Biochemistry : Steroid Hormone Pathways
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Example Question #11 : Steroid Hormone Pathways
The conversion of 25-hydroxycholecalciferol to the active vitamin D form of 1,25-dihydroxycholecalciferol occurs where?
Proximal tubule of the kidney
Intestinal goblet cells
Myocytes of the heart
Hepatocytes of the liver
Squamous cells of the skin
Proximal tubule of the kidney
The steroid conversion pathway of vitamin D begins in the skin where cholecalciferol is synthesized by UV light. In the liver a hydroxyl group is added making 25-hydroxycholecalciferol. In the proximal tubule of the kidney, another hydroxyl group is added, forming the active form of vitamin D - 1,25-dihydroxycholecalciferol.
Example Question #12 : Steroid Hormone Pathways
Glucocorticoids achieve their effects in cells by ____________.
binding to receptor tyrosine kinases on the plasma membrane, which phosphorylate other proteins leading to a cascading signal that changes gene expression
binding to heterotrimeric G proteins on the plasma membrane, leading to the synthesis of cAMP and a cascading signal that changes gene expression
spontaneously passing through the plasma membrane and forming a complex with a steroid receptor, which enters the nucleus and acts as a transcription factor
spontaneously passing through the plasma membrane and binding to transcortin, which allows them to enter the nucleus and act as a transcription factor
spontaneously passing through the plasma membrane and binding to albumin, which allows them to enter the nucleus and act as a transcription factor
spontaneously passing through the plasma membrane and forming a complex with a steroid receptor, which enters the nucleus and acts as a transcription factor
The correct answer is "spontaneously passing through the plasma membrane and forming a complex with a steroid receptor, which enters the nucleus and acts as a transcription factor." Glucocorticoids are steroid hormones, which are hydrophobic and thus can pass right through lipid membranes without having to interact with receptors in the plasma membrane. Transcortin and albumin are used to transport steroid hormones through the blood, but they do not enter the cell along with the hormone.
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