Transcriptional circuits

Question 1

What type of genes have abundant transcripts? [1 mark]

Answer 1

Housekeeping genes (e.g. glycolytic enzymes)

Question 2

What type of genes have rare transcripts? [1 mark]

Answer 2

Genes that need a stimulus to be transcribed (i.e. inducible genes).

Question 3

What type of genes have no transcripts? [2 marks]

Answer 3

• Tissue specific genes (e.g. globin)

- Inducible genes.

Question 4

What is the promoter and what does it do? [1 mark]

Answer 4

• The sequence immediately 5’ to the transcriptome.

- It recruits RNA polymerase to a DNA template.

Question 5

What is the enhancer and what does it do? [1 mark]

Answer 5

• A sequence of DNA not immediately adjacent to the transcriptome (either at 5’ or 3’).
• It enhances recruitment of RNA polymerase to a promoter.

Question 6

What are the initiation factors in prokaryotes and eukaryotes? [2 marks]

Answer 6

PROKARYOTE: Sigma factor
EUKARYOTE: TFII basal transcriptional machinery

Question 7

Where is the initiation site in prokaryotes? [1 mark]

Answer 7

+1

Question 8

Where is the Pribnow box (TATAAT) and what is it needed for? [2 marks]

Answer 8

• At position -10

- Important part of the promoter site in bacteria.

Question 9

What is at position -35 in prokaryotes? [1 mark]

Answer 9

TTGACA

Question 10

What does the sigma factor recognise? [2 marks]

Answer 10

• Motif at -10

- Motif at -35

Question 11

What does the TATA box do? [1 mark]

Answer 11

Recruits general transcription factors and RNA polymerase.

Question 12

What does TFIIA do? [1 mark]

Answer 12

Stabilises the pre-initiation complex.

Question 13

What does TFIIB do? [2 marks]

Answer 13

• Interacts with TBP subunit of TFIID.

- Recruits RNA polymerase II

Question 14

What does TFIID do? [1 mark]

Answer 14

Recognises the initiation complex and binds to it.

Question 15

What does TFIIE do? [1 mark]

Answer 15

Binds to TFIIH.

Question 16

What does TFIIH do?

Answer 16

Binds to TFIIE.

Question 17

What does CAP do in the LAc Operon? [1 mark]

Answer 17

• Binds to the promoter sequence.

- Induces expression of the ZYA genes.

Question 18

Where does oestrogen bind to once it crosses the phospholipid bilayer of the target cell? [3 marks]

Answer 18

• Binds to the oestrogen receptor protein in the cytoplasm.
• Oestrogen-receptor complex enters the nucleus and scans for the right gene.
• The gene has an oestrogen responsive element and binding to this causes the recruitment of transcription factors.

Question 19

Where is GATA-1 located and what is it? [2 marks]

Answer 19

• At the enhancer region of erythroblasts

- It’s a transcription factor

Question 20

What does oestrogen do in breast cancer? [3 marks]

Answer 20

• Increases proliferation of the cancer cells
• Increases mutation rates
• Induces aneuploidy

Question 21

What does Tamoxifen do to treat breast cancer? [2 marks]

Answer 21

• Its an antagonist of oestrogen.

- It has a different shape so RNA polyermase can’t be recruited

Question 22

What do Cdks do? [1 mark]

Answer 22

• Phosphorylate the transcription factors.

- They become active when bound to cyclins.

Question 23

What do cyclins do? [1 mark]

Answer 23

Regulate Cdks.

Question 24

What does E2F do? [4 marks]

Answer 24

Helps transcribe genes for:

• DNA polymerase
• Thymidine kinase (increases thymidine content in cells)
• DHFR
• ribonucleotide reductase etc.

Question 25

When is E2F activity repressed? [2 marks]

Answer 25

• At G0 and G1

- By the retinoblastoma protein (pRB) [UNPHOSPHORYLATED FORM]

Question 26

How can viral oncogene prevent pRB from binding to E2F? [2 marks]

Answer 26

• Competes for beining with pRB

- This happens in HPV, Hep B and C etc.