Lire 1815

Figure

Vitamin C is chemically similar to some 6-carbon monosaccharides.

deficiency of folacin leads to megaloblastic anemia, which is characterized by a reduced number of normal red blood cells and the presence of large, nucleated red cells. Folacin deficiency has been linked to neural tube defects, in which the tube that becomes the central nervous system in a fetus fails to close entirely. Neural tube defects include spina bifida and anencephaly. Taking synthetic folacin supplements just before and during pregnancy can greatly reduce the risk of a neural tube defect.

Naturally occurring folate is a mixture of compounds that have the same activity as synthetic folic acid, also called pteroylmonoglutamic acid. However, synthetic folic acid is much more stable and enters the bloodstream much more readily. This difference has led to confusion. For example, 200 micrograms of synthetic folic acid is prescribed to treat anemia, but the same effect requires 400 micrograms of folate from foods. Synthetic folic acid used to enrich grain foods has a greater effect on health than folate.

8. Biotin. Biotin is a simple compound that is stable to the effects of heat, acids, and light but may be destroyed by oxidation or bases. (See figure 18.16 for the molecular structure of biotin.)

Biotin is a coenzyme in metabolic pathways for amino acids and fatty acids. It also plays a role in the synthesis of the purine nitrogenous bases of nucleic acids.

Metabolically active organs such as the brain, liver, and kidneys store small quantities of biotin. Bacteria that inhabit the intestinal tract synthesize biotin. The vitamin is widely distributed in foods, and dietary deficiencies are rare. Good sources include liver, egg yolk, nuts, legumes, and mushrooms.

D Which biochemicals comprise the vitamin B complex?

9 Which foods are good sources of vitamin B complex?

NH2CO CH

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