8A- Regulation Of Transcription And Translation Flashcards
What do transcription factors do?
They control the transcription of target genes.
All the cells in an organism carry the same genes but the structure and function varies because not all genes are expressed.
As different genes are expressed, different proteins are produced and these modify the cell and control the cell’s processes.
The transcription of genes is controlled by proteins called transcription factors.
How do transcription factors work?
In eukaryotes, transcription factors move from the cytoplasm to the nucleus.
They bind to specific DNA near the start of the target genes.
They control the rate of transcription.
Activators increase the rate of transcription. They help RNA polymerase bind.
Depressors decrease the rate of transcription. Preventing RNA polymerase from binding.
How can oestrogen initiate he transcription of target genes?
Oestrogen is a steroid hormone that can affect transcription by binding to a transcription factor called an oestrogen-oestrogen receptor complex.
This moves from the cytoplasm to the DNA where it binds bear the start of the target gene.
The complex is an activator of transcription, helps RNA polymerase bind.
How does RNA Interference (RNAi) inhibit the translation of mRNA?
Gene expression is affected by RNA interference.
Small double stranded RNA molecules stop mRNA from target genes being translated into proteins.
The molecules involved are small interfering RNA (siRNA) and miRNA (microRNA).
How does siRNA (and miRNA in plants) work?
The mRNA leaves the cytoplasm after transcription.
In the cytoplasm, double stranded siRNA associates with proteins.
The siRNA is complementary to the target mRNA.
The proteins cut the mRNA into fragments, so it can no longer be translated. The unusable pieces are then degraded.
How does miRNA work in mammals?
In mammals the miRNA isn’t usually fully complementary.
This makes it less specific than siRNA so it binds to more than one target.
It associates with proteins and binds to target mRNA in the cytoplasm.
The miRNA-protein complex physically blocks the translation of target mRNA.
The mRNA is then stored or degraded. When it’s stored, it can be returned and translated at another time.
What is the lac depressor?
E.coli is a bacterium that respires glucose, but it can use lactose if glucose isn’t available.
If lactose is present it makes an enzyme, ß-galactosidase, to digest it. If there’s no lactose it isn’t produced.
The production of the enzyme is controlled by a transcription factor- the lac repressor.
When there’s no lactose the lac repressor binds to DNA, stopping transcription.
When it is present it binds to the lac repressor, allowing transcription.
