more on gene expression Flashcards
what is the job of a transcription factor
transcription factors move from the cytoplasm to the nucleus in eukaryotes
They then bind to specific DNA sites called PROTOMERS, which are found at the start of their target gene - which are the genes they control the expression of
what do the transcription factors called “activators” fo
they stimulate or increase the rate of transcription e.g. they help RNA polymerase bind to the start of the target gene and activate transcription
what do the transcription factors called “repressors” do
these inhibit or decrease the rate of transcription e.g. they bind to the start of the target gene, preventing RNA polymerase from binding, stopping transcription
what is oestrogen
the expression of genes can also be affected by other molecules in the cell e.g.
oestrogen is a steroid hormone that can affect transcription by binding to a transcription factor called an oestrogen receptor
how does oestrogen affect the expression of transcription
oestrogen binds to the transcription factor called an oestrogen receptor
this forms an oestrogen - oestrogen receptor complex
the complex moves from the cytoplasm into the nucleus where it binds to specific DNA sites near the start of the target gene
The complex can act as an activator e.g. helping RNA polymerase bind to the start of the target gene
what is RNAi
in eukaryotes, gene expression is also affected by RNA interference (RNAi)
RNAi is where small, double-stranded RNA molecules stop mRNA from target genes being translated into proteins
A similar process to RNAi also occurs in prokaryotes.
what are the molecules involved in RNAi called
they are called siRNA (small interfering RNA) and miRNA (microRNA
how does RNAi work (involves siRNA and miRNA in plants)
once mRNA has been transcribed, it leaves the nucleus for the cytoplasm
in the cytoplasm, double-stranded siRNA associates with several proteins and unwinds
One of the resulting single strands of siRNA is selected and the other strands are degraded
the single strand of siRNA then binds to the target mRNA. The base sequence of the siRNA is complementary to the base sequence to base sequence in sections of the target mRNA
The proteins associated with the siRNA cut the mRNA into fragments - so it can no longer be translated. The fragments then move into a processing body which contains “tools” to degrade them
this process is similar to miRNA in plants, however. its production is similar to that of mammalian miRNA
why is miRNA less specific than siRNA
the miRNA is not usually fully complementary to the target mRNA therefore us is less specific than siRNA and so it may target more than one mRNA molecules
what happens when miRNA is first transcribed
it exists as a long folded strand
It is processed into a double strand, and then into two single strands by enzymes in the cytoplasm
Like siRNA, one strand associates with proteins and binds to target mRNA in the cytoplasm
Instead of the proteins associated with miRNA cutting mRNA into fragments, the miRNA - protein complex physically blocks the translation of the target mRNA
The mRNA is then moved into a processing body where it can either be stored or degraded
When it is stored it can be returned at translated at another time
how do stem cells become specialised
stem cells become specialised because during their development they only transcribe and translate part of their DNA
stem cells all contain the same genes but during development not all of them are transcribed and translated (expressed)
under one set of conditions, certain genes are expressed and others are switched off
what happens to the genes that are expressed
the genes that are expressed get transcribed into mRNA
which is then translated into proteins
These proteins modify the cell - they determine the cell structure and control cell processes (including the expression of more genes, which produced more proteins)
it is these changes to the cell by these proteins that causes the cell to become specialised
The change is difficult to be reversed so once a cell is specialised it stays specialised
summarise how a cell becomes specialised
Genes are expressed 🠮 mRNA is transcribed and translated into proteins 🠮 proteins modify the cell 🠮 cell becomes specialised for a particular function
Genes are switched off 🠮 mRNA not transcribed or translated
what are cardiomyocytes
cardiomyocytes are heart muscle cells that make up a lot of the tissue in our hearts i
what was a common misconception about cardiomyocytes
it was thought that in mature mammals, they could not divide to replicate themselves
therefore everyone thought that we were not able to regenerate our own heart cells at all
This is a problem if the heart becomes damaged
