Regulation of transcription and translation

Question 1

What are transcription factors?

Answer 1

Proteins that aid the transcription of DNA

Question 2

Describe the role of transcription factors.

Answer 2

• Bind to a ‘promoter site’ where there is a specific base sequence section (before the target genes)
• Binding stimulates the transcription of the target gene
• mRNA forms a complex with the t.f. so that this gene can be expressed after transcription occurs
• This ensures that only specific genes are expressed

Question 3

What is a repressor?

Answer 3

A transcription factor that prevents a gene from being expressed

Question 4

What is an activator?

Answer 4

A transcription factor that promote the expression of a gene

Question 5

What is siRNA?

Answer 5

A repressor

Question 6

Describe the role of siRNA as a transcription factor

Answer 6

• Double stranded RNA molecule is hydrolysed by an enzyme into double stranded siRNA
• An enzyme binds to one strand of siRNA and breaks it apart to form single strands
• siRNA undergoes complementary base pairing with mRNA
• Cuts mRNA into fragments, prevents translation

Question 7

Describe the role of oestrogen in transcription

Answer 7

• Lipid soluble, so it diffuses through the phospholipid bilayer
• Binds to a receptor site on a transcription factor
• This changes the shape of the DNA binding site on the transcriptional factor
• This allows the transcriptional factor to bind to DNA
• This stimulates transcription

Question 8

What is epigenetics?

Answer 8

The heritable changes in gene function, without changes to the base sequence of DNA.

Question 9

What is methylation?

Answer 9

• CH₃ group added to CpG site (cytosine and guanine)
• Prevents transcription factor from interacting with the gene
• Gene not expressed

Question 10

What is acetylation?

Answer 10

• COCH₃ added to histones to make DNA less tightly wound, which allows binding of transcription factor
• Decreased acetylation means that fewer transcription factors can bind to the DNA
• Stops gene expression

Question 11

What leads to epigenes?

Answer 11

• Increased methylation

- Decreased acetylation

Question 12

What are the consequences of epigenetics?

Answer 12

• Can result in genetic diseases such as fragile X syndrome and Prader-Willi syndrome

Question 13

How do benign tumours differ from malignant tumours?

Answer 13

Malignant tumours metastasise

Question 14

Describe the causes and treatments of cancer

Answer 14

• Rapidly dividing cells
• Caused by mutations in DNA
• Can metastasise
• Can be treated with chemotherapy or radiation
• Biopsies can identify cancer

Question 15

What genes are associated with cancer?

Answer 15

• Proto-oncogenes

- Tumour suppressor genes

Question 16

What do proto-oncogenes do?

Answer 16

• Stimulate cell division
• Only stimulated when growth factors are detected
• A mutation mutates proto-oncogenes into oncogenes which a permanently expressed to stimulate cell division
• Causes tumours to grow

Question 17

What do tumour suppressor genes do?

Answer 17

• They inhibit cell division

- Made inactive by increased methylation

Question 18

What do growth factors do?

Answer 18

Bind to membrane bound receptors which stimulates the binding of transcription factors to mRNA to start transcription.