The term "vitamin" is derived from the Latin word vita meaning life, and describes a class of nutrients that regulate important metabolic reactions. Collectively, vitamins assist in the formation of a wide spectrum of biochemicals including hormones, enzymes, proteins, neurotransmitters, and the genetic materials RNA and DNA. Although these organic nutrients are generally not structurally related to each other, they all promote metabolic balance within cells, ensuring that important biochemical reactions proceed as required. Many vitamins combine with proteins to create enzymes (termed co-enzymes) that mediate chemical reactions occurring within the body. Vitamins are divided into two categories, one of which is commonly known as fat soluble and includes vitamins A, D, E, and K. The other, water soluble, vitamin category includes the B-vitamin complex and vitamin C. Both of these vitamins must frequently be replenished because they are not stored in body tissue, and are usually rapidly excreted with urine. Vitamin C, or ascorbic acid, is necessary for a wide range of biochemical reactions and its antioxidant properties are vital to several key metabolic pathways.