Vitamin amino acids. Most vitamins are not single molecules, but groups of related molecules called vitamers. For example, vitamin E consists of four tocopherols and four tocotrienols. The thirteen vitamins required by human metabolism are: vitamin A (retinols and carotenoids), vitamin B (thiamine), vitamin B (riboflavin), vitamin B (niacin), vitamin B (pantothenic acid), vitamin B (pyridoxine), vitamin B (biotin), vitamin B (folic acid or folate), vitamin B (cobalamins), vitamin C (ascorbic acid), vitamin D (calciferols), vitamin E (tocopherols and tocotrienols), and vitamin K (quinones). Vitamins have diverse biochemical functions. Some forms of vitamin A function as regulators of cell and tissue
B2 (classification) guide runs on the right side of the runner. For races of or longer, a runner may use up to two guides, but the course officials must be informed of any decision to use more than one guide in advance of the race. In the marathon, the runner may use up to four different guides. The runner must finish ahead of the guide. In running, the guide attempts to match the running pattern of the runner, not the other way around. B2 (classification) B2 is a medical based Paralympic classification for blind sport. Competitors in this classification have vision that