Figure 1. Chromosomes 16 and 11, the globin gene clusters and the respective chains. The genes are arranged (from 5¢ to 3¢) according to the timing of their activation. Green sections represent translated sequences (exons) and red sections denote intervening sequences (introns). Blue sections correspond to the untranslated 5¢ and 3¢ sequences flanking the globin genes. Combinations of the chains produced result in the various types of haemoglobins described in the text. Adapted from Weatherall (1991).

Figure 2. Primary structure of the and globin chains. Helical sections are labelled with capital letters; the sections between the helices are labelled with the letters of the flanking helices. NA denotes the N-terminal and HC the C-terminal section. From Weatherall and Clegg (1981).

Figure 3. Secondary structure of the human globin chain. The haem pocket is formed between histidine 92 (proximal) and histidine 63 (distal). Adapted from Weatherall and Clegg (1981).

Figure 4. Tertiary structure of the globin chain. The tetrapyrrolic flat haem ring lies between histidine F8 and histidine E7; the central dot corresponds to the iron molecule. Adapted from Weatherall and Clegg (1981).

Figure 5. Schematic presentation of the complete haemoglobin molecule (quaternary structure). The red rectangles denote the haem rings. Adapted from Alberts et al. (1997).

Figure 6. Oxygen dissociation curve of normal human haemoglobin (B) in comparison to the curve of haemoglobin with high oxygen affinity (A) and with low oxygen affinity (C). The normal dissociation curve shifts slightly to the left when blood pH increases and when temperature and the concentration of 2,3-diphosphoglycerate (2,3-DPG) decrease. The opposite deviation occurs when pH decreases or temperature and 2,3-DPG concentration increase.