تمعدن حيوي

Calcitic skeletal parts of belemnites (Jurassic of Wyoming)

التمعدن الحيوي Biomineralization هي إحدى طُرق التمعدن في علم الأحياء، وهي العملية التي تنتج فيها العضويات الحية المعادن [1] غالباً يكون هدفها تقسية وتصليب نسج موجودة. مثل هذه الأنسجة تسمّى بالنسج المتمعدنة وتعد ظاهرة واسعة الانتشار إلى حد كبير، تتضمن جميع الممالك التصنيفية أعداداً قادرة على تشكيل المعادن، وقد حُدد أكثر من 60 معدن مختلف في العضويات.[2][3][4]

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الأحياء

If present on a super-cellular scale, biominerals are usually deposited by a dedicated organ, which is often defined very early in the embryological development. This organ will contain an organic matrix that facilitates and directs the deposition of crystals.[5] The matrix may be collagen, as in deuterostomes,[5] or based on chitin or other polysaccharides, as in molluscs.[6]


تشكل القواقع للمحاريات

Variety of mollusc shells (gastropods, snails and seashells).

The mollusc shell is a biogenic composite material that has been the subject of much interest in materials science because of its unusual properties and its model character for biomineralization. Molluscan shells consist of 95–99% calcium carbonate by weight, while an organic component makes up the remaining 1–5%. The resulting composite has a fracture toughness ~3000 times greater than that of the crystals themselves.[7] In the biomineralization of the mollusc shell, specialized proteins are responsible for directing crystal nucleation, phase, morphology, and growths dynamics and ultimately give the shell its remarkable mechanical strength. The application of biomimetic principles elucidated from mollusc shell assembly and structure may help in fabricating new composite materials with enhanced optical, electronic, or structural properties.

تمعدن العظام

تمعدن العظام هي عملية حيوية ترتبط بها معادن مثل الكالسيوم، الفوسفات، ومعادن أخرى لجعل العظام صلبة. حتى نهاية التسعينيات، اعتقد العلماء أن الاوستيوكالسين، پروتين تصنعه وتفرزه الخلايا العظمية، ويرتبط به الكالسيوم. وفي دراسة أُجريت بمختبر جامعة كلومبيا بنيويورك، عام 2019، على فئران مهندسة وراثياً لا تحتوي على الاوستيوكالسين، كان من المتوقع أن تصبح عظام هذه الفئران هشة، لكن لمن يحدث هذا، فقط حدثت عملية تمعدن العظام بشكل طبيعي تماماً، دون أن يكون للاوستيوكالسين أي تأثير على هذه العملية. وفي الواقع، كانت عظام تلك الفئران أكثر كثافة عن ذي قبل. وعند فحص العظام، تطلب الأمر من الباحثين حفر المزيد من الأنسجة الدهنية، مما يقترح أن غياب الاوستيوكالسين قد أدى إلى تراكم الدهون في أنسجة الفئران.[8] وكان تفسير العلماء أن عند نزع الاوستيوكالسين من العظام انتقل إلى الدم، ومن ثم إلى الأنسجة الدهنية، حيث أثر بطريقة ما على نظام التمثيل الغذائي للفئران، ولعب دوراً في تراكم الدهونأي أن الاوستيوكالسين ليس مجرد پروتين، بل قد يكون هرمون له دور في عملية التمثيل الغذائي. مما يعني العظام مسئولة عن إفراز هرمونات ضرورية لصحة الحيوان، وبهذه النتيجة انضم الهيكل العظمي إلى مجموعة الأنسجة المشاركة مع الغدد الصماء، بالترادف مع الجهاز العصبي لإفراز الهرمونات المنظمة للعمليات الحيوية في الجسم.

انتاج وتحلل المعادن في الفطريات

الكيمياء

Because extracellular[9] iron is strongly involved in inducing calcification,[10][11] its control is essential in developing shells; the protein ferritin plays an important role in controlling the distribution of iron.[12] The most common mineral present in biomineralization is hydroxyapatite (HA), which is a naturally occurring mineral form of calcium apatite with the formula Ca10(PO4)6(OH)2. Hydroxyapatite crystals are found in many biological materials including bones,[13] fish scales,[14] and cartilage.[15] Each material has a mineral content which corresponds with the required mechanical properties, where increasing HA content typically leads to increased stiffness but reduced extensibility.[16]


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التطور

Some calcareous sponges (Ernst Haeckel, Kunstformen der Natur).

The first evidence of biomineralization dates to some 750 مليون سنة مضت,[17][18] and sponge-grade organisms may have formed calcite skeletons 630 مليون سنة مضت.[19] But in most lineages, biomineralization first occurred in the Cambrian or Ordovician periods.[20] Organisms used whichever form of calcium carbonate was more stable in the water column at the point in time when they became biomineralized,[21] and stuck with that form for the remainder of their biological history[22] (but see [23] for a more detailed analysis). The stability is dependent on the Ca/Mg ratio of seawater, which is thought to be controlled primarily by the rate of sea floor spreading, although atmospheric CO2 levels may also play a role.[21]

Glomerula piloseta (Sabellidae), longitudinal section of the tube, aragonitic spherulitic prismatic structure
Type of mineralization Examples of organisms
Calcium carbonate (calcite or aragonite)
Silica
Apatite (phosphate carbonate)

علم الأحياء الفلكي

It has been suggested that biominerals could be important indicators of extraterrestrial life and thus could play an important role in the search for past or present life on Mars. Furthermore, organic components (biosignatures) that are often associated with biominerals are believed to play crucial roles in both pre-biotic and biotic reactions.[24]

On January 24, 2014, NASA reported that current studies by the Curiosity and Opportunity rovers on the planet Mars will now be searching for evidence of ancient life, including a biosphere based on autotrophic, chemotrophic and/or chemolithoautotrophic microorganisms, as well as ancient water, including fluvio-lacustrine environments (plains related to ancient rivers or lakes) that may have been habitable.[25][26][27][28] The search for evidence of habitability, taphonomy (related to fossils), and organic carbon on the planet Mars is now a primary NASA objective.[25][26]

قائمة المعادن

Examples of biogenic minerals include:[29]


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الاستخدامات المحتملة

Most traditional approaches to synthesis of nanoscale materials are energy inefficient, requiring stringent conditions (e.g., high temperature, pressure or pH) and often produce toxic byproducts. Furthermore, the quantities produced are small, and the resultant material is usually irreproducible because of the difficulties in controlling agglomeration.[30] In contrast, materials produced by organisms have properties that usually surpass those of analogous synthetically manufactured materials with similar phase composition. Biological materials are assembled in aqueous environments under mild conditions by using macromolecules. Organic macromolecules collect and transport raw materials and assemble these substrates and into short- and long-range ordered composites with consistency and uniformity. The aim of biomimetics is to mimic the natural way of producing minerals such as apatites. Many man-made crystals require elevated temperatures and strong chemical solutions, whereas the organisms have long been able to lay down elaborate mineral structures at ambient temperatures. Often, the mineral phases are not pure but are made as composites that entail an organic part, often protein, which takes part in and controls the biomineralisation. These composites are often not only as hard as the pure mineral but also tougher, as the micro-environment controls biomineralisation.

ملوثات اليورانيوم في المياه الجوفية

Autunite crystal.

Biomineralization may be used to remediate groundwater contaminated with uranium.[31] The biomineralization of uranium primarily involves the precipitation of uranium phosphate minerals associated with the release of phosphate by microorganisms. Negatively charged ligands at the surface of the cells attract the positively charged uranyl ion (UO22+). If the concentrations of phosphate and UO22+ are sufficiently high, minerals such as autunite (Ca(UO2)2(PO4)2•10-12H2O) or polycrystalline HUO2PO4 may form thus reducing the mobility of UO22+. Compared to the direct addition of inorganic phosphate to contaminated groundwater, biomineralization has the advantage that the ligands produced by microbes will target uranium compounds more specifically rather than react actively with all aqueous metals. Stimulating bacterial phosphatase activity to liberate phosphate under controlled conditions limits the rate of bacterial hydrolysis of organophosphate and the release of phosphate to the system, thus avoiding clogging of the injection location with metal phosphate minerals.[31] The high concentration of ligands near the cell surface also provides nucleation foci for precipitation, which leads to higher efficiency than chemical precipitation.[32]

انظر أيضاً

مصادر

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