Graphene has two atoms per unit cell with quasiparticles exhibiting the Dirac-like behavior. These properties lead to interband in addition to intraband optical transitions and modify the $f$-sum rule on the longitudinal conductivity. The expected dependence of the corresponding spectral weight on the applied gate voltage $V_g$ in a field effect graphene transistor is $\sim {const}- |V_g|^{3/2}$. For $V_g =0$, its temperature dependence is $T^3$ rather than the usual $T^2$. For the Hall conductivity, the corresponding spectral weight is determined by the Hall frequency $��_H$ which is linear in the carrier imbalance density $��$, and hence proportional to $V_g$, and is different from the cyclotron frequency for Dirac quasiparticles.

16 pages, RevTeX4, 4 EPS figures; v2: to match PRB version