4.2.6 Nucleic Acid & Amino Acid Sequence Comparison

Impact of Mutations:

• A mutation in the base sequence of a gene can lead to a change in the sequence of amino acids in the resulting polypeptide.
• The effect of a mutation depends on the role of the altered amino acid in the structure and function of the protein.
• Degeneracy of the genetic code means that multiple codons can code for the same amino acid, so not all mutations result in changes to the protein.

Types of Mutations:

1. Substitution:

• Definition: When one nucleotide in the DNA sequence is replaced by another.
• Effects:
• May have no effect if the new codon codes for the same amino acid (due to the degenerate code).
• Can lead to a different amino acid being incorporated, potentially altering protein function.
• The impact depends on the importance of the affected amino acid in the protein's structure or active site.

2. Deletion:

• Definition: When a nucleotide is removed from the DNA sequence.
• Effects:
• Causes a frameshift mutation, altering the grouping of codons from the point of deletion onwards.
• Results in a completely different amino acid sequence, likely rendering the protein non-functional.
• Frameshift mutations are often more severe than substitutions.

Comparing Nucleic Acids and Amino Acids:

• Scientists compare DNA base sequences or the resulting amino acid sequences to study evolutionary relationships:
  • Closely related species have similar DNA sequences and produce similar proteins.
  • Over time, mutations accumulate, leading to differences in DNA and protein sequences, which can be used to track evolutionary divergence.