Final answer:
The coenzyme that must be obtained from the diet in addition to niacin is vitamin B12, as it is essential for many cellular processes including DNA synthesis and brain function, and cannot be synthesized by the human body.
Step-by-step explanation:
Two specific coenzymes we need to obtain from our diet are niacin and vitamin B12, as our bodies cannot synthesize them. Niacin, also known as vitamin B3, and vitamin B12 are both part of the B complex vitamins, playing vital roles in cellular metabolism. Vitamin B12 is particularly important because of its role in DNA synthesis and its involvement in the metabolism of every cell of the human body, especially affecting DNA synthesis and regulation, as well as fatty acid synthesis and energy production. We primarily rely on animal products such as liver, eggs, meat, and fish to obtain vitamin B12 because plants do not provide it. Hence, those on a vegan diet must seek fortified foods or supplements. Moreover, vitamin B12 is also essential for the proper function of the brain and nervous system, and its deficiency can lead to serious health issues like megaloblastic anemia.