8.2.2 Regulation of transcription and translation

What is a transcriptional factor?

proteins which stimulate or inhibit transcription of target genes

How do transcriptional factors enter the cell?

move from cytoplasm into nucleus

How do transcriptional factors regulate transcription in a cell?

• bind to specific DNA base sequence on promoter region

• stimulates/inhibits transcription by helping/preventing RNA polymerase from binding to DNA

How does oestrogen enter a cell?

steroid (lipid-soluble) hormone which diffuses into cell across phospholipid bilayer

How is oestrogen involved in initiating transcription?

• binds to receptor of transcriptional factor (as it is complementary)

• forms oestrogen-receptor complex

• changes shape of DNA binding site of transcription factor to make it complementary promotor region

Why does oestrogen only affect target cells?

only binds to cells with oestrogen receptors

Define epigenetics

heritable changes in gene function, without changes to base sequence of DNA, caused by the environment
(changes occur to epigenome)

What environmental factors can cause changes to the epigenome?

diet, stress, toxins

What is meant by epigenome

chemical modification of DNA and histone proteins

What mechanisms causes the epigenome to alter to inhibit transcription?

• inceased methylation of DNA

• decreased acetylation of histones

What is methylation of DNA?

adding methyl groups to cytosine bases in DNA

How does increased methylation inhibit transcription?

• increased methylation of DNA causes more methyl groups to be added to DNA

• DNA is tightly wrapped around histones

• more difficult for transcription factors to bind

What is acetylation of histones?

acetyl group is added to histone proteins

How does decreased acetylation inhibit transcription?

• decreased acetylation of histones causes histones to become more positively charged

• histones tightly bind to DNA

• more difficult for transcription factors to bind

How can methylation lead to cancer?

hypermethylation of TSG could result in gene being inactivated and switched off

Describe how RNA interference (RNAi) inhibits transcription

mRNA produced from target genes is destroyed before it is translated ysing small interfering RNA (siRNA)

How is siRNA produced?

enzyme cuts mRNA into siRNA

Describe how siRNA destroys mRNA to inhibit translation

• siRNA combines with (another) enzyme forming an siRNA-enzyme complex

• binds via complementary vase pairing to another mRNA molecule

• enzyme cuts up mRNA so it cannot be translkated