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8.1 Alteration of sequence of bases in DNA can alter the structure of…
8.1 Alteration of sequence of bases in DNA can alter the structure of proteins
types of mutations
gene mutation
change in base sequence of DNA code e.g
base substitutions
base deletions/additions (frame shift)
(base inversions and translocations)
definitions
gene
a sequence of DNA bases that code for a sequence of amino acids in a polypeptide
mutation
change in base sequence or quantity of DNA
chromosome mutation
any change in the number of chromosomes
caused by non-disjunction (a failure of homologous chromosomes/chromatids to separate during meiosis)
polyploidy
a change in the number of sets of chromosomes e.g. some plants are 8n (8 sets of chromosomes)
aneuploidy
a change in the number of an individual chromosomes e.g. 3x chromosome 21 causes downsyndrome
types of gene mutation
base substitution
One nucleotide in a section of DNA is replaced by another with a different base. There is a change of base at this point in the genetic code.
base deletion
One or more bases are lost from the genetic code. Results in a frame shift mutation.
base addition
One or more bases are added to the genetic code. Results in a frame shift mutation.
base duplication
One or more bases end up being repeated in the genetic code. Results in a frame shift mutation.
base inversion
A sequence of bases get separated from the DNA then are inserted again but in the reverse order
base translocation
A group of bases are separated from the DNA sequence on one chromosome and inserted into the DNA sequence on another chromosome
why can a base substitution lead to a non-functional enzyme
Change in base sequence of DNA (one base triplet)
Change in base sequence of mRNA (one codon)
Change in primary structure of enzyme / amino acid sequence in polypeptide
Change in hydrogen/ionic/disulphide bonds formed
Change in tertiary structure of enzyme’s active site
Enzyme and substrate no longer complementary so substrate can no longer bind to active site / enzyme substrate complex cannot form
what is the difference between a substitution mutation to an addition mutation
base addition is a frame shift mutation
this results in a change in base sequence of DNA of all base triplets downstream of mutation (rather than change in one base triplet)