Phycobilins are the chromophores of phycobiliproteins (photosynthetic pigments) found in cyanobacteria and in the chloroplasts of red algae, glaucophytes and some cryptomonads (though not in green algae and higher plants). The phycobilins serve to capture light energy, which is then passed on to chlorophylls during photosynthesis. They are unique among the photosynthetic pigments in that they are bonded to certain water-soluble proteins, known as phycobiliproteins. A photosynthetic pigment is a pigment present in chloroplasts or photosynthetic bacteria which provides the energy necessary for photosynthesis. ... Orders The taxonomy of the Cyanobacteria is currently under revision. ... The inside of a chloroplast Chloroplasts are organelles found in plant cells and eukaryotic algae which conduct photosynthesis. ... Red algae Classes Florideophyceae Bangiophyceae Cyanidiophyceae The red algae are a large group of mostly multicellular, marine algae, including many notable seaweeds. ... The glaucophytes are a tiny group of freshwater algae. ... Typical genera Campylomonas Chilomonas Chroomonas Cryptomonas Falcomonas Geminigera Goniomonas Guillardia Hemiselmis Plagioselmis Proteomonas Storeatula Rhodomonas Teleaulax The cryptomonads are a small group of flagellates, most of which have chloroplasts. ... Divisions Chlorophyta Charophyta Streptophytina (Subdivision) The green algae are the large group of algae from which the embryophytes (higher plants) emerged. ... Divisions Land plants (embryophytes) Non-vascular plants (bryophytes) Hepatophyta - liverworts Anthocerophyta - hornworts Bryophyta - mosses Vascular plants (tracheophytes) Lycopodiophyta - clubmosses Equisetophyta - horsetails Pteridophyta - true ferns Psilotophyta - whisk ferns Ophioglossophyta - adderstongues Seed plants (spermatophytes) †Pteridospermatophyta - seed ferns Pinophyta - conifers Cycadophyta - cycads Ginkgophyta - ginkgo Gnetophyta - gnetae Magnoliophyta - flowering plants Adiantum pedatum (a fern... Chlorophyll is a green photosynthetic pigment found in plants, algae, and cyanobacteria. ... Leaf. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ...

The phycobilins are especially efficient at absorbing red, orange, yellow and green light, wavelengths which are not well absorbed by chlorophyll a. Organisms growing in shallow waters tend to contain phycobilins that can capture yellow/red light, while those at greater depth often contain more of the phycobilins that can capture green light, which is more abundant there.

There are several types of phycobilins: phycourobilin, phycoerythrobilin, cryptoviolin and phycocyanobilin. They can be found in different combinations attached to phycobiliproteins to confer specific spectroscopic properties. Chemically, phycobilins consist of an open chain of four pyrroles (tetrapyrrole) and are structurally similar to the bile pigment bilirubin. (Bilirubin's structure is also affected by light, a fact used for the phototherapy of jaundiced newborns.) Phycobilins are also closely related to the light-detecting plant pigment phytochrome: a chain of four pyrroles bonded to a protein. Chlorophylls are composed of four pyrroles as well, but there they are arranged in a ring and contain a metal atom in the center. Pyrrole is a heterocyclic aromatic organic compound. ... Bile (or gall) is a bitter, greenish-yellow alkaline fluid secreted by the liver of most vertebrates. ... Bilirubin is a yellow breakdown product of haem (heme in American English). ... Light therapy or phototherapy consists of exposure to specific ranges of light wavelengths (using lasers or LEDs), or very bright, full-spectrum light, for a prescribed amount of time. ... Jaundice, technically known as icterus, is yellowing of the skin, sclera (the white of the eyes) and mucous membranes caused by increased levels of bilirubin in the system. ... Phytochrome is a photoreceptor, a pigment that plants use to detect light. ...

The phycobilins fluoresce at a particular wavelength, and are therefore often used in research as chemical tags, e.g. by binding phycobiliproteins to antibodies in a technique known as immunofluorescence. Fluorescence induced by exposure to ultraviolet light in vials containing various sized cadmium selenide (CdSe) quantum dots. ... Schematic of antibody binding to an antigen An antibody is a protein used by the immune system to identify and neutralize foreign objects like bacteria and viruses. ... Immunofluorescence is the labeling of antibodies or antigens with fluorescent dyes. ...

The name phycobilin comes from the Greek phyco- for "algae", and bilin referring to bile.