Transcriptional Circuits

Question 1

What is the rate of transcription of the transcriptome?

Answer 1

Only a fraction of the transcriptome is transcribed at any one given time

Question 2

How do sigma factors in Prokaryotes mediate promoter recognition?

Answer 2

Sigma factors recognise the -10 and -35 motifs (highly conserved regions in prokaryotic promoters)

Question 3

What is meant by an abundant transcript?

Answer 3

A gene expressed in every cell aka Housekeeping gene

e.g. Glycolytic enzymes genes

Question 4

How are regulatory changes mediated?

Answer 4

Via regulatory transcription factors

Question 5

Outline how the LAC Operon switch regulates transcription?

Answer 5

1. LAC repressor binds upstream of of LAC Operon

2. prevents activation and transcription of LAC ZYA gene

Question 6

What are the different levels a gene can be transcribed to?

Answer 6

1. Abundant transcripts
2. Rare transcript
3. No transcript

Question 7

Why are TFII and Sigma factors able to recruit RNA?

Answer 7

Occurs at every promoter due to genetics

Question 8

What happens once the DNA is stably recruited to the Promoter?

Answer 8

RNA Pol. II is able to convert from a closed to an open complex
TATA box required to recruit TF

Question 9

How is tissue specific transcription carried out in β-globin?

Answer 9

β globin promoter has ubiquitous factors in all cell types
has tissue specific TF GATA-1
only present in genes that are expressed in rbc

Question 10

What do regulatory transcription factors do?

Answer 10

Dramatically alter RNA Pol.II recruitment and its ability to initiate transcription
In eukaryotes they influence local chromatin structure

Question 11

Which transcriptional switches are present in eukaryotes?

Answer 11

• Oestrogen Responsive Transcription
• Tissue specific transcription (β globin)
• Complex regulatory Cycle (cell cycle)

Question 12

What are rare transcript genes?

Answer 12

Genes that aren’t required as much and therefore are transcribed less

Question 13

What is the LAC Operon?

Answer 13

Prokaryotic paradigm for the regulation of transcription

- required for transport and metabolism of lactose in E.Coli

Question 14

What are Enhancers?

Answer 14

DNA sequences that enhance gene transcription by enhancing RNA Pol. recruitment to the promoter

Question 15

How can tamoxifen be used to treat breast cancer?

Answer 15

Tamoxifen - competitive inhibitor of oestrogen

- binds to oestrogen receptor blocking transcription of genes prevalent in breast cancer

Question 16

What is a transcriptome?

Answer 16

The segment of DNA that is Transcribed

Question 17

What is required for LAC gene to be transcribed?

Answer 17

In order for gene transcription:
Sigma factor binding sequence and promoter region required
When CAP protein binds to complementary sequence transcription occurs

Question 18

Where are enhancers found on the gene?

Answer 18

Enhancers can reside either 5’ or 3’ to a transcription unit can even be located on introns

Question 19

Why are factors required for promoter recognition in both pro and eukaryotes?

Answer 19

Neither prokaryotes or eukaryotes RNA Pol. form stable contacts with DNA
- they just slide along the duplex without being able to efficiently recognise promoters

Question 20

What other common regulatory transcription factors are present in eukaryotes?

Answer 20

1. NF-Kb: triggered by immune stress
2. CREB: triggered by Cyclic AMP
3. Oestrogen receptor: triggered by Oestrogen
4. ISGF3: triggered by Interferon

Question 21

Explain what is meant by no transcript genes

Answer 21

Genes that are never transcribed in some cells
However can be expressed a lot in other tissues i.e. tissue specific
e.g. Globin

Question 22

What are transcriptional switches?

Answer 22

Major biological regulatory mechanisms controlling the cell cycle and cell differentiation

Question 23

What is the significance of the LAC ZYA gene?

Answer 23

Genes need to utilise lactose as a carbon source when glucose not present
- LAC transcribed (CAP binds)

Question 24

What are inducible genes?

Answer 24

Genes that are transcribed via induction by certain stimuli

e.g. growth factors, viral infections, hormones etc.

Question 25

Which transcriptional switches are present in prokaryotes?

Answer 25

LAC Operon

Question 26

How are enhancers so specific to TF?

Answer 26

Contain DNA sequences that are very strong binding sites for TFs

Question 27

What is the role of the different areas in the eukaryotic promoter?

Answer 27

Regulatory Element GGGAAATTCC 5’-3’
- regulates recruitment of RNA Polymerase

TATA Box
- recruits general TF and then RNA Pol.II

Question 28

What is required in order for transcription to occur?

Answer 28

Recognition sequences that lie outside of gene transcription region in DNA

Question 29

How is the cell cycle regulated?

Answer 29

• Mitogenic signal allows cell to enter G1
• Checkpoints between each phase
• S, G2, M phase unaffected by extracellular environment
• CDK and Cyclin complexes

Question 30

What is the promoter region?

Answer 30

The sequence upstream of the coding region

Question 31

When does the LAC repressor bind to the promoter region?

Answer 31

When lactose and Glucose are present in the cell as bacteria prefer the use of glucose

Question 32

What is the role of the promoter region?

Answer 32

Recruit RNA Pol II to a DNA template strand

Question 33

How is promoter recognition mediated by initiation factors?

Answer 33

• sigma factors in prokaryotes

- TFII basal transcriptional machinary for eukaryotes

Question 34

Approximately how much of the prokaryotic genome is transcribed?

Answer 34

Only about 50% of prokaryotic genome

Question 35

How do transcription regulators recognise their target genes?

Answer 35

By interacting with the DNA without unwinding DNA