Explain the role of haemoglobin as a buffer
To pass this question, the candidate only needed to define a buffer (weakly ionised
acid or base in equilibrium with its full ionised salt), what it does, then discuss how
Haemoglobin functions in this capacity. In that regard, brief review of how CO2 is
buffered, the role of haemoglobin histidine residues, buffering capacity of oxy
haemoglobin and deoxy haemoglobin and how this contributes to the Haldane effect
would have rounded out a very good answer.
Additional credit was given for an understanding that histidine contains an imidazole
group and how these groups are effective as a buffer.
Few candidates mentioned that haemoglobin was quantitatively significant and no
candidate mentioned that it is the primary buffer for CO2. Many answers were quite
brief and did not explore the subject matter asked.
Syllabus: B1h, 2c, 2b and Section F
Recommended sources: Nunn’s Applied Respiratory Physiology, Lumb, page 228 to
230