chlorophyll

Chlorophyll is a green pigment essential for photosynthesis in plants, algae, and cyanobacteria. The most common forms in higher plants are chlorophyll a and chlorophyll b; other chlorophylls (c, d, and e) occur in various algae and bacteria. Chlorophylls absorb blue and red light while reflecting green, which gives vegetation its characteristic color. In plants, chlorophyll is located mainly in the chloroplasts, where it participates in light-harvesting complexes that transfer energy to reaction centers.

Chemically, chlorophylls are magnesium-containing porphyrin molecules with a long hydrophobic phytol tail that anchors them in the thylakoid membranes of chloroplasts. The central magnesium ion is coordinated by the porphyrin ring, and structural differences between chlorophyll a and chlorophyll b influence their light-absorption properties. Typical absorption maxima are around 430 nm and 662 nm for chlorophyll a, and around 453 nm and 642 nm for chlorophyll b.

Functionally, chlorophylls act as primary light absorbers in photosystems II and I. They capture photons and transfer excitation energy to reaction centers, where photochemical reactions drive electron transport. This energy conversion yields ATP and NADPH, which fuel the Calvin cycle for carbon fixation and sugar production.

Biosynthesis and ecology: Chlorophyll synthesis occurs in plastids via a conserved tetrapyrrole pathway, with insertion of Mg2+ as a key step. Light conditions regulate both synthesis and degradation; chlorophyll content often declines in autumn as plants reallocate resources.

Significance: Chlorophyll is foundational to most terrestrial photosynthesis, supporting life by converting light energy into chemical energy used for growth and metabolism. It is also used in research and, in derivative forms, as food coloring.