8.2.2 Regulation of transcription and translation ( topic 8 control of gene expression)

Question 1

what are transcription factors

Answer 1

• proteins which regulate transcription of specific target genes in eukaryotes
• by binding to a specific DNA base sequence on a promoter region

Question 2

Describe how transcription can be regulated using transcription factors

Answer 2

1) transcription factors move from cytoplasm to nucleus
2) bind to DNA at a specific DNA base sequence on a promoter region
3) this stimulated or inhibits transcription ( production of mRNA) of target genes by helping or preventing RNA polymerase binding

Question 3

Explain how oestrogen affects transcription

Answer 3

1) Oestrogen is a lipid soluble steroid hormone so diffuses into cell across phospholipid bilayer
2) In cytoplasm , oestrogen binds to its receptor , an inactive transcription factor , forming an oestrogen - receptor complex
3) This changed the shape of the inactive transcription factor , forming an active transcription factor
4) The complex diffuses from cytoplasm into the nucleus
5) Then binds to a specific DNA base sequence on the promoter region of a target gene
6) Stimulating transcription of target genes forming mRNA by helping RNA polymerase to bind

Question 4

Explain why oestrogen only affects target cells

Answer 4

Other cells do not have oestrogen receptors

Question 5

describe what is
meant by epigenetics

Answer 5

• heritable changes in gene function without changes to the base sequence of DNA
• caused by changes in the environment

Question 6

describe what is meant by epignome

Answer 6

all chemical modification of DNA and histone proteins - methyl groups on DNA and acetyl groups on histone

Question 7

summarise the epigenetic control of gene expression in eukaryotes

Answer 7

to inhibit transcription:
methylation in dna = increased
acetylation of histone = decreased
to allow transcription :
methylation in DNA = decrease
acetylation of histones = increased

Question 8

explain how methylation and acetylation can inhibit transcription

Answer 8

1) increased methylation of DNA - methyl groups added to cytosine bases in DNA
2) so nucleosomes (dna wrapped around histone ) pack more tightly together
3) preventing transcription factors and rna polymerase binding to promoter

1) Decreased acetylation of histones increased positive charge of histones
2) so histones bind DNA more tightly
3) preventing transcription factors and RNA polymerase binding to promoter

Question 9

explain the relevance of epigenetics on disease debelopent and treatment

Answer 9

• environmental factors can lead to epigenetic changes
• these can stimulate / inhibit expression of certain genes that can lead to disease development
  • increased methylation of DNA or decreased acetylation of histones inhibits transcription
  • decreased methylation of DNA or increased acetylation of histones stimulated transcription
• diagnostic tests can be developed that detect these epigenetic changes before symptoms present
• drugs can be developed to reverse these epigenetic changes

Question 10

describe the regulation of translation by RNA interference

Answer 10

1) small interfering RNA or micro rna is incorporated into / binds to a protein , forming an RNA - induced silencing complex (RISC)
• siRNA synthesised as a double stranded RNA => 1 strand incorporated
• miRNA synthesised as a double standee hairpin bend of RNA => borh strands incorporated
2) single stranded miRNA / siRNA within RISC binds to target mRNA with a complementary base sequence
3) this leads to hydrolysis of mRNA into fragments which are then degraded or prevents ribsomones binding
4) reducing / preventing translation of target mRNA into protein