The Control of Gene Expression: Gene Expression is Controlled by a Number of Features - Regulation of Transcription and Translation - Controlling Transcription & Oestrogen

Question 1

What is transcription?

Answer 1

• When a gene is copied from DNA into messenger RNA (mRNA)

Question 2

How is transcription triggered?

Answer 2

• RNA polymerase and transcription factors bind to the promoter region of a target gene
• The RNA polymerase and transcription factors assemble into a transcription initiation complex
• Once complex is in place, transcription can begin

Question 3

What is a promoter region?

Answer 3

• Specific DNA site found near the start of target genes

Question 4

Which enzyme is responsible for synthesising RNA from DNA?

Answer 4

• RNA polymerase

Question 5

What is the transcription of genes controlled by?

Answer 5

• Protein transcription factors

Question 6

What type of transcription factors are there?

Answer 6

• Activators

- Repressors

Question 7

How do transcription factors control gene expression?

Answer 7

• Transcription factors affect the rate of transcription
• In eukaryotes, transcription factors move from the cytoplasm to the nucleus
• In the nucleus they bind to promoter regions of target genes

Question 8

How do activators affect gene expression?

Answer 8

• Increase the rate of transcription

- Help RNA bind to the promoter region of target gene and activate transcription

Question 9

How do repressors affect gene expression?

Answer 9

• Decrease rate of transcription
• Bind to promoter region of target gene
• Prevent RNA polymerase from binding
• Transcription is prevented

Question 10

Under what circumstances will genes remain switched off?

Answer 10

• If transcription initiation complex failed to form
• If transcription initiation complex failed to bind to promoter region
• If transcription factors are absent
• If repressor molecules are present

Question 11

What steroid hormone can also affect gene expression? Does it act as an activator or repressor?

Answer 11

• Oestrogen

- Can act as either activator or repressor

Question 12

How does oestrogen affect gene expression?

Answer 12

• Oestrogen is lipid-soluble so can diffuse into cells
• Oestrogen binds to a transcription factor called an oestrogen receptor to form an oestrogen-oestrogen receptor complex
• This complex moves from cytoplasm to nucleus
• Complex binds to promoter region of target gene
• Can act as an activator and help RNA polymerase to bind to promoter region
• Can act as repressor by binding to promoter region of target gene to block RNA polymerase from binding

Question 13

What determines whether the oestrogen-oestrogen receptor complex will act as an activator or a repressor?

Answer 13

• Depends on the type of cell

- Depends on the target gene

Question 14

Why does oestrogen not affect gene expression in all cells?

Answer 14

• Not all cell types have oestrogen receptors