Cognitive Radio Networks (CRN) have enabled us to efficiently reuse the underutilized radio spectrum. The MAC protocol in CRN defines the spectrum usage by sharing the channels efficiently among users. In this paper we propose a novel TDMA based MAC protocol with dynamically allocated slots. Most of the MAC protocols proposed in the literature employ Common Control Channel (CCC) to manage the resources among Cognitive Radio (CR) users. Control channel saturation in case of large number of CR users is one of the main drawbacks of the CCC based MAC protocols. In contrast with CCC based MAC protocols, DSAT-MAC protocol is based on the TDMA mechanism, without using any CCC for control information exchange. The channels are divided into time slots and CR users send their control or data packets over their designated slot. The protocol ensures that no slot is left vacant. This guarantees full use of the available spectrum. The protocol includes the provision for Quality of Service, where real-time and safety critical data is transmitted with highest priority and least delay. The protocol also ensures a fair sharing of available spectrum among the CR users, with the mechanism to regulate the transmission of malicious nodes. Energy saving techniques are also presented for longer life of battery operated CR nodes. Theoretical analysis and simulations over ns-2 of the proposed protocol reveal that the protocol performs better in various CR adhoc network applications.