8 - Gene mutations Flashcards
DNA damage
Physical abnormalities in DNA (e.g. single and double stranded breaks)
Mutation
Change in the base sequence of the DNA
Somatic mutation
Occur in non-reproductive cells and are passed to new cells through mitosis, creating a clone of cells with the mutant gene
Germ line mutation
Occur in cells that give rise to gametes. Meiosis and sexual reproduction allow germ line mutations to be passed to half the members of next generation
Which base pairs have 2 hydrogen bonds
A and T, C and G have 3
Purine
Adenine and guanine (Pure As Gold). Larger due to two ring structure
Pyrimidines
Cytosine, Thymine and uracil. Smaller due to single ring structure
Base substitution
Changes the base of a single DNA nucleotide
Transition
Base substitution in which a purine replaces a purine or pyrimidine replaces a pyrimidine
Transversion
Base substitution in which a purine replaces a pyrimidine or a pyrimidine replaces a purine
Insertion
Addition of one or more nucleotides, may lead to frameshift, usually alter all amino acids following the mutation
Deletion
Deletion of one or more nucleotides, may lead to frameshift, usually alter all amino acids following the mutation
Frameshift mutation
Insertion or deletion that alters the reading frame of a gene
in frame deletion or insertion
Deletion or insertion of a multiple of three nucleotides that does not alter the reading frame
expanding nucleotide repeats
Mutations in which number of copies of a set of nucleotides increases in number
how can increases in repeat number cause
disease
- Nucleotide expands within coding part
of gene, extra amino acid residues
added, eg. Huntington disease - Repeat may be outside coding region,
but may affect gene expression, eg.
Fragile X syndrome
Forward mutation
Changes the wild-type phenotype to a mutant phenotype
reverse mutation
Changes a mutants phenotype back to the wild type phenotype
Missense mutation
The new codon encodes for a different amino acid. There is a change in amino acid sequence
nonsense mutation
The new codon is a stop codon, there is a premature termination of translation
silent mutation
New codon encodes the same amino acid, there is no change in the amino acid sequence
Neutral mutation
Changes the amino acid sequence of a protein without altering its ability to function (chemically similar amino acid)
Loss of function mutation
Causes complete or partial loss of function
gain of function mutation
Causes the appearance of a new trait or function
Lethal mutation
causes death
suppressor mutation
Suppresses the effect of an earlier mutation at a different site
Intragenic suppressor mutation
Suppresses the effect of an earlier mutation within the same gene by changing a second nucleotide in the same codon or suppressing a frameshift mutation
Intergenic suppressor mutation
Suppresses the effect of an early mutation in another gene
Depurination
Spontaneous chemical change that causes loss of purine base from nucleotide. Results when covalent bond connecting purine to 1’-carbon atom of deoxyribose sugar breaks. Produces apurinic site
Deamination
Loss of amino group from a base. May be spontaneous or induced by mutagenic chemicals. Can alter pairing properties of a base
Base analogs
Chemical mutagens with structures similar to that of the four standard bases. DNA polymerase cannot distinguish between these analogs.
Pyrimidine dimers
Result from UV light, pyrimidine dimers are usually two thymine bases. Distorts DNA helix and blocks replication
Phenotypic effects of mutations
- Forward mutation and Reverse mutation
- Neutral mutation
- Loss of function mutation
- Gain of function
- Conditional
- Lethal
types of chemical changes
- Spontaneous chemical changes (depurination and deamination)
- Base analogs
- Pyrimidine dimers
