7-Dehydrocholesterol

7-Dehydrocholesterol is a zymosterol that is an intermediate in the biosynthesis of cholesterol. It is a precursor to vitamin D3 and is converted to this vitamin when skin is exposed to sunlight.

Structure and properties

7-Dehydrocholesterol is a sterol. It is similar in structure to cholesterol, but it has a double bond between the seventh and eighth carbon atoms in the B ring of the steroid structure. This double bond is what gives 7-dehydrocholesterol its name.

Biosynthesis

7-Dehydrocholesterol is synthesized from lanosterol in a series of reactions that involve the removal of three methyl groups, the reduction of a double bond, and the introduction of a double bond. The enzyme that introduces the double bond to form 7-dehydrocholesterol is 7-dehydrocholesterol reductase.

Role in vitamin D synthesis

When skin is exposed to ultraviolet B (UVB) radiation from the sun, 7-dehydrocholesterol in the skin is converted to previtamin D3. This is then converted to vitamin D3 (cholecalciferol) in a heat-dependent process. Vitamin D3 can be further metabolized to form the active form of vitamin D, calcitriol.

Clinical significance

Mutations in the gene that encodes 7-dehydrocholesterol reductase can lead to Smith-Lemli-Opitz syndrome, a genetic disorder characterized by intellectual disability and physical abnormalities. This is because these mutations result in a decrease in the production of cholesterol and an increase in the levels of 7-dehydrocholesterol.

See also

• Cholesterol
• Vitamin D
• Smith-Lemli-Opitz syndrome

7-Dehydrocholesterol Resources
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