mutations + variation

Question 1

what is a gene mutation

Answer 1

• change in base sequence of dna
• can arise spontaneously during replication - interphas
• involves base deletion + substitution

Question 2

How can a mutation lead to the production of a non-functional protein / enzyme?

Answer 2

Change in base / triplet sequence of DNA / gene
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

Question 3

explain how base deletion can affect a protein

Answer 3

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

Question 4

Explain how a base substitution can affect a protein. 1

Answer 4

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 etc.

Question 5

Explain how a base substitution can affect a protein. 2

Answer 5

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

Question 6

Explain how a base substitution can affect a protein. 3

Answer 6

if change in one base changes the amino acid codon to a stop codon then no more amino acids are joined on and so a dysfunctional protein results.

Question 7

what is a mutagenic agent

Answer 7

• Anything that increases the rate of gene mutation (above the rate of naturally occurring mutations)
• E.g. ultraviolet light or alpha particles or carcinogens