Question

how the following factors can affect the 3D shape of haemoglobin and its activity, Temperature, pH and Number of oxygen molecules bound?

Answer 1

Temperature:
I'm not quite sure about temperature, but I would say that the most logic thing would be that the hemoglobin affinity to oxygen increases with increasing temperature.

pH:
The oxygen affinity of hemoglobin decreases as pH decreases from a value of about 7.4. But this is a good thing however. As hemoglobin moves into a region of lower pH, its tendency to release oxygen increases. Only about 66% of the oxygen would be released in the absence of any change in pH if we go from the lungs to a active muscle. The chemical basis for this is that some of the charged amino acids changes so that there are made hydrogen bonding and electrostatic interactions. The formation of theses hydrogen bonding and electrostatic interactions stabilizes the T state, leading to a greater tendency for oxygen to be released.

Number of oxygen:
Hemoglobin undergoes substantial changes in quaternary structure on oxygen binding. The α1β1 and α2β2 dimers rotate about 15 degrees with respect to one another. The dimers themself are relatively unchanged, but there are localized conformational shifts. Thus, the interface between the α1β1 and α2β2 dimers is most affected by this structural transition. The α1β1 and α2β2 dimers are freer to move with respect to one another in the oxygenated state than they are in the deoxygenated state.
We often like to think of the deoxy form of hemoglobin (deoxyhemoglobin) for T state, while the fully oxygenated form (oxyhemoglobin) for R state.
Now in the R state, the oxygen-binding sites are free of strain and are capable of binding oxygen with higher affinity than are the sites in the T state.
So to sum up:
By triggering the shift of hemoglobin tetramer from the T state to the R state, the binding of oxygen to one site increases the binding affinity of other sites.

Answer 2

thanks :)