Which starting substance is used to initiate the biosynthesis of steroid hormones?

Which starting substance is used to initiate the biosynthesis of steroid hormones?

• A. Cholesterol
• B. Cortisol
• C. Catecholamines
• D. Progesterone

Answer: (A)

Steroid hormones all originate from cholesterol, which serves as the starting substrate for their biosynthesis. Cholesterol is transported into mitochondria where it undergoes side-chain cleavage to form pregnenolone, the first steroid in the pathway. From there, a series of enzymatic steps converts pregnenolone into progesterone and then into the various steroid hormones such as cortisol, aldosterone, and the sex steroids. This makes cholesterol the foundational material for initiating steroidogenesis. Cortisol is produced downstream from cholesterol, not the starting substance. Catecholamines come from tyrosine through a different biochemical pathway and are not steroids. Progesterone is an intermediate product further along the pathway, not the initial substrate that starts the cascade.

Steroid hormones all originate from cholesterol, which serves as the starting substrate for their biosynthesis. Cholesterol is transported into mitochondria where it undergoes side-chain cleavage to form pregnenolone, the first steroid in the pathway. From there, a series of enzymatic steps converts pregnenolone into progesterone and then into the various steroid hormones such as cortisol, aldosterone, and the sex steroids. This makes cholesterol the foundational material for initiating steroidogenesis.

Cortisol is produced downstream from cholesterol, not the starting substance. Catecholamines come from tyrosine through a different biochemical pathway and are not steroids. Progesterone is an intermediate product further along the pathway, not the initial substrate that starts the cascade.