  The latest experiments have confirmed the theoretically expected universal
value $\pi e^2/2h$ of the ac conductivity of graphene and have revealed
departures of the quasiparticle dynamics from predictions for the Dirac
fermions in idealized graphene. We present analytical expressions for the ac
conductivity in graphene which allow one to study how it is affected by
interactions, temperature, external magnetic field and the opening of a gap in
the quasiparticle spectrum. We show that the ac conductivity of graphene does
not necessarily give a metrologically accurate value of the von Klitzing
constant $h/e^2$, because it is depleted by the electron-phonon interaction. In
a weak magnetic field the ac conductivity oscillates around the universal value
and the Drude peak evolves into a peak at the cyclotron frequency.
