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Genetics and evolution

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Question 38

A section of mRNA coding for a functional polypeptide is shown below:

mRNA: 5'- AUG - AGC - AAG - AAG - 3'

A point mutation occurred in the template DNA strand, resulting in the third mRNA codon changing from AAG (lysine) to AUG (methionine).

The genetic code lookup for the relevant codons is as follows:

  • AUG codes for Methionine
  • AGC codes for Serine
  • AAG codes for Lysine
  • AAA codes for Lysine
a.

(i) Name the type of covalent bond present in the primary structure of a protein that links successive amino acids.

[1]
b.

(ii) Outline the role of RNA polymerase in the synthesis of this mRNA molecule.

[2]
c.

(i) State the base sequence of the anticodon on the tRNA molecule that pairs with the mutated codon AUG.

[1]
d.

(ii) Explain how a mutation that changes the third codon from AAG to AAA would affect the final tertiary structure of the protein. Refer to the degeneracy of the genetic code.

[2]
e.

(iii) In contrast, a mutation changing AAG to AUG replaces lysine (hydrophilic) with methionine (hydrophobic). Explain how this substitution can alter the tertiary structure and biological activity of the protein.

[2]

Genetics and evolution Questions

  1. A Level
  2. /Biology
  3. /Genetics and evolution