TTL NOR Gate analysis
In TTL logic, the input transistor works in a manner similar to the two diodes in your DTL inverter. If the input, (emitter) is high, current will flow from the base through the collector. If the emitter is low, current will not flow out of the collector. Unlike most uses of a transistor, this use in not particularly related to amplification. It replaced the double diodes in DTL logic because it switches faster.