module 6 - 19.2 regulation of transcription and translation (1) Flashcards
what is gene expression?
involves flow of genetic information from its origin in the nucleus to the ribosomes where polypeptides or proteins are synthesised
where does transcription occur?
nucleus of a cell
what is transcription?
involves formation of mRNA that carries a complementary DNA message to the ribosomes in the cytoplasm
where does translation occur?
ribosomes in cytoplasm of a cell
what is translation?
involves translation of mRNA message into specific sequence of amino acids to form a polypeptide or protein
how is gene expression controlled at the transcriptional phase?
transcription is prevented so mRNA is not synthesised
how is gene expression controlled at the post transcriptional phase?
the mRNA is controlled after it has been synthesised
how is gene expression controlled at the translational phase?
process of translation is prevented
how is gene expression controlled at the post translational phase?
the polypeptide is modified after it has been synthesised
what to proteins and transcriptional factors do?
- they activate the gene
- they are specific molecules that move from the cytoplasm and the nucleus
what do all transcriptional factors contain?
all contain DNA-binding domains which attach to specific sequences of DNA adjacent to the genes they regulate
what are the 2 classes of transcriptional factors?
- activators
- repressors
what are activators?
speed up the rate of transcription as they facilitate the binding of RNA polymerase to the start of the target gene and activate transcription
what are activators needed for?
needed for RNA polymerase to attach to the start of the target gene on the DNA chain
what are repressors?
they slow down the rate of transcription by binding themselves to the start of the target gene
- prevents RNA polymerase from binding
what happens when a gene is not being expressed?
the site on the transcriptional factor that binds to the specific nucleotide sequence in the DNA is blocked by a repressor molecule
how are transcriptional factors regulated?
- regulate signals produced by other molecules
- hormones activate transcriptional factors and so stimulate transcription
how does oestrogen affect the process of transcription?
- they affect specific genes which control cell growth by affecting transcription
- oestrogen is lipid soluble so diffuses easily through phosophlipid bilayer
- once inside, oestrpgen combines with an oestrogen receptor, forms oestrogen-receptor complex
what are the 2 oestrogen receptors?
- oestrogen receptor alpha
- oestrogen receptor beta
what does oestrogen receptor alpha act as?
an activator allowing the RNA to do its job
what happens when oestrogen binds to the oestrogen-receptor alpha complex?
- shape of DNA binding site on transcriptional factor changes and thus activates it
- activated transcriptional factor can then correctly employ its DNA-binding domains to attach to a specific sequence of DNA to regulated gene
what does oestrogen receptor beta act as?
a repressor, blocking the action of RNA polymerase
what does ER beta act as?
acts as a dominant inhibitor of ER alpha transcriptional activity in cells that express both receptors
how can oestrogens and their metabolic products initiate tumour growth?
- binding of an oestrogen to its ER stimulates cell division and DNA replication of mammary cells
- oestrogen metabolism can produce genotoxic and mutagenic products
- both processes disrupt cell cycle, apoptosis and DNA repair
