8.3 Regulation of transcription and translation

Question 1

What are transcription factors?

Answer 1

• Proteins which regulate transcription of specific target genes in eukaryotes
• By binding to specific DNA base sequences on a promoter region

Question 2

How do transcription factors regulate transcription?

Answer 2

• TFs move from cytoplasm to nucleus
• Bind to DNA at specific base sequences on a promoter region
• Helps or prevents RNA polymerase binding, stimulates or inhibiting transcription

Question 3

How does oestrogen affect transcription?

Answer 3

• Oestrogen is a lipid-soluble steroid hormone so diffuses into cell across phospholipid bilayer
• Oestrogen binds to receptor (an inactive TF), forming an oestrogen-receptor complex
• This changes the shape of the inactive TF, activating it
• This complex diffuses from the cytoplasm to the nucleus
• Then binds to a specific DNA base sequence on the promoter region of a target gene
• Helping RNA polymerase bind, stimulating transcription

Question 4

What is meant by epigenetics?

Answer 4

• Heritable changes in gene function without changing the base sequence of DNA
• Caused by changes in the environment

Question 5

What is meant by epigenome?

Answer 5

All chemical modification of DNA and histones (methylation of DNA and acetylation of histones)

Question 6

How can methylation inhibit transcription?

Answer 6

• Increased methylation of DNA
• So nucleosomes pack more tightly together
• Preventing RNA polymerase binding to promoter

Question 7

How can acetylation inhibit transcription?

Answer 7

• Decreased acetylation of histones
• Increases positive charge of histones so histones bind to DNA more tightly
• Preventing RNA polymerase binding to promoter

Question 8

What is RNA interference?

Answer 8

• Inhibition of translation of mRNA produced from target genes by RNA
• Inhibits expression of target gene

Question 9

How does RNA interference prevent translation?

Answer 9

• siRNA or miRNA binds to a protein, forming an RNA-induced silencing complex
• Single stranded siRNA / miRNA within RISC binds to target mRNA by complementary base pairing
• Leads to hydrolysis of mRNA fragments / prevents ribosome binding
• Preventing translation of target mRNA