Question

1. [15 marks]

discuss the function of haemoglobin. In your answer include the roles of:

1. 2,3-BPG (2,3- bisphosphoglycerate)
2. carbon dioxide
3. protons

Answer 1

1.Haemoglobin is a allosteric, conjugated protein with four polypeptide chain joined by non covalent bond.It contains heme prosthetic group that's a iron containing porphyrin derivatives.The globin part consists of four polypeptide chain.

2.There are four main functions of the hamoglobin:-

(A)It facilitate oxygen transport :- About 98% of blood oxygen is bound to Hb in RBC.One Hb molecule binds with four molecules of oxygen to form oxyhemoglobin. it is a reversible reaction that is a oxygenation process not an oxidation. In Hb iron in Fe+² state binds with Hb not in Fe+³ state.

(B).It facilitate Co2 transport:- Co2 binds to Hb and form carbaminohemoglobin.It combine with amino groups of N- terminal amino acid of alpha chchaim and beta chain of globin.About 23% of carbon dioxide is transported by the Hb. The increase in concentration of co2 causes dissociation of oxyhemoglobin.

- BPG is present in the RBC of human beings ,In deoxygenated state Hb binds one molecule of BPG that forms salt bridge with the terminal amino group of both beta chain and stablises the Hb therefore reduce the oxygen affinity of Hb . An increase in concentration of BPG shift the graph to the right,causes more oxygen be liberated.

(C). It has an important role as a buffer that maintain the pH by combining with H+ ions to form hemoglobinic acid. The oxyhemoglobin also acts like a acid whose association and dissociation cause change in pH.

(D) It helps in transport of nitric oxide.