Chapter 8- Control of gene expression Flashcards
What is a mutation
A mutation is a spontaneous change to a base in the sequences of bases for one gene. It is likely to occur during DNA replication, during interphase in the cell cycle
What us a mutagenic agent
A mutagenic agent is something that increases the risk of a mutation. This includes; radiation ( alpha and beta particles and X-ray and gamma rays, ultraviolet light is not ionising but is still high enough to cause damage and disrupt the structure of DNA) and carcinogens
List the type of gene mutation
1) Addition
2)Deletion
3) Substitution
4) Inversion
5) Translocation
6) Duplication
What is an addition mutation and how can it impact the DNA sequence
It is the addition of an extra base being added to the sequence
The impact if adding one base is that all subsequent codons are altered. This is known as a frame shift to the right. This mutation can be very harmful because all the altered codons will code for different amino acids and result in a very different sequence of amino acids, which can result in a non-functioning protein
What is a deletion mutation and how can it impact the DNA sequence
It is the deletion of a base in a sequence
This causes a frame shift to the left. This could result in a different polypeptide chain, thus a non-functioning protein
What is a substitution mutation and how can it impact the DNA sequence
It is when one base has been swapped for a different base, but the number of bases stay the same and there is no frame shift. This results in only one codon changing, and due to the genetic code being degenerate it may still code for the same amino acid and so have no impact
What is an inversion mutation and how can it impact the DNA sequence
A section of bases detatch from the DNA sequence but when they rejoin, they are inverted, so the section of code is back to front. This results in different amino acids being coded for in this region
What is a translocation mutation and how can it impact the DNA sequence
A section of bases on one chromosome detatches and attaches to a different chromosome.
This is a substantial alteration and can cause significant impact on gene expression and therefore the resulting phenotype
What are stem cells
Stem cells are undifferentiated cells that can continually divide to become specialised.
What are the types of stem cells
- Totipotent
- Pluripotent
- Multipotent and unipotent
What are totipotent stem cells
Totipotent stem cells can divide and produce any type of body cell
During development, totipotent cells translate only part of their DNA, resulting in specialisation
Totipotent cells only occur during a limited time in early embryos
What are pluripotent stem cells
Pluripotent stem cells are found in embryos and can become almost any type of cell other than placenta cells
How are totipotent and pluripotent stem cells used in science and research
These stem cells are used in research with the prospect of using them to treat human disorders.
They can be used to regrow damaged tissue/cells in humans (Such as replacing burnt skin cells)
What are the issues of using pluripotent and totipotent stem cells
Sometimes the treatment doesn’t work or the stem cells continue to divide uncontrollably to produce a tumour
Additionally, ethically there is a debate on whether it is right to make a clone of yourself to make an embryo to get the stem cells, thus destroying the embryo.
What are multipotent and unipotent stem cells
These stem cells are found in mature mammals and can divide to form a limited number of cells, whereas unipotent cells can only differentiate into one type of cell
What are sources of stem cells
- Embryos; up to 16 days after fertilisation, containing stem cells that are pluripotent and can differentiate into any type of cell other than placenta cells
-Umbilical cord contains stem cells that are multipotent like adult stem cells - The placenta has stem cells that are multipotent and can develop into a limited number of cells
- Bone marrow contains adult stem cells and can produce different cells to repair those within a particular tissue or organ
What are induced pluripotent stem cells (IPS)
iPS cells can be produced from an adult somatic cell using appropiate protein transcription factors to overcome some of the ethical issues with using embryonic stem cells
1. iPS cells are created from adult unipotent cells. These cells, which can be from any body cell, are altered in the lab to return them to a state of pluripotency- they do this by switching all the genes back on to make the cell unspecialised. - This is done using transcriptional factors
They are very similiar to embryonic pluripotent stem cells, but do not cause the destruction of an embryo and the adult can give permission
The iPS have shown a self-renewal property, in that they can divide indefinetely to give limitless supplies. For these reasons, they could be used in medical treatment instead of embryonic stem cells
Define gene expression
Gene expression is when a protein is created.
In eukaryotic organisms, one way gene expression (protein synthesis) is controlled is by epigenetics.
Define epigenetics
Epigenetics are the heritable change in gene function without changing the DNA base sequence
These changes are caused by the environment and can inhibit transcription
Factors include: Diet, stress, and toxins can add epigenetics (chemical tags) to the DNA, which can control gene expression in eukaryotes
What is the epigenome
The epigenome is a single layer of chemical tags on DNA which impacts the shape of the DNA-histone complex and whether the DNA is tightly wound so won’t be expressed or unwound so it will be expressed
What happens if the DNA is highly/tightly wound
If the DNA is highly wound, then transcription factors cannot bind. Therefore, the epigenome, which is due to changes in the environment can inhibit transcription
Name 2 chemical tags (epigenetcis)
- Methylation
- Acetylation
Explain methylation of DNA
Increased methylation of DNA inhibits transcription as when methyl groups are added to DNA, they attach to the cytosine base.
This prevents transcriptional factors from binding and attracting proteins that condense the DNA-histone complex.
In this way, methylation prevents a section of DNA from being transcribed
Methylation of DNA and histones cause nucleotides to pack tightly together. Transcription factors cannot bind to the DNA, and genes are not expressed
Explain acetylation of DNA
Increased acetylation of DNA only bind to histones, therefore they have an opposite affect than methylation
Decreased acetylation of associated histones on DNA however inhibits transcriptopn
If acetyl groups are removed from the DNA, then histones become more positively charged and are attracted to the phosphate group in DNA
This makes the DNA and histones more strongly associated and harder for transcription factors to bind
Histone acetylation results in the loose packing of nucleosome transcription factors can then bind to DNA and genes are expressed.
