Identify the sequence of sickle cell haemoglobin.

-Val-His-Leu-Thr-Pro-Val-Glu-Lys-

The correct answer is option 2. -Val-His-Leu-Thr-Pro-Val-Glu-Lys-.

Sickle cell hemoglobin (HbS) is a variant of hemoglobin where there is a specific mutation in the beta chain of the hemoglobin molecule. In normal adult hemoglobin (HbA), the sixth amino acid in the beta chain is glutamic acid (Glu). However, in sickle cell hemoglobin (HbS), there is a point mutation where glutamic acid is replaced by valine (Val) due to a single nucleotide substitution (GAG to GTG mutation) in the gene encoding the beta globin chain.

The sequence provided in the correct option, -Val-His-Leu-Thr-Pro-Val-Glu-Lys-, reflects this mutation: Val (Valine) replaces Glu (Glutamic acid) at the sixth position.

This single amino acid substitution from glutamic acid to valine alters the properties of the hemoglobin molecule. HbS tends to polymerize under conditions of low oxygen tension, leading to the characteristic sickling of red blood cells in individuals with sickle cell disease. This abnormal polymerization is responsible for the clinical manifestations of sickle cell disease, including the shape change of red blood cells, which can cause blockages in blood vessels and lead to severe pain crises and other complications.

Therefore, the sequence -Val-His-Leu-Thr-Pro-Val-Glu-Lys- accurately represents the beta chain sequence of sickle cell hemoglobin (HbS), where the amino acid substitution at the sixth position is crucial in understanding the pathophysiology of sickle cell disease.