Mutations

Question 1

What is a gene mutation?

Answer 1

1. A change in the base sequence of DNA (on chromosomes)
2. Can arise spontaneously during DNA replication (interphase)

Question 2

What is a mutagenic agent?

Answer 2

A factor that increases rate of gene mutation, eg. ultraviolet (UV) light or alpha particles.

Question 3

Explain how a mutation can lead to the production of a non-functional protein or enzyme:

Answer 3

1. Changes sequence of base triplets in DNA (in a gene) so changes sequence of codons on mRNA
2. So changes sequence of amino acids in the polypeptide
3. So changes position of hydrogen / ionic / disulphide bonds (between amino acids)
4. So changes protein tertiary structure (shape) of protein
5. Enzymes - active site changes shape so substrate can’t bind, enzyme-substrate complex can’t form

Question 4

Explain the possible effects of a substitution mutation:

Answer 4

1. DNA base / nucleotide (pair) replaced by a different base / nucleotide (pair)
2. This changes one triplet so changes one mRNA codon
3. So one amino acid in polypeptide changes,Tertiary structure may change if position of hydrogen / ionic /
   disulphide bonds change
   OR amino acid doesn’t change. Due to degenerate nature of genetic code (triplet could code for same amino acid) OR if mutation is in an intron so removed during splicing

Question 5

Explain the possible effects of a deletion mutation:

Answer 5

1. One nucleotide / base (pair) removed from DNA sequence
2. Changes sequence of DNA triplets from point of mutation (frameshift)
3. Changes sequence of mRNA codons after point of mutation
4. Changes sequence of amino acids in primary structure of polypeptide
5. Changes position of hydrogen / ionic / disulphide bonds in tertiary
   structure of protein
6. Changes tertiary structure / shape of protein