# DBT JRF 2020 — Question 124

Exam: DBT JRF 2020 · Section: B · Topic: Plant Biology · Difficulty: Hard

## Question

Which one of the following statements is true regarding the magnesium porphyrin ring and the phytol chain of a chlorophyll molecule?

## Options

- **A.** both magnesium porphyrin ring and phytol chain are hydrophilic
- **B.** both magnesium porphyrin ring and phytol chain are lipophilic
- **C.** magnesium porphyrin ring is lipophilic whereas phytol chain is hydrophilic
- **D.** magnesium porphyrin ring is hydrophilic whereas phytol chain is lipophilic

## Answer

Option D

## Explanation

Chlorophyll molecule structure and amphiphilicity: The magnesium-porphyrin (chlorin ring) head group: the tetrapyrrole macrocycle with Mg $^{2+}$ at the centre; has conjugated double bonds enabling light absorption; the ring system is polar/hydrophilic due to polar carbonyl, ester, and ring nitrogen groups — interacts with protein amino acid residues in the photosystem. The phytol chain tail: a long ( $\text{C}_{20}$ ) isoprenoid alcohol ( $E$ -phytol), highly saturated, linear hydrophobic chain — provides the lipophilic anchor that inserts chlorophyll into the non-polar hydrophobic core of the thylakoid membrane phospholipid bilayer. This amphiphilic structure (polar head + hydrophobic tail) is essential for chlorophyll's correct orientation in photosystems I and II.

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