Ferritin is a spherical protein used to store and regulate iron levels within living cells. It consists of a protective protein shell surrounding a hollow inner cavity where iron Fe3+\text{Fe}^{3+}Fe3+ ions are safely deposited.
A specific bacterial ferritin molecule has a hollow inner cavity with a total volume of 250 nm3250\text{ nm}^3250 nm3.
This inner cavity can hold a maximum of 4000 Fe3+4000\text{ }\text{Fe}^{3+}4000 Fe3+ ions.
The volume of a single Fe3+\text{Fe}^{3+}Fe3+ ion is 9.50×10−4 nm39.50 \times 10^{-4}\text{ nm}^39.50×10−4 nm3.
Calculate the volume of the inner cavity that is not occupied by Fe3+\text{Fe}^{3+}Fe3+ ions.
Explain how hydrophilic and hydrophobic interactions of the amino acid R-groups stabilize the spherical shell structure of this protein.
