20.3 regulation of transcription & translation

Question 1

how is a gene switched on?

Answer 1

transcription factors bind to promotor region

Question 2

when is a gene switched off?

Answer 2

DNA binding site on transcription factor is not active

Question 3

how does oestrogen affect gene expression?

Answer 3

oestrogen binds to a receptor site on transcription factor & activates dna binding site

Question 4

explain the process of stimulating transcription by oestrogen.

Answer 4

1- oestrogen diffuse through phospholipid bilayer since it’s lipid-soluble
2- oestrogen binds to site on a receptor molecule of the transcription factor which are complementary to each other
3- binding of oestrogen causes change in shape of DNA binding site
4- transcription factors enter nucleus (through nuclear pores) & binds to promotor region of DNA

Question 5

describe the 2 structures of siRNA.

Answer 5

• short, double-stranded RNA
• 2 overhanging nucleotides at 3’ end

Question 6

what does siRNA do?

Answer 6

cause degradation of mRNA & stops translation

Question 7

how does siRNA stop translation? (4)

Answer 7

1- enzyme cuts large double-stranded mRNA to siRNA
2- siRNA binds with RISC proteins -> RISC complex & loses 1 strand of siRNA
3- RISC complex binds to mRNA by complementary base pairing

4a- exactly complementary: mRNA is degraded
b- partly complementary: siRNA remains bound & stops translation