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Halobacterium

Halobacterium

See article : Note: The word "halobacterium" is also the singular form of the word "halobacteria". The genus Halobacterium consists of several species of archaea with an obligate aerobic metabolism which require an environment with a high concentration of salt; many of their proteins will not function in low-salt environments. Their cell walls are also quite different from those of bacteria, as ordinary lipoprotein membranes fail in high salt concentrations. In shape, they may be either rods or cocci, and in colour, either red or purple (some species produce bacteriorhodopsin). They reproduce using binary fission (by constriction), and are motile. Genus Halobacterium:
- Halobacterium cutirubrum
- Halobacterium denitrificans
- Halobacterium distributum
- Halobacterium halobium
- Halobacterium lacusprofundi
- Halobacterium mediterranei
- Halobacterium noricense
- Halobacterium pharaonis
- Halobacterium saccharovorum
- Halobacterium salinarium
- Halobacterium sodomense
- Halobacterium trapanicum
- Halobacterium vallismortis
- Halobacterium volcanii

External links

- [http://www.bacterio.cict.fr/h/halobacterium.html List of Prokaryotic Names with Standing in Nomenclature - Genus Halobacterium]
- [http://sn2000.taxonomy.nl/Taxonomicon/TaxonTree.aspx?id=629 Genus Halobacterium] Category:Archaea Category:Extremophiles Category:Phototrophs

Genus

In biology, a genus (plural genera) is a grouping in the classification of living organisms having one or more related and morphologically similar species. In the common binomial nomenclature, the name of an organism is composed of two parts: its genus (always capitalized) and a species modifier. An example is Homo sapiens, the name for the human species which belongs to the genus Homo. See scientific classification for more details of this system. The type genus of a taxon is usually the first genus to be named and described. Families, and in plants all taxa up to division, are named after the type genus. The genus and these higher taxa are typified by a specimen that shows the characteristics of the genus. The specimen used to describe this species is preserved as the holotype and designated as a generitype in a zoological museum or a herbarium to be available for further study. A generic name in one kingdom is allowed to bear the same name as a genus or other taxon name in another kingdom (though this is discouraged by the International Code of Zoological Nomenclature). For instance, Anura is a genus of plants in the family Asteraceae and the order of frogs; Aotus is the genus of golden peas and night monkeys; Oenanthe is the genus of wheatears and water dropworts, and Prunella is the genus of accentors and self-heal. It is, however, not allowed for two genera within the same kingdom to have the same name. This explains why the platypus genus is Ornithorhynchus — although the name Platypus was chosen by George Shaw in 1799, that name had already been given to the ambrosia beetle by Johann Friedrich Wilhelm Herbst in 1793. Since beetles and platypuses are both member of the kingdom Animalia, the name Platypus could not be used for both. Johann Friedrich Blumenbach published the replacement name Ornithorhynchus in 1800.

Archaea

Phylum Crenarchaeota
Phylum Euryarchaeota
    Halobacteria
    Methanobacteria
    Methanococci
    Methanopyri
    Archaeoglobi
    Thermoplasmata
    Thermococci
Phylum Korarchaeota
Phylum Nanoarchaeota The Archaea (also called Archaebacteria) are a major division of living organisms. Although there is still uncertainty in the exact phylogeny of the groups, Archaea, Eukaryotes and Bacteria are the fundamental classifications in what is called the three-domain system. Archaea are, similarly to bacteria, single-celled organisms lacking nuclei and are therefore classified as prokaryotes—known as Monera in the five kingdom taxonomy. They were originally described in extreme environments, but have since been found in all types of habitats.

History

Archaea were identified in 1977 by Carl Woese and George Fox based on their separation from other prokaryotes on 16S rRNA phylogenetic trees. These two groups were originally named the Archaebacteria and Eubacteria, treated as kingdoms or subkingdoms. Woese argued that they represented fundamentally different branches of living things. He later renamed the groups Archaea and Bacteria to emphasize this, and argued that together with Eukarya they comprise three domains of living things.

Archaea, Bacteria and Eukaryotes

Archaea are similar to other prokaryotes in most aspects of cell structure and metabolism. However, their genetic transcription and translation - the two central processes in molecular biology - do not show the typical bacterial features, but are extremely similar to those of eukaryotes. For instance, archaean translation uses eukaryotic initiation and elongation factors, and their transcription involves TATA-binding proteins and TFIIB as in eukaryotes. Several other characteristics also set the Archaea apart. Unlike most bacteria, they have a single cell membrane that lacks a peptidoglycan wall. Further, both bacteria and eukaryotes have membranes composed mainly of glycerol-ester lipids, whereas archaea have membranes composed of glycerol-ether lipids. These differences may be an adaptation on the part of Archaea to hyperthermophily. Archaeans also have flagella that are notably different in composition and development from the superficially similar flagella of bacteria. flagella

Habitats

Many archaeans are extremophiles. Some live at very high temperatures, often above 100°C, as found in geysers and black smokers. Others are found in very cold habitats or in highly saline, acidic, or alkaline water. However, other archaeans are mesophiles, and have been found in environments like marshland, sewage, and soil. Many methanogenic archaea are found in the digestive tracts of animals such as ruminants, termites, and humans. Archaea are usually harmless to other organisms and none are known to cause disease.

Form

Individual archaeans range from 0.1 to over 15 μm in diameter, and some form aggregates or filaments up to 200 μm in length. They occur in various shapes, such as spherical, rod-shaped, spiral, lobed, or rectangular. They also exhibit a variety of different types of metabolism. Of note, the halobacteria can use light to produce ATP, although no Archaea conduct photosynthesis with an electron transport chain, as occurs in other groups.

Evolution and classification

Archaea are divided into two main groups based on rRNA trees, the Euryarchaeota and Crenarchaeota. Two other groups have been tentatively created for certain environmental samples and the peculiar species Nanoarchaeum equitans, discovered in 2002 by Karl Stetter, but their affinities are uncertain. Woese argued that the bacteria, archaea, and eukaryotes each represent a primary line of descent that diverged early on from an ancestral progenote with poorly developed genetic machinery. This hypothesis is reflected in the name Archaea, from the Greek archae or ancient. Later he treated these groups formally as domains, each comprising several kingdoms. This division has become very popular, although the idea of the progenote itself is not generally supported. Some biologists, however, have argued that the archaebacteria and eukaryotes arose from specialized eubacteria. The relationship between Archaea and Eukarya remains an important problem. Aside from the similarities noted above, many genetic trees group the two together. Some place eukaryotes closer to Eurarchaeota than Crenarchaeota are, although the membrane chemistry suggests otherwise. However, the discovery of archaean-like genes in certain bacteria, such as Thermotoga, makes their relationship difficult to determine. Some have suggested that eukaryotes arose through fusion of an archaean and eubacterium, which became the nucleus and cytoplasm, which accounts for various genetic similarities but runs into difficulties explaining cell structure. Single gene sequencing for systematics has led to whole genome sequencing; currently 24 archaeal genomes have been completed with 22 partially completed [http://www.ncbi.nlm.nih.gov/genomes/lproks.cgi].

External links

- [http://www.microbe.org/microbes/archaea.asp Archaea]
- [http://www.archaea.unsw.edu.au/ ArchaeaWeb - by UNSW - Information about Archaea]
- [http://www.ucmp.berkeley.edu/archaea/archaea.html Introduction to the Archaea, ecology, systematics and morphology]
- [http://www.mediscover.net/Extremophiles.cfm Extremophiles Bioprospecting for antimicrobials, Dr Sarah Maloney] Citat: "...Ground breaking research on extremophiles continues to this day, with the recently discovered 22nd genetically encoded amino acid – pyrrolysine – from the archaeon, Methanosarcina barkeri, (Hao et al., 2002; Srinivasan et al., 2002)...."
- [http://news.bbc.co.uk/1/hi/sci/tech/399972.stm BBC News July 21, 1999: Toughest bug reveals genetic secrets] Citat: "...It [Pyrococcus abyssi] likes conditions that the vast majority of other organisms would find impossible to live in. It thrives best at temperatures of about 103 degrees [Celsius] and under pressures of about 200 atmospheres...."
- [http://www.genoscope.cns.fr/Pab/ Pyrococcus abyssi Home page at Genoscope]

References

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- Category:Extremophiles ko:고세균 ja:古細菌

Aerobic

Aerobic is an adjective that means "requiring air" (where "air" usually means oxygen). The opposite of aerobic is anaerobic. See also:
- Aerobic exercise
- Aerobic glycolysis
- Aerobic metabolism
- Aerobic organism
- Aerobic respiration
- Aerobics

Edible salt

:For sour salt, see calcium citrate or citric acid. citric acid Edible salt is a mineral, one of the few rocks humans eat. There are different forms of it: unrefined salt, refined salt, table salt or iodised salt. It is a crystalline solid, white, pale pink or light grey in colour, obtained from seawater or from rock deposits. Sea salt comes in fine or larger crystals. In nature it includes not only sodium chloride, but also other vital trace minerals. Edible rock salts may be slightly greyish in colour due to this mineral content. Salt is necessary for the survival of all living creatures, including humans. Salt is involved in regulating the water content (fluid balance) of the body. Salt flavor is one of the basic tastes. Salt cravings may be caused by trace mineral deficiencies as well as by a deficiency of sodium chloride itself. Salt is required for life, but overconsumption can increase the risk of health problems, including high blood pressure, in those individuals who are genetically predisposed to hypertension. In food preparation, salt is used as a preservative and as a seasoning.

History of edible salt

In the past, salt was difficult to obtain, but had a great importance in food preservation and as a vital food additive. Therefore, it was a highly valued trade item throughout history. Wars were fought over it, states were formed and destroyed because of it. Roman soldiers were partially paid with salt, and this is still evident in the English language as the word salary derives from the Latin word salarium that means payment in salt (Latin sal), as well as the phrase "worth one's salt". It was also of high value to the Hebrews, Greeks and other peoples of antiquity. During the late Roman Empire and throughout the Middle Ages salt was a precious commodity carried along the salt roads into the heartland of the Germanic tribes. Cities, states and dukedoms along the salt roads exacted heavy duties and taxes for the salt passing through their territories. This practise has caused wars, it even caused the formation of cities such as the city of Munich in 1158 when the then Duke of Bavaria Henry XII, called The Lion, decided that the bishops of Freising no longer needed their salt revenue. The gabelle – a French salt tax – was enacted in 1286 and maintained until 1790. Because of the gabelles, common salt was of such a high value that it caused mass population shifts and exodus, attracted invaders and caused wars. In the second half of the 19th century its price finally became more reasonable. At this time, it became possible to mine salt, which is less expensive than evaporating seawater. However, unrefined rock salt lacks many of the trace elements normally found in table salt, making it a poor substitute as an exclusive salt source. The deleterious health effects of the exclusive use of rock salt are similar to the effects of the total lack of salt in one's diet. In India during the time of the British Empire, the government had a monopoly on salt production. Gandhi saw this as wrong. He decided to defy British salt laws as a means of mobilizing popular support for self-rule in India. To protest at the government's salt tax, Gandhi proposed a 240-mile march from Ahmedabad to the coastal town of Dandi. The salt tax charged the Indian people for a basic human necessity and prevented them making their own salt. Gandhi wrote to the Viceroy, Lord Irwin, explaining his intentions: "My ambition is no less than to convert the British people through nonviolence, and thus make them see the wrong they have done to India". When the marchers reached the sea, they started making salt from the sea-water, thus breaking the law. This gesture led to civil disobedience breaking out in many parts of India. 60,000 people were arrested. Ghandi's resistance on salt continues to serve as the model for other modern non-violent efforts to change policy. Today salt is universally accessible, relatively cheap, and iodized.

Forms of edible salt

Unrefined salt

Main articles: Sea salt and Rock salt Some assert that unrefined sea salt is healthier or more 'natural' than refined salts. There are concerns, however, that raw sea or rock salts may not contain sufficient iodine salts to prevent iodine deficiency diseases like goitre.

Refined salt

Refined salt, that is nowadays most widely used, is mainly sodium chloride. Only about 7% of the refined salt is used as a food additive. The majority is sold for industrial use, from manufacturing pulp and paper to setting dyes in textiles and fabric, to producing soaps and detergents, and has great commercial value. The manufacture and use of salt is one of the oldest chemical industries. Salt is also obtained by evaporation of seawater, usually in shallow basins warmed by sunlight; salt so obtained was formerly called bay salt, and is now often called sea salt or solar salt. Today, most refined salt is prepared from rock salt: mineral deposits high in edible salt. These rock salt deposits were formed by the evaporation of ancient salt lakes. These deposits may be mined conventionally or through the injection of water. Injected water dissolves the salt, and the brine solution can be pumped to the surface where the salt is collected. After the raw salt is obtained, it is refined to purify it and improve its storage and handling characteristics. Purification usually involves recrystallization. In recrystallization, a brine solution is treated with chemicals that precipitate most impurities (largely magnesium and calcium salts). Multiple stages of evaporation are then used to collect pure sodium chloride crystals, which are kiln-dried. Anticaking agents (and potassium iodide, for iodized salt) are generally added at this point. These agents are hygroscopic chemicals which absorb humidity, keeping the salt crystals from sticking together. Some anticaking agents used are tricalcium phosphate, calcium or magnesium carbonates, fatty acid salts (acid salts), magnesium oxide, silicon dioxide, sodium alumino-silicate, and alumino-calcium silicate. Concerns have been raised regarding the possible toxic effects of aluminium in the latter two compounds, however both the European Union and the United States FDA permit their use in regulated quantities. The refined salt is then ready for packing and commercial distribution.

Table salt

FDA Table salt is refined salt, containing nearly pure (95% or greater) sodium chloride. It usually contains substances that make it free flowing (anticaking agents). It is common practice to put a few grains of rice in salt shakers to absorb extra moisture when anticaking agents are not enough. Table salt is also often iodized—a small amount of potassium iodide is added as a dietary supplement. Table salt is mainly employed in cooking and as a table condiment. Iodized table salt has essentially eliminated disorders of iodine deficiency in countries where it is used. Iodine is important to prevent the insufficient production of thyroid hormones (hypothyroidism), which can cause goiter, cretinism in children, and myxedema in adults. Table salt is now used all over the world.

Health effects

Sodium is one of the primary electrolytes in the body. Too much or too little salt in the diet can lead to an electrolyte disturbance, which can cause severe, even fatal neurological problems. Excessive consumption of sodium has also been linked to high blood pressure, although it seems likely that the degree of this effect varies greatly depending on the individual. There is no evidence of a causal link between salt intake and mortality or cardio-vascular events. [http://www.saltsense.co.uk/releases/rel013.htm] Salt substitutes (with a taste similar to regular table salt) are available for individuals who wish to restrict their sodium intake. These substitutes contain mostly potassium chloride, which will increase potassium intake. Because excess potassium intake can cause potentially-fatal hyperkalemia, it is advisable to check with one's physician and pharmacist before using salt substitutes. Various diseases and medications may decrease the body's excretion of potassium, thereby increasing the risk of hyperkalemia. The British Food Standards Agency has recently run a controversial public health campaign called "Salt - Watch it" featuring a character called Sid the Slug. The British Salt manufacturers association has found expert opinion which questions the medical view put forward in this campaign. [http://www.saltsense.co.uk/releases/rel015.htm]

External links

- [http://www.people.virginia.edu/~jtd/iccidd/iodman/iodman5.htm Salt production methods and practices]
- [http://www.hungrymonster.com/Foodfacts/Glossary-Terms.cfm?Start_Loop=1&Types_Food_id_int=0&Food_vch=Salmagundi&page_type=Search&pid=8 HungryMonster.com article on edible salt] ja:食塩 ko:소금

Proteins

. This protein was the first to have its structure solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew in 1958, which led to them receiving a Nobel Prize in Chemistry.]] A protein (in Greek πρωτεϊνη = first thread) is a complex, high-molecular-weight organic compound that consists of amino acids joined by peptide bonds. Proteins are essential to the structure and function of all living cells and viruses. Many proteins are enzymes or subunits of enzymes. Other proteins play structural or mechanical roles, such as those that form the struts and joints of the cytoskeleton, serving as biological scaffolds for the mechanical integrity and tissue signalling functions. Still more functions filled by proteins include immune response and the storage and transport of various ligands. In nutrition, proteins serve as the source of amino acids for organisms that do not synthesize those amino acids natively. Proteins are one of the classes of bio-macromolecules, alongside polysaccharides, lipids, and nucleic acids, that make up the primary constituents of living things. They are among the most actively-studied molecules in biochemistry, and were discovered by Jöns Jakob Berzelius in 1838. Almost all natural proteins are encoded by DNA. DNA is transcribed to yield RNA, which serves as a template for translation by ribosomes.

Properties of Protein

Structure

ribosome Main article: Protein structure Proteins are amino acid chains that fold into unique 3-dimensional structures. The shape into which a protein naturally folds is known as its native state, which is determined by its sequence of amino acids. Thus, proteins are their own polymers, with amino acids being the monomers. Biochemists refer to four distinct aspects of a protein's structure:
- Primary structure: the amino acid sequence
- Secondary structure: highly patterned sub-structures—alpha helix and beta sheet—or segments of chain that assume no stable shape. Secondary structures are locally defined, meaning that there can be many different secondary motifs present in one single protein molecule.
- Tertiary structure: the overall shape of a single protein molecule; the spatial relationship of the secondary structural motifs to one another
- Quaternary structure: the shape or structure that results from the union of more than one protein molecule, usually called subunit proteins subunits in this context, which function as part of the larger assembly or protein complex. In addition to these levels of structure, proteins may shift between several similar structures in performing their biological function. In the context of these functional rearrangements, these tertiary or quaternary structures are usually referred to as "conformations," and transitions between them are called conformational changes. Proteins are separated into two groups: Complete and Incomplete. Incomplete proteins are from plants and do not include all 20 amino acids. Complete proteins come from an animal and include all 20 amino acids. You get protein from mostly everything you eat, but whether all the amino acids are in them depends on what the substance is. The primary structure is held together by covalent peptide bonds, which are made during the process of translation. The secondary structures are held together by hydrogen bonds. The tertiary structure is held together primarily by hydrophobic interactions but hydrogen bonds, ionic interactions, and disulfide bonds are usually involved too. The process by which the higher structures form is called protein folding and is a consequence of the primary structure. The mechanism of protein folding is not entirely understood. Although any unique polypeptide may have more than one stable folded conformation, each conformation has its own biological activity and only one conformation is considered to be the active, or native conformation. The two ends of the amino acid chain are referred to as the carboxy terminus (C-terminus) and the amino terminus (N-terminus) based on the nature of the free group on each extremity.

Working with proteins

Proteins are sensitive to their environment. They may only be active in their native state, over a small pH range, and under solution conditions with a minimum quantity of electrolytes. A protein in its native state is often described as folded. A protein that is not in its native state is said to be denatured. Denatured proteins generally have no well-defined secondary structure. Many proteins denature and will not remain in solution in distilled water. One of the more striking discoveries of the 20th century was that the native and denatured states in many proteins were interconvertible, that by careful control of solution conditions (by for example, dialyzing away a denaturing chemical), a denatured protein could be converted to native form. The issue of how proteins arrive at their native state is an important area of biochemical study, called the study of protein folding. Through genetic engineering, researchers can alter the sequence and hence the structure, "targeting", susceptibility to regulation and other properties of a protein. The genetic sequences of different proteins may be spliced together to create "chimeric" proteins that possess properties of both. This form of tinkering represents one of the chief tools of cell and molecular biologists to change and to probe the workings of cells. Another area of protein research attempts to engineer proteins with entirely new properties or functions, a field known as protein engineering. Protein-protein interactions can be screened for using two-hybrid screening.

Protein regulation

Various molecules and ions are able to bind to specific sites on proteins. These sites are called binding sites. They exhibit chemical specificity. The particle that binds is called a ligand. The strength of ligand-protein binding is a property of the binding site known as affinity. Since proteins are involved in practically every function performed by a cell, the mechanisms for controlling these functions therefore depend on controlling protein activity. Regulation can involve a protein's shape or concentration. Some forms of regulation include:
- Allosteric modulation: When the binding of a ligand at one site on a protein affects the binding of ligand at another site.
- Covalent modulation: When the covalent modification of a protein affects the binding of a ligand or some other aspect of the protein's function.

Diversity

Proteins are generally large molecules, having molecular masses of up to 3,000,000 (the muscle protein titin has a single amino acid chain 27,000 subunits long). Such long chains of amino acids are almost universally referred to as proteins, but shorter strings of amino acids are referred to as "polypeptides," "peptides" or rarely, "oligopeptides". The dividing line is undefined, though "polypeptide" usually refers to an amino acid chain lacking tertiary structure which may be more likely to act as a hormone (like insulin), rather than as an enzyme (which depends on its defined tertiary structure for functionality). Proteins are generally classified as soluble, filamentous or membrane-associated (see integral membrane protein). Nearly all the biological catalysts known as enzymes are soluble proteins (with a recent notable execption being the discovery of ribozymes, RNA molecules with the catalytic properties of enzymes.) Antibodies, the basis of the adaptive immune system, are another example of soluble proteins. Membrane-associated proteins include exchangers and ion channels, which move their substrates from place to place but do not change them; receptors, which do not modify their substrates but may simply shift shape upon binding them. Filamentous proteins make up the cytoskeleton of cells and much of the structure of animals: examples include tubulin, actin, collagen and keratin, all of which are important components of skin, hair, and cartilage. Another special class of proteins consists of motor proteins such as myosin, kinesin, and dynein. These proteins are "molecular motors," generating physical force which can move organelles, cells, and entire muscles. muscle

Role of Protein

Functions

Proteins are involved in practically every function performed by a cell, including regulation of cellular functions such as signal transduction and metabolism. For example, protein catabolism requires enzymes termed proteases and other enzymes such as glycosidases.

Within Nutrition

Protein is an important macronutrient to the human diet, supplying the body's needs for nitrogen and amino acids, the building blocks of proteins. The exact amount of dietary protein needed to satisfy these requirements may vary widely depending on age, sex, level of physical activity, and medical condition, as well as the RDA specified by the state. The recommended intake of protein differs from country to country, but it is marginalised between 0.8 and 1.2g / kg b.w (Per kilogram of bodyweight), however , in more serious athletes, requiring strength, the figure is somewhat between 1.0 and 2.0g per kilogram of Body weight, which is referred to as the maximum protein intake:benefits ratio. Although proteins are found in all foods, be it only in small amounts , protein is still well concentrated in foods such as legumes, nuts, and dairy products, the majority of which are protein choices for vegetarians. Protein is the major component in the regulation, growth and differentation of muscles, tendons, enzymes, skin, hair, eyes, as well as a tremendous variety of other organs and processes. The quality of protein intake is particularly important because different proteins supply essential amino acids in different proportions. Given an adequate intake of nitrogen, the human body can manufacture 10 of the 18 amino acids from glucose. The remaining 8 amino acids (threonine, valine, tryptophan, isoleucine, leucine, lysine, phenylalanine, and methionine) cannot be manufactured by the body and must be acquired through supplementation. Thus, they are termed essential amino acids. For use within the body, the majority of protein taken from food consumed is converted by protein catabolism into ammonia which, due to its toxicity, must be converted to either urea or uric acid,or in some animals is excreted in urine. Proteins possessing equal proportions of all essential amino acids in relatively abundant quantities are often termed "complete", or "High-Quality" Proteins, which are generally obtained from animal proteins, such as meat , and are rated using PDCAAS (Protein Digestibility Corrected Amino Acid Score). Despite what the name suggests, quality proteins are not essential for good supplementation or nutrition within the average person, however, the difference between amino acids in plant and animal proteins is discernable, particularly for athletes or bodybuilders as plant proteins lack two major amino acids found in animal proteins; lysine within grains, and methionine within legumes, major benefactors to a major athlete's dietary regime. Neverthelss, in terms of quality, amino acids found in plant and animal extracts are identical. Protein deficiency can lead to symptoms such as fatigue, insulin resistance, hair loss, loss of hair pigment, loss of muscle mass , low body temperature, hormonal irregularities, as well as loss of skin elsaticity . Severe protein deficiency, encountered only in times of famine, is fatal, due to the lack of material for the body to facilitate as energy. It has been known that in some "wild diets", in which people lose mass amounts of weight in a short period of time are attributed to deficiencies in protein, and thus loss in muscle mass, and not fat, which is widely known as a dangerous practice, particularly because of the benefits of muscle mass over fat. Excessive protein intake has also been linked to several problems;
- overreaction within the immune system
- liver dysfunction due to increased toxic residues
- loss of bone density, frailty of bones due to increased acidity in the blood and foundering (foot problems) in horses. It is assumed by reasearchers on the field, that excessive intake of protein forced increased calcium excretion. If there is to be excessive intake of protein, it is thought that a regular intake of calcium would be able to stablilise, or even increase the uptake of calcium by the small intestine, which would be more beneficial in older women . Proteins are often progenitors in allergies and allergic reactions to certain foods. This is because the structure of each form of protein is slightly different; some may trigger a response from the immune system while others remain perfectly safe. Many people are allergic to casein, the protein in milk; gluten, the protein in wheat and other grains; the particular proteins found in peanuts; or those in shellfish or other seafoods. It is extremely unusual for the same person to adversely react to more than two different types of proteins, due to the diversity between protein or amino acid types.

History

The first mention of the word protein, which means of first rank, were from a letter sent by Jöns Jakob "Jinglehimer Schmidt" Berzelius to Gerhardus Johannes Mulder on 10. July 1838, where he wrote: :«Le nom protéine que je vous propose pour l’oxyde organique de la fibrine et de l’albumine, je voulais le dériver de πρωτειοξ, parce qu’il paraît être la substance primitive ou principale de la nutrition animale.» Translated as: :"The name protein that I propose for the organic oxide of fibrin and albumin, I wanted to derive from [the Greek word] πρωτειοξ, because it appears to be the primitive or principal substance of animal nutrition." Investigation of proteins and their properties had been going on since about 1800 when scientists were finding the first signs of this, at the time, unknown class of organic compounds.

References

# Kerstetter, J. E., O'Brien, K. O., Insogna, K. L. (2003) "[http://www.ajcn.org/cgi/content/full/78/3/584S Dietary protein, calcium metabolism, and skeletal homeostasis revisited]" . J Clin Endocrinol Metab Vol 78, p584S-592S. # Kerstetter, J. E., O'Brien, K. O., Caseria, D.M, Wall, D. E. & Insogna, K. L (2005) "The impact of dietary protein on calcium absorption and kinetic measures of bone turnover in women" . J Clin Endocrinol Metab (2005) Vol 90, p26-31, . # Devine, A., Dick, I. M,, Islam I. M., Dhaliwal, S. S. & Prince, R. L. (2005) "Protein consumption is an important predictor of lower limb bone mass in elderly women" . Am J Clin Nutr (2005) volume 81 pages 423-428, . # Jeukendrup, A. & Gleeson, M. (2004) Sport Nutrition - An Introduction to Energy Production and Performance USA : Human Kinetics # Bean, A. (2004) Sport Nutrition for Serious Athletes London : Routledge

External links

- [http://www.expasy.uniprot.org UniProt the Universal Protein Resource]
- [http://www.proteinatlas.org Human Protein Atlas]
- [http://www.ihop-net.org/UniPub/iHOP/ iHOP - Information Hyperlinked over Proteins]
- [http://www.biochemweb.org/proteins.shtml Proteins: Biogenesis to Degradation - The Virtual Library of Biochemistry and Cell Biology]
- [http://web.mit.edu/lms/www/ MIT's Laboratory for Protein Molecular Self-Assembly]
- [http://www.puramatrix.com/pubs Numerous publications on synthetic biomimetic protein-based biomaterials]
- [http://www.westernblotting.org Protein Research: Western Blot Protocols, Troubleshooting and Theory]
- [http://www.rcsb.org The Protein Databank: The single worldwide repository for the processing and distribution of 3-D biological macromolecular structure data.]
- [http://web.indstate.edu/thcme/mwking/amino-acid-metabolism.html Amino acid metabolism]
- [http://www.biochem.szote.u-szeged.hu/astrojan/protein2.htm Protein Images] Category:Molecular biology Category:Biochemistry Category:Nutrition zh-min-nan:Nn̄g-pe̍h-chit ko:단백질 ja:蛋白質 simple:Protein th:โปรตีน

Bacteria

Actinobacteria
Aquificae
Bacteroidetes/Chlorobi
Chlamydiae/Verrucomicrobia
Chloroflexi
Chrysiogenetes
Cyanobacteria
Deferribacteres
Deinococcus-Thermus
Dictyoglomi
Fibrobacteres/Acidobacteria
Firmicutes
Fusobacteria
Gemmatimonadetes
Nitrospirae
Planctomycetes
Proteobacteria
Spirochaetes
Thermodesulfobacteria
Thermomicrobia
Thermotogae Bacteria (singular: bacterium) are a major group of living organisms. Most are microscopic and unicellular, with a relatively simple cell structure lacking a cell nucleus, and organelles such as mitochondria and chloroplasts. Their cell structure is further described in the article about prokaryotes, because bacteria are prokaryotes, in contrast to organisms with more complex cells, called eukaryotes. The term "bacteria" has variously applied to all prokaryotes or to a major group of them, otherwise called the eubacteria, depending on ideas about their relationships. In Wikipedia, bacteria is used specifically to refer to the eubacteria. Bacteria are the most abundant of all organisms. They are ubiquitous in soil, water, and as symbionts of other organisms. Many pathogens are bacteria. Most are minute, usually only 0.5-5.0 μm in their longest dimension, although giant bacteria like Thiomargarita namibiensis and Epulopiscium fishelsoni may grow past 0.5 mm in size. They generally have cell walls, like plant and fungal cells, but with a very different composition (peptidoglycans). Many move around using flagella, which are different in structure from the flagella of other groups.

History and taxonomy

The first bacteria were observed by Antony van Leeuwenhoek in 1683 using a single-lens microscope of his own design. The name bacterium was introduced much later, by Ehrenberg in 1828, derived from the Greek word βακτηριον meaning "small stick". Louis Pasteur (1822-1895) and Robert Koch (1843-1910) described the role of bacteria as conveyors and causes of disease or pathogens.

Metabolism

Bacteria show a wide variety of different metabolisms and can accordingly be classified into primary nutritional groups. The most common division is between heterotrophs, which depend on an organic source of carbon, and autotrophs, which are able to synthesize organic compounds from carbon dioxide and water. Autotrophs that obtain energy by oxidizing chemical compounds are called chemotrophs, and those that obtain their energy from light, via photosynthesis, are called phototrophs. There are many variations on this terminology such as chemoautotrophs and photosynthetic autotrophs and so on. In addition, bacteria are distinguished based on the source of reducing equivalents they are using. Those using inorganic compounds (e. g. water, hydrogen, sulfide or ammonia) for this purpose are called lithotrophs and others needing organic compounds (e. g. sugars or organic acids) and are called organotrophs. The metabolic modes of energy metabolism (phototrophy or chemotrophy), reducing equivalent sources (lithotrophy or organotrophy) and carbon sources (autotrophy or heterotrophy) can be combined differently in any single microorganism, and even shifting between different modes frequently occurs in many species. Other nutritional requirements include nitrogen, sulfur, phosphorus, vitamins and metallic elements such as sodium, potassium, calcium, magnesium, manganese, iron, zinc, cobalt, copper and nickel for normal growth. For some species, additional trace elements such as selenium, tungsten, vanadium or boron are needed. Based on their response to oxygen, most bacteria can be placed into one of three groups: Some bacteria can grow only in the presence of oxygen and are called aerobes; others can grow only in the absence of oxygen and are called anaerobes; and some can grow in the presence or absence of oxygen and are called facultative anaerobes.

Movement

Motile bacteria can move about, either using flagella, bacterial gliding, or changes of buoyancy. A unique group of bacteria, the spirochaetes, have structures similar to flagella, called axial filaments, between two membranes in the periplasmic space. They have a distinctive helical body that twists about as it moves. Bacterial flagella are arranged in many different ways. Bacteria can have a single polar flagellum at one end of a cell, clusters of many flagella at one end or flagella scattered all over the cell, as with Peritrichous. Many bacteria (such as E.coli) have two distinct modes of movement: forward movement (swimming) and tumbling. The tumbling allows them to reorient and introduces an important element of randomness in their forward movement. (see external links below for link to videos). Motile bacteria are attracted or repelled by certain stimuli, behaviors called taxes - for instance, chemotaxis, phototaxis, mechanotaxis and magnetotaxis. In one peculiar group, the myxobacteria, individual bacteria attract to form swarms and may differentiate to form fruiting bodies. The myxobacteria move only when on solid surfaces, unlike E. coli which is motile in liquid or solid media.

Groups and identification

myxobacteria Bacteria come in a variety of different shapes. Most are rod-shaped, sphere-shaped, or helix-shaped; these are respectively referred to as bacilli, cocci, and spirilla. An additional group, vibrios, are comma-shaped. Shape is no longer considered a defining factor in the classification of bacteria, but many genera are named for their shape (e.g. Bacillus, Streptococcus, Staphylococcus) and it is an important part in their identification. Another important tool is Gram staining, named after Hans Christian Gram who developed the technique. This separates bacteria into two groups, based on the composition of their cell wall. The first formal grouping of bacteria into phyla was based largely on this test:
- Gracilicutes - bacteria with a second cell membrane containing lipids, giving them Gram-negative stains
- Firmicutes - bacteria with a single membrane and thick peptidoglycan wall, giving them Gram-positive stains
- Mollicutes - bacteria with no second membrane or wall, giving them Gram-negative stains The archeabacteria were originally included as the Mendosicutes. As given, these phyla are no longer believed to represent monophyletic groups. The Gracilicutes have been divided into many different phyla. Most gram-positive bacteria are placed in the phyla Firmicutes and Actinobacteria, which are closely related. However, the Firmicutes have been redefined to include the mycoplasmas (Mollicutes) and certain Gram-negative bacteria.

Benefits and dangers

Bacteria are both harmful and useful to the environment, and animals, including humans. The role of bacteria in disease and infection is important. Some bacteria act as pathogens and cause tetanus, typhoid fever, pneumonia, syphilis, cholera, foodborne illness and tuberculosis. Sepsis, a systemic infectious syndrome characterized by shock and massive vasodilation, or localized infection, can be caused by bacteria such as streptococcus, staphylococcus, or many gram-negative bacteria. Some bacterial infections can spread throughout the host's body and become systemic. In plants, bacteria cause leaf spot, fireblight, and wilts. The mode of infection includes contact, air, food, water, and insect-borne microorganisms. The hosts infected with the pathogens may be treated with antibiotics, which can be classified as bacteriocidal and bacteriostatic, which at concentrations that can be reached in bodily fluids either kill bacteria or hamper their growth, respectively. Antiseptic measures may be taken to prevent infection by bacteria, for example, prior to cutting the skin during surgery or swabbing skin with alcohol when piercing the skin with the needle of a syringe. Sterilization of surgical and dental instruments is done to make them sterile or pathogen-free to prevent contamination and infection by bacteria. Sanitizers and disinfectants are used to kill bacteria or other pathogens to prevent contamination and risk of infection. In soil, microorganisms help in the transformation of nitrogen to ammonia with enzymes secreted by these microbes, which reside in the rhizosphere (a zone that includes the root surface and the soil that adheres to the root after gentle shaking). Some bacteria are able to use molecular nitrogen as their source of nitrogen, converting it to nitrogenous compounds, a process known as nitrogen fixation. Many other bacteria are found as symbionts in humans and other organisms. For example, the presence of the gut flora in the large intestine can help prevent the growth of potentially harmful microbes. The ability of bacteria to degrade a variety of organic compounds is remarkable. Highly specialized groups of microorganisms play important roles in the mineralization of specific classes of organic compounds. For example, the decomposition of cellulose, which is one of the most abundant constituents of plant tissues, is mainly brought about by aerobic bacteria that belong to the genus Cytophaga. This ability has also been utilized by humans in industry, waste processing, and bioremediation. Bacteria capable of digesting the hydrocarbons in petroleum are often used to clean up oil spills. Some beaches in Prince William Sound were fertilized in an attempt to facilitate the growth of such bacteria after the infamous 1989 Exxon Valdez oil spill. These efforts were effective on beaches that were not too thickly covered in oil. Bacteria, often in combination with yeasts and molds, are used in the preparation of fermented foods such as cheese, pickles, soy sauce, sauerkraut, vinegar, wine, and yogurt. Using biotechnology techniques, bacteria can be bioengineered for the production of therapeutic drugs, such as insulin, or for the bioremediation of toxic wastes.

Miscellaneous

Two organelles, mitochondria and chloroplasts, are generally believed to have been derived from endosymbiotic bacteria. Microorganisms are widely distributed and are most abundant where they have food, moisture, and the right temperature for their multiplication and growth. They can be carried by air currents from one place to another. The human body is home to billions of microorganisms; they can be found on skin surfaces, in the intestinal tract, in the mouth, nose, and other body openings. They are in the air one breathes, the water one drinks, and the food one eats. The great antiquity of the bacteria has enabled them to evolve a great deal of genetic diversity. They are far more diverse than, say, the mammals or insects. For instance, the genetic distance between E. coli and Thermus aquaticus is greater than the distance between humans and oak trees.

References

- Some text in this entry was merged with the Nupedia article entitled Bacteria, written by Nagina Parmar; reviewed and approved by the Biology group (editor: Gaytha Langlois, lead reviewer: Gaytha Langlois, lead copyeditors: Ruth Ifcher and Jan Hogle)
-

External links

- [http://www.dsmz.de/bactnom/bactname.htm Bacterial Nomenclature Up-To-Date from DSMZ]
- [http://www.sciencenews.org/pages/sn_arc99/4_17_99/fob5.htm The largest bacteria]
- [http://tolweb.org/tree?group=Eubacteria&contgroup=Life_on_Earth Tree of Life]
- [http://www.rowland.harvard.edu/labs/bacteria/index_movies.html Videos] of bacteria swimming and tumbling, use of optical tweezers and other fine videos.
- Category:Bacteriology ko:세균 ja:真正細菌 th:แบคทีเรีย

Membranes

A membrane is a thin, typically planar structure or material that separates two environments. Because it sits between environments or phases and has a finite volume, it can be referred to as an interphase rather than an interface. Membranes selectively control mass transport between the phases or environments. Biological membranes include:
- Cell membrane and intracellular membranes
- mucous membrane
- S-layer Artificial membranes are used in:
- Reverse osmosis
- Filtration (Microfiltration, Ultrafiltration)
- Pervaporation
- Dialysis
- Electrodialysis
- Emulsion liquid membranes
- Membrane-based solvent extraction
- Membrane reactors
- Gas permeation
- supported liquid membranes Theoretical membranes are used in:
- M-theory (simplified) simple:Membranes

Bacteriorhodopsin

Bacteriorhodopsin is the photosynthetic pigment used by archaea, most notably halobacteria. It acts as a proton pump, i.e. it captures light energy and uses it to move protons across the membrane out of the cell. The resulting proton gradient is subsequently converted into chemical energy. Bacteriorhodopsin is an integral membrane protein composed of three identical chains. Each chain has seven transmembrane alpha helices and contains one molecule of retinal buried deep within. It is the retinal molecule that changes its conformation when absorbing a photon, resulting in a conformational change of the surrounding protein and the proton pumping action. The bacteriorhodopsin molecule is purple and is most efficient at absorbing green light (wavelength 500-650 nm, with the absorption maximum at 568 nm). The three-dimensional tertiary structure of bacteriorhodopsin resembles that of vertebrate rhodopsins, the pigments that sense light in the retina. Rhodopsins also contain retinal, however the functions of rhodopsin and bacteriorhodopsin are different and there is no homology of their amino acid sequences. Both rhodopsin and bacteriorhodopsin belong to the 7TM receptor family of proteins, but rhodopsin is a G protein coupled receptor and bacteriorhodopsin is not. In the first use of electron crystallography to obtain an atomic-level protein structure, the structure of bacteriorhodopsin was resolved in 1990. It was then used as a template to build models of other G protein-coupled receptors before crystallographic structures were also available for these proteins. Many molecules have homology to bacteriorhodopsin, including some directly light-activated channels like channelrhodopsin. All other photosynthetic systems in bacteria, algae and plants use chlorophylls or bacteriochlorophylls rather than bacteriorhodopsin. These also produce a proton gradient, but in a quite different and more indirect way involving an electron transfer chain consisting of several other proteins. Furthermore, chlorophylls are aided in capturing light energy by other pigments known as "antennas"; these are not present in bacteriorhodopsin based systems. Lastly, chlorophyll-based photosynthesis is coupled to carbon fixation (the incorporation of carbon dioxide into larger organic molecules); this is not true for bacteriorhodopsin-based system. It is thus likely that photosynthesis independently evolved at least twice, once in bacteria and once in archaea.

External link

- [http://www.rcsb.org/pdb/molecules/pdb27_1.html Bacteriorhodopsin - PDB molecule of the month] Category:7TM receptors Category:Pigments Category:Photosynthesis ja:バクテリオロドプシン

Motile

Motility is the ability to move spontaneously and independently. The term can apply to single cells, or to multicellular organisms. Often, in cellular biology or biomedical engineering, motility refers to directed cell movement down gradients established in biopolymers. Example are:
- movement along a chemical gradient (see chemotaxis)
- movement along a rigidity gradient (see durotaxis)
- movement along a gradient of cell adhesion sites (see haptotaxis) More information on cell motility can be found under cell biology. Motility is also a term referring to the movement of stool through the intestines. How do cells move? All living things need some basic raw materials and energy for survival, and as the world is not generally kind enough to deliver these things right to the organism, many have evolved ways of bringing themselves to where they want to be. In this essay I will look into how individual cells propel themselves around the world, or even just get part of themselves there, which is often good enough. The first method of movement I would like to discuss is the ability of some cells to crawl over their substrate by sending out extensions of their plasmalemma and cytoplasm called filopodia, anchoring themselves by said extension, then dragging themselves towards the anchor, or flowing into the filopodium. This mechanism of movement is famously used by amoeboid organisms, but is also used by lymphocytes, neutrophils and keratocytes to reach the sites of injury or infection to which they respond, and by cells in developing embryos to get where they ought to be, and to shape their substrate with their passage. To understand this mechanism of movement we must first examine the nature of the actin: Actin is a protein monomer that can assemble into filaments by attaching in a twisting manner so that each molecule of actin in a filament (bar the ones on the end) is bonded non-covalently with 4 other actin molecules; resulting in helictical fibres. This makes actin filaments much more stable then if the monomers only bonded with two other monomers. The advantage of actin filaments being composed of multiple monomers is that it allows the components of actin filaments (which may have to stretch the width of a cell) to diffuse around the cell and be available where required. Large structures can be assembled where required, then disassembled when no longer needed and diffused until they are again needed somewhere else. However, actin is also liable to disassociate from the filament, so dimers are relatively unstable. However, a trimer of actin is much more stable, as there are more contacts between adjacent monomers. Thus, in vitro, actin in solution displays a lag time before it starts assembling into microfilaments, as it takes a while for the chance occurrence of enough additions to form a nucleus. Addition of pre-made nuclei removes this lag phase. The number of monomers that add to the actin filament (or microtubule, for that matter) is proportional to the concentration of free subunits in the solution. However, subunits will leave the polymer at a constant rate independent of the rate of addition. Thus, as free subunits are used up from the surrounding to make polymers, the rate of addition will drop until it reaches the critical concentration: the concentration at which addition and loss are equal. The polymer is not stable: it is constantly losing subunits (usually from one end, called the minus end, which due to the structure of actin has a lower affinity for other actin monomers) and gaining units (from the plus end, which has a higher affinity for actin monomers); this effect is known as treadmilling. Cells can control the formation of microfilaments by making nuclei available to skip the lag phase. These nuclei take the form of actin related proteins (ARPs), which are 45% similar to actin; ARP complexes composed of ARP2 and ARP3 and other proteins act as nuclei for the minus end of actin filaments, stabilising the minus end thus promoting elongation at the plus end. However, this only promotes filament growth: if this were the only control mechanism other random filaments would occur in the cell as in solution actin in vitro the critical concentration of actin is 1 μM, and the rest would turn eventually into microfilaments. In the cytosol actin is divided about 50/50 between free monomers and filaments. This reduction in how much actin is polymerised is achieved by special proteins, the most common of which is thymosin. Thymosin binds to actin monomers preventing them from binding to other actin monomers. Thus normally actin is prevented from forming polymers. Another protein, profilin, competes with thymosin, and when profilin binds to an actin monomer the resultant actin-profilin complex can attach to the plus end of microfilament (or filament nucleus), but not the minus end. The binding of the actin-profilin complex causes a conformational change in the actin, reducing its affinity for profilin, and the profilin disassociates. Now we can start to see how this is used as a means of movement: profilin is localised on the cytosolic face of the plasmalemma because it binds to acidic phospholipids that are found there. Thus the actin pushes out, forming extensions in the membrane – our filopodia or lemellipodia, by a process called protrusion. Protrusion can come in the form of filopodia (a spike of actin pushing out making a long, thing and narrow protrusion), lamellipodia (sheet like structures that are long, thing and wide) and pseudopodia (stubby three dimensional protrusions filled with actin gel). Now all we need is an anchor and a mechanism for pulling on the anchor. The anchor comes in the form of Focal Contacts. Focal Contacts are points produced on the newly protruded protrusion containing integrins where the plasma membrane is very close to the substrate. The actin filaments are connected to the intergrins that connect to the substrate, and attachment is achieved. Now the actin filaments, which are usually attached to each other by ARP complexes forming a web, which undergoes treadmilling: assembling at the front and disassembling at the back. Cofilin is used to control unidirectional movement as it will bind preferentially and cause depolymerisation to actin that contains ADP, thus the later parts of the web are targeted over the newly polymerised parts. Actin acts as an enzyme, and while ATP hydrolysis rates are very low in the monomer form, in the polymer form hydrolysis of ATP to ADP is much higher. Thus traction is achieved by treadmilling. The mechanism by which the contents of the cell move forward is not fully understood, but it is known that these forces are generated by myosin II. Contraction of the actin cortex at the posterior end helps weaken older focal points. And thus, the cell crawls forward. The next method of cell motility I would like to discuss is the eukaryotic flagella and cilia. These, like filopodia, are extensions of the cytoplasm, but in this case they are caused by the protrusion of tubulin. Tubulin is a protein that can assemble into microtubules by the polymerisation of many tubulin dimers. Tubulin dimers are composed of two separate proteins: α-tubulin and β-tubulin. These dimers assemble head to tail to form protofilaments. 12 protofilaments line up side by side and curve around to form a hollow tube – this is a microtubule. Cilia and flagella have a core (called an axoneme) of 9 outer doublet microtubules, which consist of a full microtubule and a partial microtubule fused together, with a pair of full microtubules in the centre. The outer doublet microtubules are connected to the inner singlet tubules by radial spokes, and are connected to their neighbouring doublet tubules by nexin. The doublet microtubules are also attached to each other by dynein. This molecule has a motor domain that when activated by ATP hydrolysis ‘walks’ along the adjacent doublet microtubule by a mechanism similar to myosin in muscle cells. This would make the microtubules slide past each other if it was not for the connective nexin. As they are connected by nexin, a bending motion occurs, thus making the cilia or flagella wave back and forth. This can propel the cell forward in a liquid medium: either one or a few large flagella are used (as in sperm cells) or banks of shorter cilia beating slightly out of synchrony to produce a waving effect. Eukaryotic flagella however are totally different to prokaryotic flagella; a prokaryotic flagellum is a helically shaped filament of the protein flagellin attached to a base called a Hook, as it is bent at a significant angle. This hook is spun clockwise or anticlockwise by Mot complexes – the direction being controlled by Fli proteins. The Mot complexes are powered by an H+ gradient set up by actively pumping H+ out of the cytoplasm. The collective term for the Mot protein, Fli protein and various anchorage rings complex is the basal body. Flagella are arranged differently on different bacteria – either at one or both ends of a cell (known as polar flagellation) or all around the cell in peritrichous flagellation. The spinning of the semi-rigid flagellin filament acts as a screw or a drill to push or pull through the liquid substrate. In polar flagellation clockwise rotation of a flagellum on the left side of a bacterium pulls the bacterium left, and counter clockwise pushes it right. In peritrichous flagellation counter clockwise spinning causes the flagella to wrap around themselves in a bundle to one side and act as a large screw, pushing the bacterium forward. Clockwise rotation causes the bundle to unfurl and the bacteria to rotate randomly (called tumbling). Thus a series of runs and tumbles ensues and the bacterium can move towards or away from a gradient by increasing or decreasing the length of runs. for example in the case of a chemical gradient If the chemical is an attractant runs where the change in chemical level lowers will be short, while runs with a rising chemical gradient will be long. A related method of movement found only in spirochetes are axial filaments: these are composed of between two to more the 100 endoflagella that come out of both ends of the bacteria between the cell membrane and the cell wall. It is thought that rotation of the endoflagella in the perisplasmic space causes the corkscrew shaped outer membrane of the spirochete to rotate, moving the spirochete along. Planktonic bacteria don’t necessarily have to swim to move to different areas of water. Cyanobacteria, for example, use gas vesicles to alter their buoyancy. This enables them to control their depth and so the amount of light they receive. Gas vesicles are spindle shaped hollow structures constructed of protein. The vesicle membrane is about 2nm thick and impermeable to water and solutes but permeable to most gasses. The gas vesicle is formed from two proteins, GvpA, which is arranged in a β sheet formation and makes up 97% of the vesicle. The other 3% is made up of GvpC ribs that strengthen the vesicle. The cytosol of a cell is very viscous for an organism the size of a bacterium, so bacteria that replicate inside the cytosol (as opposed to in separate vesicles) and that must reach a certain position in the cell sequester the actin in the cell for their own use. Bacteria like Listeria monocytogenes stimulate the nucleation of actin monomers behind them, propelling them forward. This leaves a ‘comets tail’ of polymerised actin that depolymerises after about a minute. When a bacterium runs into the plasmallemma it keeps going for a bit, causing a thin extension of the plasma membrane, before bouncing back. Neighbouring cells are liable to engulf the extension, allowing the bacterium to invade the cell without exposing itself to antibodies in the extracellular environment. The mechanism for actin sequestering is not the same in every case, but in the case of L.monocytogenes proteins on the bacterial coat activate ARP complexes which cause the polymerisation. Cells don’t necessarily have to move all of themselves to get where they are going: fungi, for example, just extend hyphae towards the nutrients they are in search of. Hyphae grow from the tip, from bodies known as spitzenkorper, or apical bodies. Positive internal pressure is maintained inside the hypha by active transport of small molecules into the cell to reduce the internal water potential. The tip of the hypha is more plastic then the side walls as lytic vesicle constantly fuse with the cell membrane, softening the chitin wall. Thus the water pressure pushes and stretches out the tip of the hypha. Chitisomes – vesicles containing inactivated chitinase zymogens – also fuse with the plasma membrane, releasing their content. Each chitisome produces a chitin fibre, and the myriad (over 40,000 a minute) of vesicles fusing at the tip keeps building the cell wall as the apical point is extended by hydrostatic pressure. Being able to move from place to place is a highly adaptive trait, and so it is not surprising that all these motility mechanisms, and many more, have evolved to get cells where they are going.

Category:Extremophiles

Extremophiles are organisms that are capable of withstanding extreme environments. Many Archaea are extremophilic. Category:Microbiology

Elchniederung

Die Elchniederung (früher einfach nur Niederung, russisch Losinaja Dolina) ist eine Moorregion im Grenzgebiet zwischen Russland (Oblast Kaliningrad) und Litauen. Nach diesem Gebiet war bis 1945 auch der Landkreis Elchniederung benannt.

Geografie

Nördlich wird sie von der Memel begrenzt, im Westen vom Kurischen Haff, im Süden vom Großen Moosbruch. Die Gegend ist dünn besiedelt, größere Ortschaften sind Slawsk (ehem. Heinrichswalde), Matrossowo (ehem. Gilge) und Bolschakowo (ehem. Groß Skaisgirren) und Jasnoe (ehem. Kukerneese bzw. Kaukehmen).

Verkehr

Durch die Elchniederung führt als Binnenschifffahrtsweg zwischen Pregel und Memel die Matrossowka (Gilgestrom). Alle größeren Orte sind durch Landstraßen miteinander verbunden, wichtigster Verkehrsträger sind Überlandbusse. Es besteht eine Eisenbahnlinie von Sowetsk über Slawsk und Polessk nach Kaliningrad.

Geschichte

Bis zum Zweiten Weltkrieg war die Region durch eine litauischsprachige Minderheit geprägt, die Träger einer reichen Volkskultur war. Hierzu zählt vor allem das reiche Liedgut, welches insbesondere von Laienpredigern mündlich über Generationen hinweg überliefert wurde. Seit dem 18. Jahrhundert gab es Bemühungen, diesen sumpfigen Landstrich durch ausgeklügelte Entwässerungssysteme trocken zu legen. Nach dem Zweiten Weltkrieg verfielen diese Entwässerungssysteme zunehmend. Dies lag zum einen an der Unkenntnis der neuen Bewohner der Elchniederung, die nicht wussten, wie man die Drainagen unterhält, zum Anderen erwiesen sich die in der Sowjetunion eingesetzten schweren landwirtschaftlichen Geräte häufig als ungeeignet für die hier vorkommenden Böden. So wurden viele Entwässerungsrohre durch die schweren Geräte beschädigt und beim Pflügen herausgerissen. In den letzten Jahren ist im heutigen Rajon Slawsk die Entwicklung der Elchniederung von Landflucht und von Versumpfung der in den letzten 200 Jahren trockengelegten Landflächen gekennzeichnet, wodurch viele Ortschaften unbewohnbar wurden. Kategorie:Landschaft in Europa Kategorie:Geographie (Russland)

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Halobacterium

Further reading

External links

Genus

See also

Archaea

History

Archaea, Bacteria and Eukaryotes

Habitats

Form

Evolution and classification

External links

References

Aerobic

Edible salt

History of edible salt

Forms of edible salt

Unrefined salt

Refined salt

Table salt

Health effects

See also

External links

Proteins

Properties of Protein

Structure

Working with proteins

Protein regulation

Diversity

Role of Protein

Functions

Within Nutrition

History

See also

References

External links

Bacteria

History and taxonomy

Metabolism

Movement

Groups and identification

Benefits and dangers

Miscellaneous

See also

References

Further reading

External links

Membranes

Bacteriorhodopsin

External link

Motile

Category:Extremophiles

Elchniederung

Geografie

Verkehr

Geschichte