Mutation and Mutagenesis 1 Flashcards
What is mutation?
A change in the nucleotide sequence of a gene which can lead to a mutant protein and may affect control of a gene
How are mutations passed on
Mutations are inheritable only if the reproductive cells DNA is affected
What is polymorphism? and give an example
A nondisadvantages mutation becoming established in a population - ie more than one allele existing.
Example - the genes that control hair colour are polymorphic
Mutation Rate
rate at which DNA sequences change.
Two ways of measuring mutation rate
1) Indirectly estimated - comparing the amino acid sequence of the same protein in several different species and compare with time of divergance from a common ancestor.
2) Observe rate at which spontaneous changes arise in the genome ofgrowing cells.
Different types of mutation
1) Point mutations
2) Multisite mutations
Point mutations
1) Transition: changes a pyrimidine to a pyrimidine (T to C or C to T)
2) Transversion: Change a pyrimidine to a purine or vice-versa.
3) Insertion of a base
4) Deletion of a base
Transitions or transversion can cause 3 effects on codons:
Same-sense mutations: changes the codon for another that produces the same amino acid (causes no effect)
Missense mutation - change a codon that codes for a different amino acids (may vary depending on how similar the amino acid is to the original. Also depends on the role aa has on secondary and tertiary structure) eg cysteine is usually crucial
Nonsense mutation - changes codon to a termination codon (causes premature termination of translation leading to loss of function unless at carboxy terminal)
What effects can insertion and deletion cause
Both lead to a frame shift which will displace thereading frame leading to an alteration of all subsequent amino acids
This produces a protein that is normal functionless.
Frameshift mutations (2 types)
Changes effect more than one base
1) Deletions - one or more nucleotides are removed from the sequence. If three are removed a full amino acid is missing from the sequence. If only one or two are removed it could change the entire sequence following.
2) Insertions - when one or more nucleotides are inserted into the sequences, If 3 are inserted at once an extra amino acid would be coded for, for one or two again the entire sequence changes.
What are Transposons
are DNA sequences that can jump from one location on the genome to another.
Causes of mutations
1) Spontaneous mutations - a random event, not common due to the DNA’s ‘proof’ reading ability
2) Induced mutations - Chemicals, ionizing radiation
DNA repair mechanisms
1) DNA polymerase - corrects mismatched base pairs
2) Photolyase - splits UV light induced thymine dimers.
3) DNA methyl transferase removes the methyl group changing a base back to its original form.
4) Glycosylase removes alkylated or foreign bases by cleaving nucleoside bonds between deoxtribose sugar and base.
