Factors Affecting Gene Expression Flashcards
What is cell differentiation
The process by which a cell becomes specialised for a particular function
What does a gene probe do
Allows a particular section of DNA and mRNA in a cell to be identified
How does a gene probe work
Probe finds exact sequence of nucleotides on the DNA
It is made with a complementary base sequence to the sequence it is looking for to do this
Heat the strands being studied
Probe can now find the DNA it complements and attaches to it (DNA hybridisation)
Fluorescent markers allow us to see where the probe is in the DNA
If you get the gene probe to target RNA instead you will only see the genes that are expressed
What is a transcription factor
A protein that moves from the cytoplasm to the nucleus and binds to specific DNA sites called promoter regions. Promoters are found at the start of their target gene.
What are the 2 types of transcription factor
Activators - help RNA polymerase to bind to the start of the target gene and activate transcriptions increasing transcription rate
Repressors - inhibit or decrease the rate of transcription by preventing RNA polymerase from binding to the target gene therefore stopping transcription
Process of a transcription factor
Hormone binds to transcription factor
This allows the transcription factor to enter the nucleus from the cytoplasm through a nuclear pore
This transcription factor can now bind to the promoter region in the DNA
This helps RNA polymerase to attach to the DNA chain and initiate transcription
Oestrogen as a transcription factor
Oestrogen enters the cell and binds to an oestrogen receptor inside the cell (transcription factor)
This forms a hormone receptor complex
This then moves to the nucleus where it binds to the promoter region before the target gene
This then acts as a promoter
What is pre mRNA
RNA produced at the end of transcription - includes introns and exons
What is splicing
Introns in the pre mRNA are removed by enzymes which cut them out
The exons are then joined together to form completed mRNA
mRNA then leaves the nucleus and enters the cytoplasm
What are spliceosomes
Enzyme complexes that join the remaining exons that are to be transcribed
How can spliceosomes lead to variation in the phenotype
They may join the same exons in a variety of different ways so a single gene can produce several versions of mRNA transcribed from the same DNA producing different proteins leading to more variation in the phenotype
What is epigenetics
The alteration of out phenotype or gene expression due to chemicals in the environment attaching to our histones or DNA
What are the two epigenetic mechanisms
Increased methylation of DNA
Decreased acetylation of histones
What are histones
Proteins which DNA is wound around to form chromatin
Chromatin can be condensed (accessible) or less condensed (not accessible) which controls whether a gene is expressed or not
DNA methylation
Adding a methyl group to DNA at the site where cytosine occurs next to guanine with a phosphate bond between them
It is added by DNA methyltransferase
This silences genes by changing the arrangement of the DNA molecule preventing transcription
DNA demethylation
Removal of methyl groups enables genes to be expressed
Occurs at the site where cytosine occurs next to guanine with a phosphate bind between them
Histone modification
DNA helices wraps around histones to form chromatin
Histones determine the structure of chromatin
When chromatin is supercoiled genes cannot be transcribed
Active chromatin is more loosely held together which allows for DNA to open up and therefore be transcribed
How many types of specialist cells is there
216
What are stem cells
Unspecialised cells that can divide and develop into other types of cells
How do stem cells specialise
They all contain the same genes but during development not all of them are transcribed and translated so certain genes are shut down by histone packing
What are the 4 types of stem cells
Totipotent - can create any cell type, occur for a short length of time in mammalian embryos
Pluripotent - can create most cell types, occur in embryo
Multipotent - can only produce a limited number of cell types, found in mature mammals
Unipotent - can only differentiate into one cell type, found in mature mammals
Stem cells stages of development
Cleavage (mitosis) occurs resulting in a mass of small, identical and undifferentiated cells forming a hollow sphere (totipotent) which then turns into a blastocyst (pluripotent)
What is therapeutic cloning
Experimental technique to produce large quantities of healthy tissue (e.g. to replace damaged cells)
Process of therapeutic cloning
Remove the nucleus from a patients normal body cell
Transfer it to a human ovum which has had its nucleus removed then fuse with an electric shock causing development
Pre embryo starts to develop and divide producing embryonic stem cells
The genetics perfectly match the patient so stem cells can be collected and cultured
They can then be transferred back into the patient
Positives and negatives of stem cell therapy
Positive - could avoid the risk of injection
Negative - nobody knows how the genes in cells are switched on or off to form particular types of tissue, could cause the development of cancers in the body
What are induced pluripotent stem cells
Cells that have been reprogrammed to be pluripotent again
Positives and negatives of induced pluripotent stem cells
Positives - removed the ethical issues of stem cells, removes the risk of injection
Negatives - it is very difficult to turn cells into pluripotent cells, it is even more difficult to persuade pluripotent cells to turn into the tissues wanted
Who can benefit from stem cell therapy
Parkinson’s disease - stem cells form dopamine neurones which grow and release dopamine reducing Parkinson’s
Type 1 diabetes - embryonic stem cells form a group of cells that look and work like insulin producing tissue
Damaged nerves - stem cells transplanted into rats with damaged spines and they managed to regain a certain amount of control and movement
Organs for transplants - take embryonic stem cells then manipulate differentiation of these stem cells into organs
iPS cells
Pluripotent so can be turned into most cell types by manipulation of transcription and epigenetics
Come form the individual patient so no risk of rejection
Doesn’t cause ethical issues like embryonic stem cells
Not as easy to grow and manipulate as embryonic stem cells
