Biomedical Engineering Reference
In-Depth Information
these molecules may have a large number of variations depending on the
cis or trans confi gurations possible (two variations for each double bond),
the different possibilities of amplitude of the angles formed between the
C atoms in the chain and type of functional groups added at the ends of
the molecule. The set of all these factors determines that the carotenoid
molecules have a given size and shape, which are extremely important for
many of the roles played by these compounds.
Although the rules for the carotenoids nomenclature (systematic
names) were published by IUPAC (International Union of Pure and Applied
Chemistry) in 1975, some carotenoids have common names. The specifi c
name is composed of the term carotene preceded by the Greek letters that
refer to the 6 types of end groups that may have the carotenoid in question:
β (beta), γ (gamma), ε (epsilon), κ (kappa), φ (phi), χ (chi) and ψ (psi). The
designation by suffi xes and prefi xes of the other substituent groups, as
well as the numbering system of the different carbon atoms, are also clearly
identifi ed by the IUPAC.
Carotenoid Functions
The usefulness of carotenoids in nature is very diverse. In oxidative
photosynthetic organisms carotenoids are essential compounds with
different functions, the protection against photo-oxidation being the most
important. When in the cytochromes and chlorophyll some molecules
are excited by the effect of light this generates an excited state of these
molecules that have a relatively long life and can cause damage by reacting
with other molecules (such as proteins, lipids, or nucleic acids) or with
oxygen, causing oxidation of the substrate and resulting in the direct
damage of the cellular components. Carotenoids act on these compounds
in the excited state, as well as on oxygen free radicals generated by cellular
metabolism, inactivating them and protecting the cell against these
oxidative agents (Malik 1990, Foote et al. 1991). In these photosynthetic
organisms carotenoids also act as photosynthetic accessory pigments in
photosynthesis, as part of the antenna complexes together with chlorophyll
and usually bind to membrane proteins. In the antenna complexes they
absorb light at different wavelengths from chlorophyll and transmit that
energy with high effi ciency to the action centre, thereby broadening the
solar light absorption spectrum of these organisms (Siefermann-Harms
1985).
The vivid colour of carotenoids is used by many species of plants to
make striking fl owers or fruit, thus attracting animals and thus facilitating
pollination and seed dispersal. The carotenoids colourfulness is also used
by some animals such as insects, crustaceans, fi sh and birds to enhance the
