Transcriptional circuits in prokaryotes and eukaryotes

Question 1

What is a transcriptome?

Answer 1

Segment which is transcribed is known as the transcriptome

Question 2

What percentage of the prokaryotic genome is transcribed?

Answer 2

Only about 50%

Question 3

What amount of the transcribed at any one time?

Answer 3

Only a fraction

Question 4

What is an abundant transcript?

Answer 4

type of gene gives rise to many copies of RNA

Question 5

What is a rare transcript?

Answer 5

where not as many RNA copies are produced

Question 6

What is a no transcript and example?

Answer 6

type of gene has no transcript in some type of cells like beta globin genes which are only expressed in red blood cells

Question 7

What are inducible genes?

Answer 7

Where transcription is induced by a stimuli

Question 8

What does the stimulation of an inducible gene result in?

Answer 8

This results in a gene which is a rare or no transcript to become an abundant transcript

Question 9

What is a promoter region?

Answer 9

Recruit RNA polymerase to a DNA template

Question 10

How many directions does RNA polymerase move in?

Answer 10

RNA polymerase only moves in one direcrion

Question 11

What are enhancers?

Answer 11

DNA sequences which increase transcription

Question 12

Where do enhancers reside?

Answer 12

Can reside 5’ or 3’ to a transcription unit and also found in introns

Question 13

What do enhancers contain?

Answer 13

Contain DNA sequences which contain very strong binding sites for transcription factors

Question 14

Where are enhancers located in terms of the transcription site?

Answer 14

Not immediately adjacent to the site of transcription

Question 15

What do RNA polymerase do along the complex?

Answer 15

RNA polymerase slides along the duplex without being able to efficiently recognise promoters

Question 16

What factors allow the recognition of promoter in prokaryotes?

Answer 16

Sigma factors

Question 17

What factors allow the recognition of promoter in eukaryotes?

Answer 17

TFII basal transcriptional machinery

Question 18

What happens once RNA polymerase binds to DNA?

Answer 18

Once RNA polymerase binds to DNA, converted from a closed to an open compound

Question 19

What do sigma factors do?

Answer 19

Sigma factors recognises the -35 and -10 motifs common to prokaryotes and enables RNA polymerase to make stable contact with DNA

Question 20

What is a consensus sequence?

Answer 20

DNA having similar structure and function in different organisms

Question 21

How is the consensus sequence determined?

Answer 21

Determined by aligning many nucleotide sequences that share a common function then determining the most commonly expressed nucleotide at each position

Question 22

Why is the TATA box needed

Answer 22

TATA box is needed to recruit general transcription factors and then RNA polymerase

Question 23

What happens to the Lac operon when there are low levels of glucose?

Answer 23

§ CAP protein binds to the promoter region under low glucose level and RNA polymerase binds to the promoter region
□ Lactose will bind to the LAC repressor and RNA polymerase will transcribe the LAC ZYA gene.

RNA formed translated into proteins which utilise energy from Lactose

Question 24

What happens to the Lac operon when theres sufficient amount of glucose?

Answer 24

LAC repressor binds to promoter region when there’s sufficient amount of glucose

This prevents transcription

Question 25

How does oestrogen-responsive transcription work?

Answer 25

§ Oestrogen binds to oestrogen receptor complex

This changes the shape of the receptor protein allowing the hormone-receptor complex to enter the nucleus and bind to the oestrogen responsive element and induce the expression of the genes

Question 26

What is tissue specific transcription(example based answer)?

Answer 26

Tissue specific factors like GATA-1(Red blood cells) recruit transcription factors and ensure transcription occurs in specific tissue

Question 27

What are cdks?

Answer 27

Cdks are enzymes which phosphorylate transcription factors

Question 28

What do cdks depend on?

Answer 28

Cdks are cyclin dependent

Question 29

What activates promoters for G1/S transition genes?

Answer 29

Promoters for G1/S transition genes are activated by a factor called E2F

Question 30

What happens to E2F activity during G0 and early G1?

Answer 30

E2F activity is repressed in G0 and early G1 by the product of the retinoblastoma gene

Question 31

What is a common target in cancer?

Answer 31

Retinoblastoma is a common target in cancer

Question 32

Why are regulatory elements needed?

Answer 32

Needed to regulate the recruitment of RNA polymerase

Question 33

What do regulatory factors bind to?

Answer 33

Regulatory factors bind to the promoter region and help recruit general transcription factors

Question 34

What is tamoxifen?

Answer 34

It is an antagonist

Question 35

What does tamoxifen do to treat breast cancer?

Answer 35

Used to treat breast cancer by competing with oestrogen receptor complex to bind to oestrogen receptor complex and preventing transcription as RNA polymerase is unable to bind.