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 or disulfide bridges
-tertiary structure folds diff
- 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 sustitution
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
