Gene Mutation Flashcards
Germ-line mutations
mutations passed through the gametes
Somatic Cell Mutations
Show patches of affected areas, no gametes will carry the mutations.
Spontaneous Mutations
Occur naturally. A baby will have an average of 60 new mutations, 90% will be in non-coding regions
What percentage of DNA actually codes for proteins?
1.5%
What are induced mutations caused by?
Mutagens
Chromosomal mutation effects can result in:
Duplications
Inversions
Deletions
Insertions
Translocation
Mutations in nucleotide sequences include:
point mutations
base substitutions
insertions
deletions
A point mutation is:
A substitution of a single base nucleotide with another nucleotide (doesn’t effect the number of nucleotides)
Silent Mutation
Does not change the amino acid encoded by the codon and includes mutations occuring in introns.
Missense mutations
Changes the amino acid encoded by the codon.
Why would a missense mutation be harmless?
If the amino acid that the changed codon produces is chemically similar to the one the non-mutated gene codes for, or if it is in an unimportant area.
Why would a missense mutation be harmful?
A chemically different amino acid can cause changes in structure and function, such as in sickle cell anaemia in which the change from Glu to Valine results in a structural change in the RBS that effects its function.
Nonsense Mutation
Changes an amino acid codon to a termination (stop codon). the resulting amino acid is shortened.
Sense Mutations
Converts a stop codon to a sense codon.
What causes a Frameshift Mutation?
Insertions or deletions of a single base pair.
Loss of Function mutation.
A mutational effect that impedes function.
Mostly recessive, but can be dominant.
Null Mutations
a mutational effect that abrogates/blocks function.
Trinucleotide Repeat Diseases
Genetic diseases characterised by the presence of unstable and abnormal expansions of DNA-triplets.
abnormally repeated DNA-triplets may cause:
gene inactivation or production of a toxic protein may be caused by:
Genetic Anticipation
Severity of mutation increases with each successive generation.
Cystic Fibrosis is what type of disease?
A Trinucleotide Repeat Disease
Lethal mutations can be carried on to successive generations by…
slow onset.
Mutations such as trinucleotide repeat diseases can increase in severity with each successive generation due to:
genetic anticipation.
Cystic Fibrosis is cause by what a mutation of which gene?
The CFTR gene.
What is the function of the protein coded for on the CFTR gene?
It is an ion channel for fluid homeostasis and when mutated, causes a build up of fluid in the lungs.
The position of the mutation in the CFTR gene effects what?
Gene phenotype and severity of protein function. Can be partially active or completely inactive - which affects drug function.
Mutagens
A physical or chemical agent that changes the DNA of an organism and increases the frequency of mutations.
What mutagens can cause chemical modifications to DNA in the intracellular environment?
Free radicals and Reactive Oxygen Species
How do free radicals and reactive oxygen species chemically modify DNA?
Can cause loss of bases and single strand breaks by oxidising the nucleotides and thus affecting their chemical structure. (steals their electrons)
What are some examples of mutagens from the external environment?
Radiation
Chemicals
Base Analogues
Base Modifiers
How does ionising radiation cause DNA mutations?
Ionising radiation causes the formation of free radicals and reactive oxygen species that oxidises nucleotides.
How does non-ionising radiation (such as UVB) cause DNA mutations?
The biological effects observed for non-ionising radiation includes production of free radicals, double stranded DNA breaks and induced thymine dimers.
How do chemical mutagens cause DNA mutations?
They intercalate between base pairs of DNA and causes separation of base pairs and unwinding. They make good nucleic acid stains.
Base analogues have a similar structure to…
nucleotide bases and are incorporated into the DNA.
How do Base Analogue mutagens cause mutations?
They can cause mispairing during DNA replication.
Two types of Base Modifiers are:
Alkylating Agents
Mustard gas
Alkylating agents act as mutagens by:
transferring alkyl groups (methyl/ethyl) to nucleotide bases.
What does Mustard Gas do to Guanine?
It akylates guanine leading to cellular death and cancer.
