Tetrapyrroles are a class of chemical compounds that contain four

pyrrole Pyrrole is a heterocyclic aromatic organic compound, a five-membered ring with the formula C4 H4 NH. It is a colorless volatile liquid that darkens readily upon exposure to air. Substituted derivatives are also called pyrroles, e.g., ''N''-meth ...

or pyrrole-like rings. The pyrrole/pyrrole derivatives are linked by ( =- or -- units), in either a linear or a cyclic fashion. Pyrroles are a five-atom ring with four carbon atoms and one nitrogen atom. Tetrapyrroles are common cofactors in biochemistry and their biosynthesis and degradation feature prominently in the chemistry of life. Some tetrapyrroles form the active core of compounds with crucial

biochemical Biochemistry or biological chemistry is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology an ...

roles in living systems, such as hemoglobin and

chlorophyll Chlorophyll (also chlorophyl) is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words , ("pale green") and , ("leaf"). Chlorophyll allow plants to a ...

. In these two molecules, in particular, the pyrrole macrocycle ring frames a metal atom, that forms a

coordination compound A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as ''ligands'' or complexing agents. Many ...

with the pyrroles and plays a central role in the biochemical function of those molecules.

Structure

Linear tetrapyrroles (called bilanes) include:Nomenclature of Tetrapyrroles, Appendix 1. Trivially named porphyrins, chlorins, chlorophylls and bilins, fundamental parents
/ref> *Heme breakdown products (e.g.,

bilirubin Bilirubin (BR) (Latin for "red bile") is a red-orange compound that occurs in the normal catabolic pathway that breaks down heme in vertebrates. This catabolism is a necessary process in the body's clearance of waste products that arise from the ...

, biliverdin) *

Phycobilin Phycobilins (from Greek: '' (phykos)'' meaning "alga", and from Latin: ''bilis'' meaning "bile") are light-capturing bilins found in cyanobacteria and in the chloroplasts of red algae, glaucophytes and some cryptomonads (though not in green algae ...

s (found in

cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blu ...

) * Luciferins as found in dinoflagellates and euphausiid shrimps (krill) File:Bilirubin ZZ.png,

Bilirubin Bilirubin (BR) (Latin for "red bile") is a red-orange compound that occurs in the normal catabolic pathway that breaks down heme in vertebrates. This catabolism is a necessary process in the body's clearance of waste products that arise from the ...

File:Biliverdin3.svg, Biliverdin File:Phycoerythrobilin.svg,

Phycoerythrobilin Phycoerythrobilin is a red phycobilin, i.e. an open tetrapyrrole chromophore found in cyanobacteria and in the chloroplasts of red algae, glaucophytes and some cryptomonads. Phycoerythrobilin is present in the phycobiliprotein phycoerythrin, of whi ...

File:Luciferin dinoflagellate.svg,

Dinoflagellate The dinoflagellates (Greek δῖνος ''dinos'' "whirling" and Latin ''flagellum'' "whip, scourge") are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered algae. Dinoflagellates are ...

(R=H) and krill (R=OH) luciferin File:Uroporphyrinogen III skeletal.svg, uroporphyrinogen III, an authentic tetrapyrrole Cyclic tetrapyrroles having four one-carbon bridges include: * Porphin, the simplest tetrapyrrole * Porphyrins, including heme, the core of hemoglobin * Chlorins, including those at the core of chlorophyll. Cyclic tetrapyrroles having three one-carbon bridges and one direct bond between the pyrroles include: * Corrins, including the cores of cobalamins, when complexed with a cobalt ion. File:Heme.svg, Heme group of hemoglobin with a porphin macrocycle. File:C-3 position Chlorophyll a.svg, The chlorin section of the chlorophyll a molecule. The green box shows a group that varies between

types. File:Cobalamin.svg, Cobalamin structure includes a corrin macrocycle. The tetrapyrrole portions of the molecules typically act as

chromophore A chromophore is the part of a molecule responsible for its color. The color that is seen by our eyes is the one not absorbed by the reflecting object within a certain wavelength spectrum of visible light. The chromophore is a region in the molec ...

s because of a high degree of

conjugation Conjugation or conjugate may refer to: Linguistics *Grammatical conjugation, the modification of a verb from its basic form * Emotive conjugation or Russell's conjugation, the use of loaded language Mathematics *Complex conjugation, the change ...

in them. Therefore, these compounds are commonly colored.

References

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