We propose a novel dynamic subcarrier allocation (DSCA) design for dual-band orthogonal frequency division multiple access passive optical network (DB-OFDMA-PON), supporting integrated fronthaul and backhaul services, given their stringent requirements in emerging 5G networks. An optimization problem is formulated to maximize both the bandwidth utilization and QoS guarantees. The simulation results show that our proposed DSCA achieves the desired statistical multiplexing gain and high performance in terms of throughput and delay. Keywords: Backhaul, Dynamic subcarrier allocation, Fronthaul, Dual-band OFDMA, Passive optical network