Explain the causes and consequences of sickle cell anaemia (5)

Sickle cell anaemia is caused by a point mutation, exchanging adenine for thymine in the DNA codon CTC. This causes a change in the mRNA to GUG, which results in a change in the polypeptide sequence during protein synthesis. Glutamic acid is substituted by a valine as the sixth amino acid in the protein haemoglobin. The change in tertiary structure of haemoglobin means that red blood cells become curved. These sickle-shaped cells are able to transport less oxygen from the lungs to respiring tissues, and they can get stuck in narrow blood vessels, resulting in a sickle cell crisis. This mutation also confers resistance to malaria.