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Questions and Answers
What is the biochemical significance of cholesterol?
What is the biochemical significance of cholesterol?
- It is the main cause of heart disease and atherosclerosis.
- It is only associated with atherosclerosis and has no other biochemical significance.
- It is the precursor of important steroids including bile acids, adrenocortical hormones, sex hormones, and vitamin D. (correct)
- It is a byproduct of steroid metabolism.
Which of the following carbon positions is NOT found in the steroid nucleus as part of the cyclopentanoperhydrophenanthrine structure?
Which of the following carbon positions is NOT found in the steroid nucleus as part of the cyclopentanoperhydrophenanthrine structure?
- C10
- C13
- C22 (correct)
- C18
What is indicated by the Δ (Delta) symbol in the context of steroid biochemistry?
What is indicated by the Δ (Delta) symbol in the context of steroid biochemistry?
- A triple bond between carbon atoms
- A double bond between carbon atoms (correct)
- A methyl group at the specified carbon position
- An α-bond in the hormone plane
How are β-bonds distinguished in the structure of a steroid?
How are β-bonds distinguished in the structure of a steroid?
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What is the correct nomenclature for a double bond between the 5th and 6th carbon atoms in a steroid?
What is the correct nomenclature for a double bond between the 5th and 6th carbon atoms in a steroid?
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How is a side-chain position above the hormone plane indicated in steroid nomenclature?
How is a side-chain position above the hormone plane indicated in steroid nomenclature?
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Study Notes
Steroids
- Cholesterol is a well-known steroid due to its connection to atherosclerosis and heart disease.
- Biochemically, cholesterol is significant as it is the precursor to various important steroids, including:
- Bile acids
- Adrenocortical hormones
- Sex hormones
- Vitamin D
- Steroids are characterized by their cyclopentanoperhydrophenanthrine structure, which features:
- Four rings with 17-carbon atoms
- Additional carbon atoms at positions 13 (C18), 10 (C19), and 17 (C20, 21,...)
- The orientation of the side-chain in a steroid determines its classification as:
- β cis (above the hormone plane)
- α trans (below the hormone plane)
- Double bonds in steroids are represented by Δ (Delta) with the preceding carbon atom number (e.g., Δ5 indicates a double bond between C5 and C6).
- When drawing the structure of a steroid:
- Carbon positions on the steroid nucleus are numbered
- Double bonds are shown as such
- Methyl side chains are depicted as single bonds unattached at the farther (methyl) end
- β-bonds are represented by solid lines, while α-bonds are indicated by broken lines
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