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 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, which is Pro (Proline), is ACU.

A change in the sequence of DNA base triplets is referred to as a gene mutation.

A change in the sequence of DNA base triplets can alter the amino acid sequence of the protein. For instance, a mutation from CTC to CAC leads to a change in the codon on the mRNA from GAG to GUG. This results in a changed amino acid sequence where Val is substituted for Glu. Consequently, haemoglobin S is formed, which cannot carry oxygen as efficiently as normal haemoglobin. This mutation can create a protein that is structurally different and less functional due to the altered amino acid sequence.

A person with haemoglobin S may experience reduced oxygen supply to their tissues, leading to symptoms such as fatigue and anaemia. This condition can also cause complications like pain episodes due to sickle cell crises as the abnormal haemoglobin leads to distortion of red blood cells.