what is a gene mutation?
a change in the base sequence of DNA
it can arise spontaneously during DNA replication
what is a mutagenic agent?
a factor that increases rate of mutation eg UV light or alpha particles
what are the 6 types of gene mutation?
substitution, addition, deletion, duplication, inversion, translocation
what is substitution?
a base/ nucleotide is replaced by a different base/ nucleotide in DNA
what is duplication?
a sequence of DNA bases/ nucleotides is replicated/ copied
what is addition/ deletion?
1 or more bases/ nucleotides are added/ removed from DNA base sequence
what is inversion?
a sequence of bases/ nucleotides detaches from the DNA sequence, and then rejoins at the same position in the reverse order
what is translocation?
a sequence of DNA bases/ nucleotides detaches and is inserted at a different location within the same or different chromosome
how can a gene mutation lead to the production of a non-functional protein or enzyme? (5)
- changes sequence of base triplets in DNA so changes sequence of codons on mRNA
- so changes sequence of amino acids in the encoded polypeptide
- so changes position of hydrogen/ ionic/ disulphide bridges between amino acids in tertiary structure
- so changes tertiary structure of protein
- for enzymes- active site changes shape so substrate can’t bind as not complementary, ES complex can’t form
why do not all gene mutations affect the order of amino acids?
some substitutions only change 1 triplet code/ codon which could still code for the same amino acid as the genetic code is degenerate (an amino acid can be coded for by more than one triplet)
some occur in introns which do not code for amino acids as they are removed during splicing
why is a change in amino acid sequence not always harmful?
may not change the tertiary structure of protein (if position of bonds don’t change)
OR may positively change the properties of a protein which gives the organism a selective advantage
what is a frameshift?
when mutation (addition, deletion, duplication or translocation) changes the number of nucleotides/ bases by a number not divisible by 3
this sifts the way the genetic code is read, so all the DNA triplets/ mRNA codons downstream from the mutation point change (so significant effects)
what are the 2 ways mutations can lead to production of a shorter polypeptide?
- deletion or translocation- triplets/codons missing so amino acids missing
- substitution, addition, deletion, duplication, inversion or translocation- premature stop codon so end of polypeptide production
what are the 3 ways a mutagenic agent can increase the rate of mutations?
- acting as a base
- altering bases
- changing structure of DNA (causes problems during DNA replication)
