promoters mediated by?

Answer 5

Initiation factors

Question 6

What are the initiation factors in prokaryotes and eukaryotes

Answer 6

Sigma factor (prokaryotes)
TF11 basal transcription machinery (eukaryotes)

Question 7

Once stably recruited to DNA, what is able to convert DNA from a closed to an open complex

Answer 7

RNA polymerase

Question 8

What’s a consensus sequence?

Answer 8

A sequence you are most likely to find if you were working on a base sequence

Question 9

What do sigma factors recognise that enables RNA promoters to make stable contacts with DNA

Answer 9

-35 and -10 motifs

Question 10

What is the sigma factor in eukaryotes

Answer 10

TATA box binding factor (TBP)

Question 11

Why is a TATA box needed?

Answer 11

Needed to recruit general transcription factors and then RNA polymerase

Question 12

What are regulatory transcription factors?

Answer 12

They mediate regulatory charges

Question 13

What do regulatory transcription factors do in both prokaryotes and eukaryotes?

Answer 13

They function to dramatically alter the level of recruitment of RNA polymerase and/or its ability to initiate transcription

Question 14

What can regulatory transcription factors do only in eukaryotes?

Answer 14

They can influence local chromatin

Question 15

What is the lac operon

Answer 15

A prokaryotic paradigm for the regulation of transcription

Question 16

Do regulatory transcription factors have to unwind the DNA double helix to see their target?

Answer 16

No, so an intact DNA molecule can present info to the cell

Question 17

What is the transcriptional switch in prokaryotic cells?

Answer 17

The lac operon

Question 18

What are the transcriptional switches in eukaryotic cells?

Answer 18

Oestrogen-responsive transcription
Tissue specific transcription (beta globin)
A complex regulatory circuit (cell cycle)

Question 19

What do bacteria prefer to use as an energy source rather than lactose and why?

Answer 19

Glucose as it provides more energy for ATP

Question 20

How is the lac gene switched off in bacteria if glucose is present?

Answer 20

The CAP protein is only active under low glucose conc. if there is no lactose present, the lac repressor binds to the DNA in the promoter region

Question 21

What is the transcription factor if immune stress is the trigger?

Answer 21

NF-KB

Question 22

What is the transcription factor if cyclic AMP is the trigger?

Answer 22

CREB

Question 23

What is the transcription factor if oestrogen is the trigger?

Answer 23

Oestrogen receptor

Question 24

What is the transcription factor if interferon is the trigger?

Answer 24

ISGF3

Question 25

Give the steps for steroid hormone signalling

Answer 25

Steroid ->receptor protein -> hormone -> receptor complex -> transcription/mRNA -> New protein

Question 26

Give one way therapeutic drugs can be targeted

Answer 26

Interfering with the interactions between regulatory and general transcription factors

Question 27

What is tamoxifen and what is it used for?

Answer 27

A competitive inhibitor for oestrogen so it means that the oestrogen-responsive translation can’t take place. Used as a cancer treatment

Question 28

How does tissue-specific transcription (beta globin) take place?

Answer 28

As the cell differentiates, the ubiquitous factors start expressing their gene and over time, the tissue-specific factor becomes more common

Question 29

How is the cell cycle regulated?

Answer 29

The promoters for G1s transition genes are activated by a factor called E2F

Question 30

Give the steps of cell cycle regulation

Answer 30

E2F activity is repressed in G0 and early G1 by the product of the retinoblastoma gene (pRB).
If the pRB is phosphorylated, then it can no longer bind to the E2F and it can then translate the gene.