Electronic – Can a transistor’s emitter and collector be used interchangeably

The first comprehensive logic series was the TTL series 74xx. This used BJTs (Bipolar Junction Transistors). Later there came variants like the often used 74LSxx, where the "LS" stands for Low-power Schottky TTL. As the name implies these used less power than the rather power-hungry TTL, and were faster too. At the same time the CMOS 4000 series was developed. The "C" in CMOS stands for Complementary, meaning it's a combination of N-channel and P-channel MOSFETs. Their construction is simpler than TTL and they use far less power. Later standard CMOS developed into HCMOS, "H" for High-speed. Most 74LSxx types have been released as HCMOS in the 74HCxx series, or the 74HCTxx series, which is TTL compatible. Later more variants were developed, like Advanced CMOS (74ACxx).

Microcontrollers are built in HCMOS technology, so they use MOSFETs. AFAIK JFETs aren't used for logic ICs. The transistor you show in the picture is a BJT, which you can tell from the pin designation:

E = Emitter
B = Base
C = Collector

For a MOSFET the pins would be

S = Source
G = Gate
D = Drain

respectively.

Many ICs in the 74HCxx series were originally released in 14 or 16 pin DIL packages, which meant that they would fit four 2-input gates. With miniaturization (SMT) came the demand for smaller packages, even if they contained less gates. Several manufacturers offer single-gate and dual-gate versions of logic gates. For example, NXP has a 74LVC1G00 (single 2-input NAND) and a 74LVC2G00 (dual 2-input NAND) version of the classical 74HC00. 74LVCxx is yet another HCMOS technology. This page lists all NXP logic families.

This circuit should work but I would make two serious recommendations.

1) Purge that 1N4148 diode and replace it with a Schottky type, such as a BAT54A, to get a much lower Vf.

2) What is the aversion to using a single logic gate part? Put in a single 2-input gate device to give you the ability to override the UART TTL output to generate the break condition.

If your project is a one-off type or hobby project you should be just fine with approach 1. On the other hand if you are making a commercial product I really recommend approach 2.