3.8.2.2 Regulation of transcription and translation

Question 1

What is a transcription factor?

Answer 1

Proteins which bind to a promoter region on the DNA (complementary shape) and stimulate RNA polymerase to produce mRNA

Question 2

How is transcription inhibited?

Answer 2

• Repressors decrease the rate of transcription (reduce mRNA, reduce protein made)
• Bind to the promoter region and prevent RNA polymerase from binding
• Or can bind to the transcription factor so it cannot bind to the DNA

Question 3

What happens without transcription factors?

Answer 3

• RNA polymerase canot bind
• mRNA isn’t made, proteins not made
• gene not expressed

Question 4

How does oestrogen initiate transcription?

Answer 4

• osestrogen is small and hydrophobic (lipid soluble) so can diffuse through membrane into cells
• bind to the transcription factor oestrogen receptor, which changes shape and releases it
• oestrogen-oestrogen receptor complex enters nucleus and binds to promoter region of one of its target genes, stimulating RNA polymerase to transcribe target gene

Question 5

What is RNA interference?

Answer 5

• siRNA and miRNA inhibit translation by binding to mRNA
• they are double stranded RNA but when activated they unwind to become single stranded and bind to mRNA by complementary base pairing preventing translation
• this triggers other enzymes to destroy the mRNA

Question 6

Define epigenetics

Answer 6

heritable changes in gene expression without changing the base sequence of DNA

• can be inherited by offspring or daughter cells during mitosis

Question 7

Epigenetic control of gene expression in eukaryotes

Answer 7

• DNA is wrapped around histone proteins
• If DNA is tightly coiled, genes are inactive as TF can’t bind
• chemicals may attach to histones or DNA to affect coiling
• no changes to the base sequence of DNA

Question 8

How does increased methylation (hyper methylation) of DNA inhibit transcription?

Answer 8

• methyl groups bind to DNA promoter region of gene
• the transcription factor cannot bind
• RNA polymerase isn’t stimulated
• transcription doesn’t occur

Question 9

How does methylation cause cancer?

Answer 9

• methyl groups added to tumour suppressor genes which produce proteins that reduce cell division
• methylation inhibits transcription of these genes stops the proteins being made
• leading to cancer as cell division occurs uncontrollably

Question 10

How does decreased acylation inhibit transcription?

Answer 10

• Acetyl COCH3 groups bind to histone proteins
• Acylation causes DNA to uncoil/decondense - gene is more uncovered so transcription factors/RNA polymerase can bind
• if the acetyl groups are removed from the histones, DNA condenses, the TF cannot bind, RNA polymerase not stimulated, no transcription