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
