Chlorophylls

Chlorophylls are a family of green pigments responsible for capturing light energy in photosynthesis. They share a common structure: a porphyrin ring coordinated to a central magnesium ion, and a hydrophobic phytol side chain that anchors the molecule in the thylakoid membranes of chloroplasts and photosynthetic bacteria.

Chlorophylls function as primary light absorbers in photosystems I and II, forming the light-harvesting antenna and transferring excitation energy to reaction centers where electron transfer begins. Among the chlorophylls, chlorophyll a is universal in oxygenic photosynthesis and serves as the main photochemical pigment; chlorophyll b is an accessory pigment that expands the range of absorbed light by providing energy to chlorophyll a.

Other chlorophylls (such as c, d, e and f) occur in various algae, cyanobacteria, and bacteria, contributing to light absorption in their specific habitats and ecological niches.

Biosynthesis occurs in plastids and chloroplasts via a tetrapyrrole pathway beginning with 5-aminolevulinic acid; magnesium insertion and other steps produce chlorophyll a and b, with regulation by light and developmental signals.

During senescence and leaf abscission, chlorophylls are degraded through a series of steps yielding pheophytins and pheophorbides, resulting in the loss of green color and the appearance of autumn colors. Chlorophylls are also used in agriculture as indicators of plant stress via chlorophyll fluorescence and as dietary supplements and food coloring (chlorophyllin).