Question

Choose the correct option(s) with regard to haemoglobin (Hb)

• A. Hb binds oxygen in a co-operative process
• B. The metal ion in oxy-Hb has a larger size than that in deoxy-Hb
• C. Hb takes up more oxygen at pH 7.4 than at pH 6.8
• D. The metal ion is paramagnetic in deoxy-Hb

Hint:

Deoxy-Hb: high spin Fe$^{2+}$ → paramagneticOxy-Hb: low spin Fe$^{2+}$ → diamagneticAlso remember Bohr effect for pH dependence

Answer 1

The Correct Option is A, C, D

Step 1: Understand oxygen binding in Hb.
Haemoglobin shows cooperative bindingThis means binding of one O$_2$ molecule increases affinity for the nextThus, oxygen binding is not independent but cooperative

Step 2: Check statement (A).
Since Hb exhibits cooperative binding behaviour, statement (A) is correct

Step 3: Compare metal ion size in oxy and deoxy Hb.
In deoxy-Hb, Fe$^{2+}$ is high spin and has a larger ionic radiusUpon oxygenation, Fe$^{2+}$ becomes low spin and its size decreases

Step 4: Check statement (B).
Statement (B) says oxy-Hb has larger metal ion, which is incorrectActually, Fe$^{2+}$ becomes smaller in oxy-HbThus, (B) is incorrect

Step 5: Effect of pH (Bohr effect).
At higher pH (7.4), haemoglobin has higher affinity for oxygenAt lower pH (6.8), affinity decreases and oxygen release is favored

Step 6: Check statement (C).
Thus, Hb binds more oxygen at pH 7.4 than at pH 6.8So, (C) is correct

Step 7: Magnetic behaviour.
In deoxy-Hb, Fe$^{2+}$ is high spin with unpaired electrons → paramagneticIn oxy-Hb, electrons pair up → diamagnetic
Thus, (D) is correct
\[ \boxed{\text{(A), (C) and (D)}} \]