Gene mutation Flashcards
what is a gene mutation
change in the sequence of base pairs in a DNA molecule that may result in an altered polypeptide
where do the errors in Dna often occur
in S phase - where gene replication occurs
how can mutations occur
changes to the DNA sequence that occur spontaneously or continuously
what are mutagenic agents
substances, chemical or physical, that can increase the likelihood of a mutation occurring
what are the consequences of mutations
the DNA is passed onto the next generation of cells - so this could result in a change in the protein/ enzyme produced which can be inherited by next gens
what happens to the structure of a protein when a mutation occurs
-primary structure - change in amino base sequence
-secondary - may not produce h-bonds
-tertiary structure folds diff-or disulfide bridges
- so enzyme and substrate no longer complementary so cannot bind
what are the types of gene mutation
-substitution
-inversion
-insertion
-deletion
-duplication
-translocation
what is an insertion mutation
occurs when a nucleotide (with a new base) is randomly inserted into the DNA sequence is known as an insertion mutation
-insertion mutation changes the amino acid that would have been coded for by the original base triplet, as it creates a new, different triplet of bases
This is because every group of three bases in a DNA sequence codes for an amino acid
An insertion mutation also has a knock-on effect by changing the triplets (groups of three bases) further on in the DNA sequence
-This is sometimes known as a frameshift mutation
This may dramatically change the amino acid sequence produced from this gene and therefore the ability of the polypeptide to function
what is deletion
occurs when a nucleotide (and therefore its base) is randomly deleted from the DNA sequence is known as a deletion mutation
Like an insertion mutation, a deletion mutation changes the amino acid that would have been coded for
Like an insertion mutation, a deletion mutation also has a knock-on effect by changing the groups of three bases further on in the DNA sequence
This is sometimes known as a frameshift mutation
This may dramatically change the amino acid sequence produced from this gene and therefore the ability of the polypeptide to function
what is substitution
occurs when a base in the DNA sequence is randomly swapped for a different base is known as a substitution mutation
-Unlike an insertion or deletion mutation, a substitution mutation will only change the amino acid for the triplet (group of three bases) in which the mutation occurs; it will not have a knock-on effect
what are the 3 types of substitution mutation
-silent
-missense
-nonsense
what is a silent mutation
a mutation that does not alter the amino acid sequence of the polypeptide (this is because certain codons may code for the same amino acid as the genetic code is degenerate)
what is a missense mutation
mutation alters a single amino acid in the polypeptide chain (sickle cell anaemia is an example of a disease caused by a single substitution mutation changing a single amino acid in the sequence
what are nonsense mutations
mutation creates a premature stop codon (signal for the cell to stop translation of the mRNA molecule into an amino acid sequence), causing the polypeptide chain produced to be incomplete and therefore affecting the final protein structure and function (cystic fibrosis is an example of a disease caused by a nonsense mutation, although this is not always the only cause)
what is an inversion mutation
sequence of bases are reversed
what is duplication
A whole gene or section of a gene is duplicated so that two copies of the gene/section appear on the same chromosome
The original version of the gene remains intact and therefore the mutation is not harmful
Overtime, the second copy can undergo mutations which enable it to develop new functions
Duplication mutations are an important source of evolutionary change
Alpha, beta and gamma haemoglobin genes evolved due to duplication mutations
what is translocation of a gene section
gene is cut in two places
The section of the gene that is cut off attaches to a separate gene
The result is the cut gene is now non-functional due to having a section missing and the gene that has gained the translocated section is likely to also be non-functional
If a section of a proto-oncogene is translocated onto a gene controlling cell division, it could boost expression and lead to tumours
Similarly, if a section of a tumour suppressor gene is translocated and the result is a faulty tumour suppressor gene, this could lead to the cell continuing replication when it contains faulty DNA
why do some mutations not have an effect
-the code is degenerate, so more than one triplets codes for the same AA
-could be in an intron and removed in splicing
how can mutations be positive
-could have advantages for the organism
-enable them to increase survival and pass on alleles
-leads to evolution
what are some mutagenic agents
High energy ionising radiation, such as alpha, beta or gamma radiation
Chemicals, such as nitrogen dioxide or benzopyrene from tobacco smoke
what is a stem cell
undifferentiated cell that can divide,to produce offspring, undergo differentiation and become specialised- to give a particular function
what does potency/plasticity
ability of stem cells to differentiate into more specialised cell types is known as
how do stem cells become specialised
they transcribe and translate parts of their DNA, due to where they are/ conditions that they are in the body
-only some genes are expressed and the rest are switched off
what are the 4 types of stem cells
-totipotent
-pluripotent
-multipotent
-unipotent
what are totipotent cells
-cells that can differentiate into embryonic and extra-embryonic tissues
-found in the embryo and last for around 3-4 days after fertilisation
-all genes are activated
what are pluripotent cells
-cells that can differentiate into any of the 3 types of germ layers of the cell - but not able to differentiate into extra-embryonic cells
-occurs early in embryos of mammals around day 5-7
-vast majority of genes are still able to be activated
what are multipotent cells
-adult stem cells
-can divide to from different cells types but not all
-eg cells in bone marrow that form blood cells
-some genes have been switched off but they have the genes from some different cells
what are unipotent cells
-cells that can only form one other type of cell
-heart muscle cells (cardiomyocytes) can generate new cardiomyocytes through the cell cycle to build and replace heart muscle
-lots of genes have been switched off va the regulation of transcription factors
why can stem cells be used in medicine
due to their potency - thus availability to differentiate - and can be used to grow organs and tissues for treatment of a variety of conditions
why is the use of stem cells objected
-unused IVF embroys can be donated to research instead of being destroyed - some object as destruction of a potential fetus - right to life
-egg cells frozen for IVF which have not been fertilised that can be stimulated to divide - less objection as they would not survive after for a few days if implanted into a womb
-use of adult stem cells is more ethical - however they cannot develop into all the specialised cells that embryonic stem cells
what are adult stem cells
obtained from the body tissue and bone marrow of an adult
how can adult stem cells be removed
simple operation that carries little risk although it can be quite uncomfortable
why can adult stem cells not differentiate into as many cells as embryonic
they are multipotent - so are less potent
how can adult stem cells be used
bone marrow transplants can replace faulty bone marrow that produces abnormal blood cells eg sickle-cell anemia
used to treat paralysis
what are induced pluripotent stem cells (iPS)
stem cells grown in a lab from specialised adult stem cells
-iPS cells have been developed by scientists using an adult’s somatic cells that are unipotent (fully differentiated)
-As all somatic cells contain the same genetic material scientists are able to use specific transcription factors to target the genes that control pluripotency
-Scientists ‘switch on’ these genes that are usually silenced in differentiated cells which allows them to revert back to pluripotent cells
-enables them to become as potent as embryonic stem cells and obtained without the ethical obligations
why are iPS cells safer for patients
made from own cells so less likely to be rejected and reduce wait time for the transplants
what are future stem cell therapies
use of stem cells to replace diseased or damaged organs such as the bladder
or to replace damaged tissue eg in the trachea
