Question

Background info: Leishmania is a parasite that causes a disfiguring infection that is treated by antimony. Antimony works because the parasites have a transporter protein that imports the chemical into parasite cells. Doctors found that many infections had become resistant to antimony, the standard treatment for this infection.When they sequenced the genomes of Leishmania from treatment-resistant Leishmania, scientists found that the gene encoding the protein transporter contained two inserted nucleotides.

Question: One patient asks whether the same effect could have been produced by the insertion of three nucleotides. What would be your response?

Answer 1

the genes encode for proteins. Gene is a part of DNA that contains nucleotides as monomers. While proteins are polymers of amino acids. 3 nucleotides of a gene constitute a codon that codes for an amino acid in a protein. The genetic code is non-overlapping and commaless, i.e, all the nucleotides are read by translation machinery as 3 nucleotide fragments and one amino acid for each 3 nucleotide segment and no nucleotides are missed by translation machinery.

Hence, when or 1 or 2 nucleotides are inserted in a gene, the whole amino acid chain (or protein) from the site of insertion would change. However, when 3 (or multiples of 3) nucleotides are inserted into a gene, one extra amino acid would be incorporated in the middle of the amino acid chain leaving the rest of the protein sequence normal. the incorporation of one amino acid would have minimal impact on the protein structure and function compared to a complete change in the amino acid sequence.

same effect could not have been produced by the insertion of three nucleotides.