What is the function of folic acid? A 44-year-old woman presents with extreme fatigue that has worsened over the past two month. She recently overcame her battle against alcoholism, and says her next goal is to improve her “horrible diet.” Physical examination is unremarkable. Laboratory studies are significant for a hemoglobin level of 8 g/dL and a mean corpuscular volume of 110 mm³. A folic acid deficiency is suspected.

Transfers one carbon intermediates between biochemical reactions

The correct answer is E. Folic acid plays a key role as a coenzyme for one-carbon transfer as seen in methylation reactions and is essential for the biosynthesis of purines and the pyrimidine thymidine. Deficiency of the vitamin is characterized by growth failure in children and macrocytic megaloblastic anemia. The anemia is a result of diminished DNA synthesis in erythropoietic stem cells. Large cells are seen with mean cell volumes of 100150 mm3 and reduced levels of hemoglobin. Folic acid is a water-soluble vitamin stored in small amounts by the body; thus a continuous supply is need from foods such as green, leafy vegetables, lima beans, and whole grain cereals. Nutrient defi - ciency can commonly lead to folate deficiency. The deficiency is usually seen in pregnant women and alcoholics Answer A is incorrect. Vitamin K serves as a coenzyme in the -carboxylation of glutamic acid residues in blood clotting proteins. A vita min K deficiency is rarely seen because adequate amounts are generally produced by intestinal bacteria or easily obtained from the diet. Decreased bacterial production in the gut (as with antibiotics, for example) can lead to hypoprothrombinemia and, subsequently, hemorrhage. Newborns have sterile intestines and cannot initially synthesize vitamin K. Because human milk fails to provide the adequate daily requirement of vitamin K, it is recommended that all newborns receive a single dose of vitamin K as prophylaxis against hemorrhagic diseases Answer B is incorrect. Ascorbic acid (vitamin C) acts as a coenzyme in hydroxylation of prolyl- and lysyl- residues of collagen, allowing collagen fibers to crosslink and providing greater tensile strength to the assembled fiber. A deficiency of ascorbic acid results in scurvy, a disease characterized by sore, spongy gums, loose teeth, fragile blood vessels, swollen joints, anemia, and poor wound healing Answer C is incorrect. 1,25-Dihydroxycholecalciferol, the active molecule of vitamin D, produces its effect at the DNA level to produce proteins in intestinal cells that allow for greater calcium and phosphate absorption. Vitamin D deficiency causes a net demineralization of bone, resulting in rickets in children and osteomalacia in adults. Rickets is characterized by continuous formation of collagen matrix of bone but incomplete mineralization, resulting in soft, pliable bones. In osteomalacia, demineralization of preexisting bones increases their susceptibility to fracture Answer D is incorrect. Vitamin A (retinol) is a component of the visual pigments of rod and cone cells. This fat-soluble vitamin plays an essential role in vision, growth, maintenance of epithelial cells, and reproduction. Night blindness is one of the earliest signs of vitamin A deficiency as a result of a loss in the number of visual cells. Further deficiency can lead to dryness of conjunctiva and cornea, leading to corneal ulceration and ultimately blindness.