Gene mutation Flashcards
What is a gene mutation?
A change in the base sequence of DNA
Can arise spontaneously during DNA replication (interphase)
Involves base deletion / substitution
How can a mutation lead to the production of a non-functional protein / enzyme?
Change in base sequence of DNA
Changes sequence of codons on mRNA
Changes sequence of amino acids in the primary structure of the polypeptide
Changes position of hydrogen / ionic / disulphide bonds in tertiary structure of protein
Changes tertiary structure / shape of the protein (and active site if enzyme)
(if enzyme) substrate can’t bind to active site and form an enzyme-substrate complex
Explain how a base deletion can affect a protein.
One nucleotide removed from DNA sequence
Changes triplet sequence from the point of mutation (frameshift)
Changes sequence of codons on mRNA after point of mutation
Changes sequence of amino acids in primary structure of polypeptide
Changes position of hydrogen / ionic / disulphide bonds in tertiary structure of protein
Changes tertiary structure / shape of protein i.e. non-functional or new and superior protein
Explain how a base substitution can affect a protein.
Nucleotide in DNA replaced with another nucleotide
Change in one base → changes one triplet
Changes one mRNA codon and one amino acid → sequence of amino acids in primary structure of polypeptide changes
Due to the degenerate nature of the genetic code, the new triplet may still code for the same amino acid so the sequence of amino acids in the primary structure of the
polypeptide remains unchanged
Mutations in the number of chromosomes (chromosome non-disjunction)
Homologous chromosomes fail to separate during meiosis I OR sister chromatids fail to separate during meiosis II
One gamete has an extra copy of this chromosome and the other has none
Upon fertilisation, zygote has one fewer (dies) or one extra chromosome (survives)
Arises spontaneously
Causes genetic diseases e.g. down’s syndrome in humans – extra copy of chromosome 21
