Conchiolins (sometimes referred to as conchins) are complex
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respon ...
s which are secreted by a
mollusc's outer
epithelium (the
mantle).
These proteins are part of a matrix of organic macromolecules, mainly proteins and polysaccharides, that assembled together form the microenvironment where crystals nucleate and grow. This organic matrix also holds and binds to the crystals of
aragonite
Aragonite is a carbonate mineral, one of the three most common naturally occurring crystal forms of calcium carbonate, (the other forms being the minerals calcite and vaterite). It is formed by biological and physical processes, including pre ...
which give such shells their stiffness.
The
ion
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...
s necessary to form
calcium carbonate are also secreted by the mantle, but it is the tailored environment created by the organic matrix which causes aragonite (rather than
calcite
Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on the Mohs scale of mineral hardness, based on scra ...
) crystals to nucleate, in much the same way that
collagen nucleates
hydroxyapatite
Hydroxyapatite, also called hydroxylapatite (HA), is a naturally occurring mineral form of calcium apatite with the formula Ca5(PO4)3(OH), but it is usually written Ca10(PO4)6(OH)2 to denote that the crystal unit cell comprises two entities ...
crystals.
Conchiolin serves as a relatively flexible, crack-deflecting
matrix
Matrix most commonly refers to:
* ''The Matrix'' (franchise), an American media franchise
** '' The Matrix'', a 1999 science-fiction action film
** "The Matrix", a fictional setting, a virtual reality environment, within ''The Matrix'' (franchi ...
for the mineral
aggregate
Aggregate or aggregates may refer to:
Computing and mathematics
* collection of objects that are bound together by a root entity, otherwise known as an aggregate root. The aggregate root guarantees the consistency of changes being made within the ...
particles; its strength and the strong bonding of perlucin can in some cases (such as in the formation of
nacre) give the finished material an impressive level of
toughness
In materials science and metallurgy, toughness is the ability of a material to absorb energy and plastically deform without fracturing.[periostracum
The periostracum ( ) is a thin, organic coating (or "skin") that is the outermost layer of the shell of many shelled animals, including molluscs and brachiopods. Among molluscs, it is primarily seen in snails and clams, i.e. in gastropods a ...]
which is composed of the protein conchiolin. Some land snails (especially the taxa that have become adapted to living on acidic soils) have very thin, transparent, tan-colored shells, even as adults, and those shells are composed entirely of conchiolin.
See also
*
Chitin
Chitin ( C8 H13 O5 N)n ( ) is a long-chain polymer of ''N''-acetylglucosamine, an amide derivative of glucose. Chitin is probably the second most abundant polysaccharide in nature (behind only cellulose); an estimated 1 billion tons of chit ...
*
Corneous
Corneous is a biological and medical term meaning horny, in other words made out of a substance similar to that of horns and hooves in some mammals.
The word is generally used to describe natural or pathological anatomical structures made o ...
*
Mollusc shell
The mollusc (or molluskOften spelled mollusk shell in the USA; the spelling "mollusc" are preferred by ) shell is typically a calcareous exoskeleton which encloses, supports and protects the soft parts of an animal in the phylum Mollusca, which ...
*
Periostracum
The periostracum ( ) is a thin, organic coating (or "skin") that is the outermost layer of the shell of many shelled animals, including molluscs and brachiopods. Among molluscs, it is primarily seen in snails and clams, i.e. in gastropods a ...
*
Sporopollenin
270px, SEM image of pollen grains
Sporopollenin is one of the most chemically inert biological polymers. It is a major component of the tough outer (exine) walls of plant spores and pollen grains. It is chemically very stable and is usually well ...
*
Tectin
External links
''Structure of the conchiolin cases of the prisms in ''Mytilus edulis Charles Grégoire, 1960
Molluscan proteins