Controlling Gene Expression Flashcards
Pre-transcriptional control
By simple diffusion oestrogen enters the cell
Oestrogen binds to an oestrogen receptor forming a
Transcription factor (TF) complex TF complex changes shape and enters nucleus through nuclear pore
TF binds to the promoter and stimulate/inhibits transcription.
Encourages/inhibits RNA polymerase binding to the gene
Post-transcriptional control
Double stranded RNA formed
DICER enzyme hydrolyses RNA to form small interfering RNA (siRNA)
siRNA becomes single stranded and binds to RISC enzyme to form a complex SiRNA binds to complementary bases on mRNA
RISC enzyme hydrolyses the mRNA
Translation prevented
Gene is not expressed
Epigenetics
Chemical tags added to histones or DNA which can be inherited
Changes the expression of the gene
No change to the DNA base sequence
Methylation of DNA
Methyl groups added to cytosine bases on DNA
Methyl groups prevent attachment of RNA polymerase to promoter
Prevents transcription
Acetylation of histones
Acetyl groups added to histones
Positive charges on acetyl groups causes histones to repel each other
Reduces the condensation of DNA on to histones
Easier for transcription factors to attach to promoter
Increased/decreased rate of transcription
Proto-oncogenes
Group of genes that increase cell division
Promotes the transcription and translation of cell division proteins
Oncogene
Mutated proto-oncogene becomes an oncogene
Leads to cell becoming cancerous
Mutations are usually dominant
Gene permanently turned on
More transcription and translation of gene
Increases rate of cell division
Tumour suppressor genes
Genes that reduce cancer
Codes for protein which increases cell apoptosis and reduces rate of cell division
Mutated tumour suppressor genes
Increased methylation, decreased acetylation or mutation results in less transcription Less mRNA made results in less translation
Less protein produced
Leads to increased rate of cell division or decreased cell apoptosis
Increases uncontrolled division of cells→cancer
