Chlorophyll structure: Which long-chain alcohol is esterified to plant chlorophyll molecules as the hydrophobic tail?
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ADolichol
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BFarnesol
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CPhytol
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DRetinol
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ESqualene
Answer
Correct Answer: Phytol
Explanation
Introduction / Context:Chlorophylls are tetrapyrrole pigments with a porphyrin-like ring (chlorin) chelating Mg2+ and a long hydrophobic tail that anchors the molecule in thylakoid membranes. Identifying that tail is fundamental biochemistry.
Given Data / Assumptions:
- Plant chlorophylls a and b share a common hydrophobic tail.
- The tail is an esterified, long-chain isoprenoid alcohol.
- The name of this alcohol is asked.
Concept / Approach:The hydrophobic tail is phytol, a C20 diterpenoid alcohol. It anchors chlorophyll in lipid bilayers and helps orient the light-harvesting complex within photosystems.
Step-by-Step Solution:
Recall chlorophyll anatomy: ring + Mg2+ + phytol tail.Match to options: phytol fits as the canonical tail alcohol.Eliminate other isoprenoids (dolichol, farnesol) that serve different roles.Verification / Alternative check:Structural depictions of chlorophyll a/b consistently label the esterified phytol chain at the ring’s propionic acid side chain.
Why Other Options Are Wrong:
Dolichol: involved in glycoprotein synthesis (dolichol phosphate).Farnesol: precursor in isoprenoid biosynthesis; not the chlorophyll tail.Retinol: vitamin A alcohol; unrelated.Squalene: triterpene hydrocarbon; not an alcohol tail of chlorophyll.Common Pitfalls:Confusing general isoprenoids with the specific phytol tail of chlorophyll.
Final Answer:Phytol.