2.1.1 Give the: (a) DNA base triplet for amino acid 3 (b) mRNA codon for amino acid 4 2.1.2 What is a change in the sequence of DNA base triplets called? 2.1.3 Use the information in the tables to explain how a change in the sequence of the DNA base triplets results in the formation of haemoglobin S, rather than normal haemoglobin - NSC Life Sciences - Question 2 - 2021 - Paper 2

The mRNA codon for amino acid 4 is ACU.

This change is referred to as a gene mutation.

In the formation of haemoglobin S, there is a change in the DNA sequence from CTC to CAC. This alteration leads to changes in the corresponding mRNA and transfer RNA (tRNA) sequences, resulting in the incorrect amino acid being incorporated into the beta chain of haemoglobin. Specifically, the codon for the wild-type hemoglobin (GAG) changes to GUG, which encodes for valine instead of glutamic acid. This single amino acid change significantly alters the properties of the hemoglobin, causing it to carry oxygen less efficiently.

A person with haemoglobin S would experience reduced oxygen transport in their blood. This can lead to symptoms such as fatigue and anemia due to the body's cells not receiving enough oxygen. Additionally, the sickled shape of the red blood cells can cause blockages in blood vessels, leading to painful crises and other health complications.