Silica Structure Self-assembles

Biological Strategy

AskNature Team

Chemically Assemble Mineral Crystals

The vast majority of biochemical assembly and break down processes––even by the most complex organisms––occur within cells. In fact, cells are able to perform hundreds, even thousands, of chemical transformations at the same time under life-friendly conditions (ambient temperature and pressure in an aqueous environment). Within cells, organisms utilize organic compounds to facilitate the assembly of mineral crystals. For example, oysters utilize acidic proteins and sulfated polysaccharides to assemble layers of aragonite crystals.

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Physically Assemble Structure

Living systems use physical materials to create structures to serve as protection, insulation, and other purposes. These structures can be internal (within or attached to the system itself), such as cell membranes, shells, and fur. They can also be external (detached), such as nests, burrows, cocoons, or webs. Because physical materials are limited and the energy required to gather and create new structures is costly, living systems must use both conservatively. Therefore, they optimize the structures’ size, weight, and density. For example, weaver birds use two types of vegetation to create their nests: strong, a few stiff fibers and numerous thin fibers. Combined, they make a strong, yet flexible, nest. An example of an internal structure is a bird’s bone. The bone is comprised of a mineral matrix assembled to create strong cross-supports and a tubular outer surface filled with air to minimize weight.

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Chemically Assemble Inorganic Compounds

The vast majority of biochemical assembly and break down processes––even by the most complex organisms––occur within cells. In fact, cells are able to perform hundreds, even thousands, of chemical transformations at the same time under life-friendly conditions (ambient temperature and pressure in an aqueous environment). For example, coral polyps transform dissolved calcium and carbonate ions into crystalized calcium carbonate within the calicoblastic cells.

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Sponges

Phylum Porifera (“pore-bearing”): Sponges

Sponges may seem simple, but there’s more to them than meets the eye. True, they don’t have nerves, muscles, or organs. But they do have unique, specialized cells that help them survive. Collar cells have long tails or flagella that line the inner sponge cavity and funnel water through the body. Sponges are filter feeders, taking in large amounts of water and trapping tiny particles to eat. They also have small spiky spicules made of silica or calcium carbonate that help them keep their structure. There are at least 5,000 known species of sponges living in aquatic systems, with 98% of them in the ocean.

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Cell clusters associated with the surface of the giant basal growing spicule of the glass sponge release silica for controlled circumferential growth.

Monorhaphis chuni sponges have evolved the genes to synthesize giant basal spicule that are nearly 3 meters long. The sponge’s cells absorb minute traces of silicic acid from sea water and use it to produce a monolithic amorphous silica rod by concentric deposition. Sclerocytes (a type of cell) form rings around a nascent spicule and produce a called silicatein to convert silicic acid to amorphous silica. Each ring is only 10 microns wide but repeated cycles result in the macroscopic structure that supports the sponge above the sea floor.

Last Updated October 25, 2016

References

“The giant basal spicule of the hexactinellid sponge Monorhaphis chuni represents the longest natural siliceous structure on Earth [3 m long]. This spicule is composed of concentrically arranged lamellae that are approximately 10 ?μm thick…It is shown that the formation of an outermost lamella begins with the association of cell clusters with the surface of the thickening and/or growing spicule. The cells release silica for controlled formation of a lamella. The pericellular (silica) material fuses to a delimited and textured layer of silica with depressions approximately 20–30? μm in diameter. The newly formed layer initially displays 40? μm wide, well-structured banded ribbons and only attains its plain surface in a final step…the depressions are the nests for the silica-forming cells and that silica formation starts with a direct association of silica-forming cells with the outer surface of the spicule, where they remain and initiate the development of the next lamellae.” (Wang et al. 2011:2047)

“Among the metazoans, the siliceous sponges (Porifera:Demospongiae and Hexactinellida) are the only taxa that build their skeleton (spiculae) of amorphous silica (Morse, 1999; Uriz, 2006; Müller et al., 2007d; Ehrlich et al., 2010b). Their silicification deposition–polycondensation pathway is distinguished from others by their ability to take up and accumulate silicic acid from a very silicon-poor aqueous environment (5 ?μmol?l–1)”. (Wang et al. 2011:2047)

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