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
what has recent research proved about cardiomyocytes
recent research has suggested that our hearts do not have some regenerative capability
Some scientists now think that old or damaged cardiomyocytes are replaced by new cardiomyocytes derived from a small supply of unipotent stem cells in the heart
some say this process is constantly occurring
some say it is a slow process and it is possible that some cardiomyocytes are never replaced throughout a person’s entire lifetime
what are adult stem cells
they are found in the body tissue of an adult
e.g. found in adult bone marrow
what are some limitations of using adult stem cells
they are not as flexible as embryonic stem cells as they can only specialise in a limited range of cells - so they are multipotent
although the operation is simple with very low risk, it can lead to a lot of discomfort in the patient
what are embryonic stem cells
these are obtained from embryos in the early stages of development
these embryos are created in a lab using in vitro fertilisation (IVF) - the egg cell is fertilised by sperm outside of the womb
Once the stem cells are approximately 4-5 days old, stem cells are removed from them and the rest of the embryo is destroyed
Embryonic stem cells can divide an unlimited number of times and develop into all types of body cells (they’re pluripotent)
what are induced pluripotent stem cells
iPS cells are created by scientists in a lab
The process involved “reprogramming” specialised stem cells to express a series of transcription factors that are normally associated with pluripotent stem cells
The transcription factors cause the adult body cell to express genes that are associated with pluripotency
how are the transcription factors introduced to the adult stem cell
once of the ways that these transcription factors can be introduced to the adult cells is by infecting them with a specially - modified virus
The virus has the genes coding for the transcription factors within its DNA
When the virus infects the adult cell, these genes are passed into the adult cell’s DNA meaning that the cell is able to produce the transcription factor
what are some ethical issues to consider when using stem cells for treatment
- obtaining stem cells from embryos raises ethical issues because the procedure results in the destruction of an embryo that could become a fetus of placed in a womb
Some people believe at the moment of fertilisation an individual is formed that has the right to live - so they believe that it is wrong to destroy embryos
benefits of stem cell therapy
- they could save many lives - e.g. many people are waiting for organ transplants could die before one is available
- it might be possible to make stem cells genetically identical to the patients’ own cells so reduce the chance of rejection
- they could improve the quality of life of many people
