1.1. State the main role of the protein haemoglobin. 

1.2. In the hereditary disease sickle cell anaemia, a mutation results in the amino acid valine (which is non-polar) replacing glutamic acid (which is polar), making haemoglobin less soluble. Molecules of sickle-cell haemoglobin do not bind well to oxygen.

Explain why a sickle cell patient’s haemoglobin is less soluble than a non-sufferer’s haemoglobin. 

1.3. Each haemoglobin molecule can bind 4 oxygen molecules. There are 300 million haemoglobin molecules in each red blood cell. An adult human is estimated to have 3 x 10¹³ red blood cells in circulation at any one time. 

Calculate the theoretical maximum number of oxygen molecules that could be carried in the red blood cells of an adult human. 

1.4. Figure 1 below shows the structure of collagen protein at various levels of detail. 

Figure 1

Use Figure 1 to identify two features of collagen that make it a strong, structural protein.