what is a substitution mutation?
- gene mutation
- one nucleotide is incorrectly swapped during DNA replication for another nucleotide
- the correct nucleotide is replaced with an alternative nucleotide
- effects are small
what is a deletion mutation?
- gene mutation
- a nucleotide is skipped or absent from the replicated strand
- causes frameshift
- effects can be damaging
what is an insertion mutation?
- gene mutation
- an extra nucleotide is incorporated into the DNA sequence during replication
what is a gene mutation?
a change in the base sequence of chromosomes in the DNA
when are gene mutations likely to occur?
during S phase
DNA replication
what factors increase/decrease the rate of mutations?
- mutagenic agents
eg x rays
what is a non sense mutation?
translation stops before expected
what is a missense mutation?
- change to a singular amino acid
- can change the protein shape
why do deletions/insertions have bigger effects than substitution mutations?
- results in a frame-shift that changes the reading of subsequent codons
- alters the entire amino acid sequence that follows the mutation
- bigger effect on primary polypeptide as amino acids are incorrectly coded for
- impact upon the way the rest of the sequence is read by the cell
what is a point mutation?
changes to a single nucleotide
- either inserted, substituted or deleted
evaluate whether a base deletion mutation has a bigger effect on polypeptide structure than a base substitution mutation
- sub can result in silent mutation and no change to primary structure
- sub only changes a single amino acid
- sub does not change number of amino acids whereas deletion reduces by 3
- deletions are frame shift mutation, every amino acid downstream of mutation changes
- however sub can change codon to a stop and if this occurs near the start of the sequence, impact is significant
what is a frameshift mutation?
- complete change to the entire amino acid sequence of a protein after the mutation site
- because of the way the translated mRNA is read by the ribosomes
- mRNA is read in codons, groups of 3 nucleotides. If an additional 1 or 2 nucleotides are added or removed, the sequence is ‘shifted’
- translation machinery cannot know that there has been an error, and still reads the sequence in triplet codons
- the entire mRNA and resulting protein are completely different.
what makes a mutation more likely?
mutagenic agents
- high energy radiation (UV)
- ionisation (X ray)
- chemicals
why can substitution mutations be silent?
genetic code is degenerate
