Bacteria serve as the natural host. Transmission routes are passive diffusion.
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Bacteria and archaea serve as the natural host. Transmission routes are passive diffusion.
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The virus exits the host cell by bacteria lysis. Enterobacteria serve as the natural host. Transmission routes are passive diffusion.
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The virus exits the host cell by lysis, and holin/endolysin/spanin proteins. Bacteria serve as the natural host. Transmission routes are passive diffusion.
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Bacteria serve as the natural host. Transmission routes are passive diffusion. They also use a typical protein primed DNA polymerase for replication, a property shared with the family Tectiviridae.
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As a result, a reservoir can be provided instead of passive diffusion by liberation of growth factors in extended time.Lee, A.C., et al., Experimental Neurology, 2003. 184(1): p. 295-303.
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The United States Naval Research Laboratory developed nanoporous membrane microbial fuel cells that use a non-PEM to generate passive diffusion within the cell. The membrane is a nonporous polymer filter (nylon, cellulose, or polycarbonate). It offers comparable power densities to Nafion (a well known PEM) with greater durability. Porous membranes allow passive diffusion thereby reducing the necessary power supplied to the MFC in order to keep the PEM active and increasing the total energy output.
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Translation takes place by -1 ribosomal frameshifting. The virus exits the host cell by lysis, and holin/endolysin/spanin proteins. Bacteria and archaea serve as the natural host. Transmission route is passive diffusion.
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Ethanol crosses biological membranes and the blood–brain barrier easily, through a simple process of passive diffusion. The volume of distribution of ethanol is around . It is only weakly or not at all plasma protein bound.
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Translation takes place by -1 ribosomal frameshifting, and +1 ribosomal frameshifting. The virus exits the host cell by lysis, and holin/endolysin/spanin proteins. Bacteria and archaea serve as the natural host. Transmission routes are passive diffusion.
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In neuronal cells, an action potential begins with a rush of sodium ions into the cell through sodium channels, resulting in depolarization, while recovery involves an outward rush of potassium through potassium channels. Both of these fluxes occur by passive diffusion.
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Yuavirus is a genus of viruses in the family Siphoviridae, unassigned to a sub-family. Bacteria serve as the natural host, with transmission achieved through passive diffusion. There are currently six species in this genus, including the type species Pseudomonas virus Yua.
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Bcepmuvirus is a genus of viruses in the family Myoviridae, not assigned to a subfamily. Bacteria serve as the natural host, with transmission achieved through passive diffusion. There are currently two species in this genus, including the type species Burkholderia virus BcepMu.
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Naesvirus is a genus of viruses in the family Myoviridae, not assigned to a subfamily. Bacteria serve as the natural host, with transmission achieved through passive diffusion. There are currently five species in this genus, including the type species Burkholderia virus Bcep781.
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Lubbockvirus is a genus of viruses in the family Myoviridae, not assigned to a subfamily. Bacteria serve as the natural host, with transmission achieved through passive diffusion. There are currently three species in this genus, including the type species Clostridium virus phiCD119.
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They hypothesized that this was due to a semipermeable membrane that protected the central nervous system from the passive diffusion of solutes in the bloodstream.Biedl, A; Kraus, R (1898). "Über eine bisher unbekannte toxische Wirkung der Gallensäure auf das Zentralnervensystem". Zentralbl. Inn.
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Hpunavirus (synonyms Hp1likevirus and Hpunalikevirus) is a genus of viruses in the family Myoviridae, within the subfamily Peduovirinae. Bacteria serve as the natural host, with transmission achieved through passive diffusion. There are currently three species in this genus, including the type species Haemophilus phage HP1.
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Felixounavirus (synonyms: FelixO1likevirus, and Felixounalikevirus) is a genus of viruses in the order Caudovirales, in the family Myoviridae. Bacteria serve as natural hosts, with transmission achieved through passive diffusion. There are currently 16 species in this genus, including the type species Salmonella virus FelixO1.
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Psimunavirus (synonyms psiM-like viruses, psiM1-like viruses, Psimunalikevirus) is a genus of viruses in the family Siphoviridae. Bacteria and archaea serve as the natural host, with transmission achieved through passive diffusion. There is currently one species in this genus: the type species Psimunavirus psiM2.
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Ravinvirus (synonym N15-like viruses, N15likevirus) is a genus of viruses in the order Caudovirales, in the family Siphoviridae. Bacteria serve as natural hosts, with transmission achieved through passive diffusion. There is currently only one species in this genus: the type species Escherichia virus N15.
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Bixzunavirus (synonyms: I3-likeviruses and I3likevirus) is a genus of viruses in the order Caudovirales, in the family Myoviridae. Bacteria serve as natural hosts, with transmission achieved through passive diffusion. There are currently eight species in this genus, including the type species Mycobacterium virus I3.
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Tequatrovirus is a genus of viruses in the order Caudovirales, in the family Myoviridae, in the subfamily Tevenvirinae. Gram-negative bacteria serve as the natural host, with transmission achieved through passive diffusion. There are currently 21 species in this genus, including the type species Escherichia virus T4.
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Lederbergvirus (synonyms P22-like viruses, P22-like phages, P22likevirus) is a genus of virusesin the order Caudovirales, in the family Podoviridae. Bacteria serve as natural hosts, with transmission achieved through passive diffusion. There are currently six species in this genus, including the type species Salmonella virus P22.
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Hapunavirus (synonyms: Hap1likevirus and Hapunalikevirus) is a genus of viruses in the family Myoviridae, not assigned to a subfamily. Bacteria serve as the natural host, with transmission achieved through passive diffusion. There are currently two species in this genus, including the type species Halomonas virus phiHAP-1.
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Zindervirus (synonym SP6-like viruses, Sp6likevirus) is a genus of viruses in the family Autographiviridae, within the subfamily Molineuxvirinae. Bacteria serve as the natural host, with transmission achieved through passive diffusion. There are currently three species in this genus, including the type species Salmonella virus SP6.
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Tequintavirus (synonyms T5-like phages, T5-like viruses, T5likevirus) is a genus of viruses in the order Caudovirales, in the family Demerecviridae. Bacteria serve as the natural host, with transmission achieved through passive diffusion. There are currently 22 species in this genus, including the type species Escherichia virus T5.
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Muvirus (synonyms: Mu-like phages, Mu-like viruses, Mulikevirus) is a genus of viruses in the order Caudovirales, in the family Myoviridae. Bacteria serve as natural hosts, with transmission achieved through passive diffusion. There are currently two species in this genus, including the type species Escherichia virus Mu.
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Fromanvirus (synonyms L5-like viruses, L5-like phages, L5likevirus) is a genus of viruses in the order Caudovirales, in the family Siphoviridae. Bacteria serve as natural hosts, with transmission achieved through passive diffusion. There are currently 59 species in this genus, including the type species Mycobacterium virus L5.
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These proteins may include sodium-potassium-2 chloride co-transporter, chloride anion exchangers, and chloride channels. As a result of the reduce activity in these transporters, another suggested mechanism is a depletion in concentration gradient which would allow for the passive diffusion of chloride in and out the tubule.
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Ceduovirus (synonyms c2-like viruses, c2-like phages, C2likevirus) is a genus of viruses in the family Siphoviridae, unassigned to a sub-family. Bacteria serve as the natural host, with transmission achieved through passive diffusion. There are currently two species in this genus, including the type species Lactococcus virus c2.
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Rosenblumvirus (synonyms: AHJD-like viruses, Ahjdlikevirus) is a genus of viruses in the order Caudovirales, in the family Podoviridae, in the subfamily Picovirinae. Gram positive bacteria serve as natural hosts, with transmission achieved through passive diffusion. There are currently 12 species in this genus, including the type species Staphylococcus virus 44AHJD.
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The blood–brain barrier is formed by special tight junctions between endothelial cells lining brain blood vessels. Blood vessels of all tissues contain this monolayer of endothelial cells, however only brain endothelial cells have tight junctions preventing passive diffusion of most substances into the brain tissue.Neuroscience, Purves et al. Sinauer Associates, Inc. 2008.
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Lambdavirus (synonyms Lambda-like viruses, Lambda-like phages, Lambda phage group, Lambda phage) is a genus of viruses in the order Caudovirales, in the family Siphoviridae. Bacteria serve as natural hosts, with transmission achieved through passive diffusion.. There are currently four species in this genus, including the type species Escherichia virus Lambda.
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Thiamine is released by the action of phosphatase and pyrophosphatase in the upper small intestine. At low concentrations, the process is carrier-mediated. At higher concentrations, absorption also occurs via passive diffusion. Active transport is greatest in the jejunum and ileum, but it can be inhibited by alcohol consumption or by folate deficiency.
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Peduovirus (also known as P2-like phages and P2-like viruses) is a genus of viruses in the order Caudovirales, in the family Myoviridae, in the subfamily Peduovirinae. Bacteria serve as natural hosts, with transmission achieved through passive diffusion. There are currently 6 species in this genus, including the type species Escherichia virus P2.
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A sucrose specific porin from Salmonella typhimurium, a gram-negative bacterium. Porins are beta barrel proteins that cross a cellular membrane and act as a pore, through which molecules can diffuse. Unlike other membrane transport proteins, porins are large enough to allow passive diffusion, i.e., they act as channels that are specific to different types of molecules.
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The thin ascending limb is impermeable to water; but is permeable to ions allowing for some sodium reabsorption. Na/K-ATPase is expressed at very low levels in this segment and thus this reabsorption is likely through passive diffusion. Salt moves out of the tubule and into the interstitium due to osmotic pressure created by the countercurrent system.
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These are then released into the interstitial fluids surrounding the cells that have manufactured the eicosanoid hormone. If arachidonate is acted upon by a lipoxygenase instead of cyclooxygenase, Hydroxyeicosatetraenoic acids and leukotrienes are formed. They also act as local hormones. Prostaglandins were originally believed to leave the cells via passive diffusion because of their high lipophilicity.
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Toxins and toxicants can move through the layers by passive diffusion. The stratum corneum is the outermost layer of the epidermis and the rate-limiting barrier in absorption of an agent. Thus, how quickly something passes through this thicker outer layer determines the overall absorption. The stratum corneum is primarily composed of lipophilic cholesterol, cholesterol esters and ceramides.
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Teseptimavirus (synonyms T7 phage group, T7-like phages, T7-like viruses, T7likevirus) is a genus of viruses in the order Caudovirales, in the family Autographiviridae, in the subfamily Studiervirinae. Bacteria serve as the natural host, with transmission achieved through passive diffusion. There are currently 17 species in this genus, including the type species Escherichia virus T7.
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Food B12 is absorbed by two processes. The first is a vitamin B12-specific intestinal mechanism using intrinsic factor through which 1–2 micrograms can be absorbed every few hours, by which most food consumption of the vitamin is absorbed. The second is a passive diffusion process. The human physiology of active vitamin B12 absorption from food is complex.
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Passive diffusion on a cell membrane. However; in a case of auxins, only the non-dissociated portion of auxin molecules is able to cross the membrane As weak acids, the protonation state of auxins is dictated by the pH of the environment; a strongly acidic environment inhibits the forward reaction (dissociation), whereas an alkaline environment strongly favors it (see Henderson-Hasselbalch equation): The export of auxins from cells is termed auxin efflux and the entry of auxin in to cells is called auxin influx. The first step in polar transport is auxin influx. Auxin enters plant cells by two methods, first by passive diffusion as non-ionized IAA molecule or the protonated form as IAAH across the phospholipid bilayer, or second by active co-transport in the anionic form IAA−.
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The lactone ring in CPT is highly susceptible to hydrolysis. The open ring form is inactive and it must therefore be closed to inhibit topoisomerase I. The closed form is favored in acidic condition, as it is in many cancer cells microenvironment. CPT is transported into the cell by passive diffusion. Cellular uptake is favored by lipophilicity, which enhances intracellular accumulation.
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Pantetheinase, an intestinal enzyme, then hydrolyzes pantetheine into free pantothenic acid. Free pantothenic acid is absorbed into intestinal cells via a saturable, sodium-dependent active transport system. At high levels of intake, when this mechanism is saturated, some pantothenic acid may also be additionally absorbed via passive diffusion. As a whole, when intake increases 10-fold, absorption rate decreases to 10%.
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The hairpin contains four basic residues that enable passive diffusion across the membrane. Two features of the protein structure have been associated with cell-penetrating properties that are uncommon for peptide toxins. Firstly, a patch (or predominance) of basic residues is located at the open end of the hairpin, where the amino- and carboxy-terminal meet. Secondly, the amino-terminal in WaTx exhibits a dense dipole moment.
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The smallest tubes, tracheoles, penetrate cells and serve as sites of diffusion for water, oxygen, and carbon dioxide. Gas may be conducted through the respiratory system by means of active ventilation or passive diffusion. Unlike vertebrates, insects do not generally carry oxygen in their haemolymph. A tracheal tube may contain ridge-like circumferential rings of taenidia in various geometries such as loops or helices.
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The carbon used to form the majority of the lipid is from acetyl-CoA, which is the decarboxylation product of pyruvate. Pyruvate may enter the plastid from the cytosol by passive diffusion through the membrane after production in glycolysis. Pyruvate is also made in the plastid from phosphoenolpyruvate, a metabolite made in the cytosol from pyruvate or PGA. Acetate in the cytosol is unavailable for lipid biosynthesis in the plastid.
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Nucleoporins are only required for the transport of large hydrophilic molecules above 40 kDa, as smaller molecules pass through nuclear pores via passive diffusion. Nucleoporins play an important role in the transport of mRNA from the nucleus to the cytoplasm after transcription. Depending on their function, certain nucleoporins are localized to either the cytosolic or nucleoplasmic side of the nuclear pore complex. Other nucleoporins may be found on both sides.
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The permeability of a membrane is the rate of passive diffusion of molecules through the membrane. These molecules are known as permeant molecules. Permeability depends mainly on the electric charge and polarity of the molecule and to a lesser extent on the molar mass and size of the molecule. Due to the cell membrane's internal hydrophobic structure, small electrically neutral molecules pass through the membrane more easily than charged, large ones.
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These algae blooms collapse usually after 5–8 days and several studies have shown that bloom termination is intrinsically linked to infection by coccolithoviruses.Wilson WH, Tarran GA, Schroeder D, Cox M, Oke J, Malin G. (2002) Isolation of viruses responsible for the demise of an Emiliania huxleyi bloom in the English Channel. Journal of the Marine Biological Association of the United Kingdom 82:369–377. Transmission of viruses between algal hosts occurs via passive diffusion.
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It is known that ethion is small and lipophilic molecule and because it has these characteristics rapid absorption across cell membranes is expected. This absorption from skin, lungs and the gut to the blood will happen via passive diffusion. Furthermore, ethion is changed in the liver, via desulfuration, into its active metabolite: ethion monoxon. Due to this change happening in the liver the primary place of damage it expected to be the liver.
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Lipid bilayers are generally impermeable to ions and polar molecules. The arrangement of hydrophilic heads and hydrophobic tails of the lipid bilayer prevent polar solutes (ex. amino acids, nucleic acids, carbohydrates, proteins, and ions) from diffusing across the membrane, but generally allows for the passive diffusion of hydrophobic molecules. This affords the cell the ability to control the movement of these substances via transmembrane protein complexes such as pores, channels and gates.
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Estradiol is rapidly distributed throughout the body, with a distribution phase of about 6 minutes following intravenous injection. Estradiol is taken up into cells via passive diffusion due to its lipophilicity. Due to binding to the ERs, estradiol is preferentially concentrated in tissues with the highest ER content. In animals, these tissues have included the uterus, vagina, mammary glands, pituitary gland, hypothalamus, other brain regions, adipose tissue, liver, and adrenal glands, among other tissues.
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Both niacin and niacinamide are rapidly absorbed from the stomach and small intestine. Absorption is facilitated by sodium-dependent diffusion, and at higher intakes, via passive diffusion. Unlike some other vitamins, the percent absorbed does not decrease with increasing dose, so that even at amounts of 3-4 grams, absorption is nearly complete. With a one gram dose, peak plasma concentrations of 15 to 30 μg/mL are reached within 30 to 60 minutes.
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Hydroxocobalamin injection is a clear red liquid solution. B12 can be supplemented by pill or injection and appears to be equally effective in those with low levels due to deficient absorption of B12. When large doses are given by mouth its absorption does not rely on the presence of intrinsic factor or an intact ileum. Instead, these large-dose supplements result in 1% to 5% absorption along the entire intestine by passive diffusion.
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The tracheae are invaginations of the cuticular exoskeleton that branch (anastomose) throughout the body with diameters from only a few micrometres up to 0.8 mm. Diffusion of oxygen and carbon dioxide takes place across the walls of the smallest tubes, called tracheoles, which penetrate tissues and even indent individual cells. Gas may be conducted through the respiratory system by means of active ventilation or passive diffusion. Unlike vertebrates, insects do not generally carry oxygen in their haemolymph.
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Serum levels of carotenoids vary between region, ethnicity, and sex in the healthy population. All are absorbed by passive diffusion from the gastrointestinal tract and are then partially metabolized in the intestinal mucosa and liver to vitamin A. From there they are transported in the plasma into the peripheral tissues. Carotenoids are eliminated via sweat, sebum, urine, and gastrointestinal secretions. Carotenoids contribute to normal- appearing human skin color, and are a significant component of physiologic ultraviolet photoprotection.
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The high abundance of ladderane lipids in the anammoxosome results in an exceptionally dense membrane with reduced permeability. The reduced permeability may decrease the passive diffusion of protons across the membrane that would dissipate the electrochemical gradient. This would be especially detrimental to anammox bacteria, due to the relatively slow anammox metabolism. The decreased permeability has also been hypothesized to sequester the highly toxic and mutagenic intermediates, hydrazine and hydroxylamine, which can readily diffuse through biomembranes.
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Extracellular Phototropic Digestion is a process in which saprobionts feed by secreting enzymes through the cell membrane onto the food. The enzymes catalyze the digestion of the food into molecules small enough to be taken up by passive diffusion, transport, osmotrophy or phagocytosis. Since digestion occurs outside the cell, it is said to be extracellular. It takes place either in the lumen of the digestive system, in a gastric cavity or other digestive organ, or completely outside the body.
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Whereas free steroids like estradiol are lipophilic and can enter cells via passive diffusion, steroid conjugates like E1S are hydrophilic and are unable to do so. Instead, steroid conjugates require active transport via membrane transport proteins to enter cells. Studies in animals and humans have had mixed findings on uptake of exogenously administered E1S in normal and tumorous mammary gland tissue. This is in contrast to substantial uptake of exogenously administered estradiol and estrone by the mammary glands.
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The drug is absorbed in the small intestine, primarily in the duodenum and jejunum. Absorption occurs via a controlled, active mechanism. No passive diffusion takes place, which ensures that practically no unbound (to transferrin) iron reaches the blood. The absorbed iron is primarily stored in the liver as ferritin (protein used for iron storage) and subsequently made available to the body for various functions, primarily for incorporation into the red blood cells' hemoglobin, thereby transporting oxygen in the blood.
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Nanotechnology is under preliminary research for its potential to facilitate the transfer of drugs across the BBB. Capillary endothelial cells and associated pericytes may be abnormal in tumors and the blood-brain barrier may not always be intact in brain tumors. Other factors, such as astrocytes, may contribute to the resistance of brain tumors to therapy using nanoparticles. Fat soluble molecules less than 400 Daltons in weight can freely diffuse past the BBB through lipid mediated passive diffusion.
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The large intestine absorbs some of the products formed by the bacteria inhabiting this region. Undigested polysaccharides (fiber) are metabolized to short-chain fatty acids by bacteria in the large intestine and absorbed by passive diffusion. The bicarbonate that the large intestine secretes helps to neutralize the increased acidity resulting from the formation of these fatty acids. These bacteria also produce large amounts of vitamins, especially vitamin K and biotin (a B vitamin), for absorption into the blood.
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Therefore, the authors developed a new method to fabricate functional, cell-lining and perfusable microchannels inside 3D hydrogel. The vessel endothelial and renal epithelial cells are cultured inside hydrogel microchannel and form cellular coverage to mimic vessels and tubules, respectively. They employed confocal microscope to examine the passive diffusion of one small organic molecule (usually drugs) between the vessels and tubules in hydrogel. The study demonstrates the beneficial potential to mimic renal physiology for regenerative medicine and drug screening.
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Phenanthriplatin is thought to penetrate cell membranes in its ionised form by either passive diffusion or carrier-mediated active transport. The hydrophobic phenanthridine ligand of the drug is thought to maximise its cellular uptake, rendering it more effective and cytotoxic compared with cisplatin. Once it has entered the cell, phenanthriplatin is distributed in a similar manner to other platinum- based anticancer agents, residing primarily in the cell's nucleus. The ultimate target of the drug is nuclear DNA.
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Uptake of thiamine by cells of the blood and other tissues occurs via active transport and passive diffusion. About 80% of intracellular thiamine is phosphorylated and most is bound to proteins. Two members of the SLC gene family of transporter proteins, SLC19A2 and SLC19A3, are capable of the thiamine transport. In some tissues, thiamine uptake and secretion appears to be mediated by a soluble thiamine transporter that is dependent on Na+ and a transcellular proton gradient.
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This increase in sensitivity is mediated by a 100-fold increase in ERs, as well as other mechanisms such as changes in coactivator sensitivity and degree of phosphorylation of transactivation factors. Progestogens like progesterone and androgens like testosterone downregulate the ERs in certain tissues such as the endometrium and breasts, among others. Estradiol is a steroid and a lipophilic compound. As a result, it readily enters cells via simple passive diffusion through the lipid bilayer of the cell membrane.
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Perforin is a pore forming cytolytic protein found in the granules of cytotoxic T lymphocytes (CTLs) and natural killer cells (NK cells). Upon degranulation, perforin binds to the target cell's plasma membrane, and oligomerises in a Ca2+ dependent manner to form pores on the target cell. The pore formed allows for the passive diffusion of a family of pro-apoptotic proteases, known as the granzymes, into the target cell. The lytic membrane-inserting part of perforin is the MACPF domain.
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Viral replication is nucleo-cytoplasmic. Replication follows the DNA strand displacement model, and DNA-templated transcription is the method of transcription. The virus exits the host cell by lysis via lytic phospholipids, with passive diffusion being the mechanism behind transmission routes. In three dimensional recreations of PBCV-1 (Paramecium bursaria chlorella virus), a prototype of chlorovirus, it is seen that the spike first contacts the host’s cell wall and is aided by fibres in order to secure the virus to the host.
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Joseph Barcroft, in 1920, spent six days in a sealed glass chamber to investigate respiration at altitude. The partial pressure of oxygen was initially 163 mmHg falling to 84 mmHg (equivalent to an altitude of 18,000 ft) as the experiment progressed. Barcroft was attempting to disprove a theory of John Scott Haldane that the lungs actively secrete oxygen into the blood (rather than just through the process of passive diffusion) under conditions of low oxygen partial pressure. Barcroft suffered from severe hypoxia.
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The possible presence of water molecules in the pore lumen calls for a reassessment of the notion that Amt/Rh proteins work as plain NH3 channels. Indeed, functional experiments on plant ammonium transporters and Rh proteins suggest a variety of permeation mechanisms including the passive diffusion of NH3, the antiport of NH4+/H+, the transport of NH4+, or the cotransport of NH3/H+. Lamoureux et al. discuss these mechanisms in light of functional and simulation studies on the AmtB transporter.
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Passive diffusion across a cell membrane. Passive transport is a movement of ions and other atomic or molecular substances across cell membranes without need of energy input. Unlike active transport, it does not require an input of cellular energy because it is instead driven by the tendency of the system to grow in entropy. The rate of passive transport depends on the permeability of the cell membrane, which, in turn, depends on the organization and characteristics of the membrane lipids and proteins.
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WaTx penetrates the plasma membrane instead of following standard routes, subsequently accessing the inferior part of the cell. The basic residues and dipole moment on the helical hairpin structure enable the passive diffusion of WaTx. Once the toxin arrives in the cell, it activates TRPA1 via an intracellular domain in the lower part of voltage-sensing segments S1-S4 called ‘the allosteric nexus’. The allosteric nexus is located at the region where the TRP-like domain, pre-S1 helix and cysteine-rich S4-S5 linker meet.
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Electrical coupling among cardiac cells is crucial for a healthy heart, allowing the cardiac muscle fibers to contract normally. This coupling is done by gap junctions. Gap junctions permit the passive diffusion of materials–such as ions–across the cytoplasm of one cell to another; this junction enables proper propagation of electrical impulses along cardiac cells. The genetic cardiac disease, Arrhythmogenic Cardiomyopathy (ACM), is marked by the reduced expression/number of the heart’s gap junctions, which can further lead to impaired function and ventricular arrhythmia.
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Main article: Clinical significance in Blood-brain barrier One main challenge for developing new PET tracers for neuroimaging is that these tracers must cross the blood-brain barrier. Commonly, small molecules which are fat soluble have been used as they can pass the blood-brain barrier through lipid mediated passive diffusion. However, as pharmaceutics move towards large biomolecules for therapies, new research has also focused on using biomolecules, such as antibodies, for PET tracers. These new larger PET tracers have increased difficulty passing the BBB as they are too large to passively diffuse across.
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The inside/outside discontinuity at the cell surface enabled by a lipid bilayer membrane (capacitor) is at the core of bioelectricity. The plasma membrane was an indispensable structure for the origin and evolution of life itself. It provided compartmentalization permitting the setting of a differential voltage/potential gradient (battery or voltage source) across the membrane, probably allowing early and rudimentary bioenergetics that fueled cell mechanisms. During evolution, the initially purely passive diffusion of ions (charge carriers), become gradually controlled by the acquisition of ion channels, pumps, exchangers, and transporters.
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Although oral megadoses and intramuscular injections are the most common methods of treatment currently available, several novel methods are being tested, with high promise for future incorporation into mainstream treatment methods. As injections are unfavourable vehicles for drug delivery, current research involves improving the passive diffusion across the ileum upon oral ingestion of cobalamin derivatives. Researchers have recently taken advantage of the novel compound sodium N-[8-(2-hydroxybenzoyl)amino]caprylate (SNAC), which greatly enhances both bioavailability and metabolic stability. SNAC is able to form a noncovalent complex with cobalamin while preserving its chemical integrity.
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The passive diffusion process of B12 absorption—normally a very small portion of total absorption of the vitamin from food consumption—may exceed the R-protein and IF mediated absorption when oral doses of B12 are very large (a thousand or more µg per dose) as commonly happens in dedicated-pill oral B12 supplementation. This allows pernicious anemia and certain other defects in B12 absorption to be treated with oral megadoses of B12, even without any correction of the underlying absorption defects. See the section on supplements above.
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Vitamin B6 is absorbed in the jejunum and ileum by passive diffusion. With the capacity for absorption being so great, animals are able to absorb quantities much greater than necessary for physiological demands. The absorption of pyridoxal phosphate and pyridoxamine phosphate involves their dephosphorylation catalyzed by a membrane-bound alkaline phosphatase. Those products and nonphosphorylated forms in the digestive tract are absorbed by diffusion, which is driven by trapping of the vitamin as 5′-phosphates through the action of phosphorylation (by a pyridoxal kinase) in the jejunal mucosa.
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To perform a test, the sample in question is mixed with a buffer specific to the RSID test. The sample is then deposited onto the sample window where it is pulled through the test and control regions by a paper wick via passive diffusion. The RSID unit is impregnated with fluid-specific antibodies conjugated to colored complexes that will re-dissolve and diffuse at this time. If the fluid in question is present in the questioned sample, antibodies at the test line will react to the colored antibody complexes and form a colored line.
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Prostaglandins were originally believed to leave the cells via passive diffusion because of their high lipophilicity. The discovery of the prostaglandin transporter (PGT, SLCO2A1), which mediates the cellular uptake of prostaglandin, demonstrated that diffusion alone cannot explain the penetration of prostaglandin through the cellular membrane. The release of prostaglandin has now also been shown to be mediated by a specific transporter, namely the multidrug resistance protein 4 (MRP4, ABCC4), a member of the ATP-binding cassette transporter superfamily. Whether MRP4 is the only transporter releasing prostaglandins from the cells is still unclear.
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Metformin has acid dissociation constant values (pKa) of 2.8 and 11.5, so exists very largely as the hydrophilic cationic species at physiological pH values. The metformin pKa values make it a stronger base than most other basic medications with less than 0.01% nonionized in blood. Furthermore, the lipid solubility of the nonionized species is slight as shown by its low logP value (log(10) of the distribution coefficient of the nonionized form between octanol and water) of −1.43. These chemical parameters indicate low lipophilicity and, consequently, rapid passive diffusion of metformin through cell membranes is unlikely.
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Such a concentration gradient across a semipermeable membrane sets up an osmotic flow for the water. Osmosis, in biological systems involves a solvent, moving through a semipermeable membrane similarly to passive diffusion as the solvent still moves with the concentration gradient and requires no energy. While water is the most common solvent in cell, it can also be other liquids as well as supercritical liquids and gases. 2\. Transmembrane protein channels and transporters: Transmembrane proteins extend through the lipid bilayer of the membranes; they function on both sides of the membrane to transport molecules across it.
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It elicits a warm and pungent flavour. The in vitro biological activity of polygodial has been reported in the scientific literature to include antifungal and antimicrobial activities, antihyperalgesia, potent attachment-inhibitory activity, insect antifeedant activity, antinociception, vasorelaxing action in vessels of rabbit and guinea pig, anti-inflammatory and antiallergic activities. Polygodial’s primary antifungal action is as a nonionic surfactant, disrupting the lipid-protein interface of integral proteins nonspecifically, denaturing their functional conformation. It is also likely that polygodial permeates by passive diffusion across the plasma membrane, and once inside the cells may react with a variety of intracellular compounds.
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The mechanism of mineral formation in bone is clearly distinct from the phylogenetically older process by which cartilage is mineralized: tetracycline does not label mineralized cartilage at narrow bands or in specific sites, but diffusely, in keeping with a passive mineralization mechanism. Osteoblasts separate bone from the extracellular fluid by tight junctions by regulated transport. Unlike in cartilage, phosphate and calcium cannot move in or out by passive diffusion, because the tight osteoblast junctions isolate the bone formation space. Calcium is transported across osteoblasts by facilitated transport (that is, by passive transporters, which do not pump calcium against a gradient).
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Peepers are passive diffusion samplers used for metals in freshwater and marine sediment pore water, so they can be used to find areas that may have metal-contaminated sediments. Peepers are plastic vessels filled with clean water and covered in a dialysis membrane, which allows metals in sediment pore water to enter the water inside the peeper. They are usually placed deep enough into sediment to be in an anoxic environment, in which metals will be soluble enough to sample. If the peepers are deployed long enough so the sediment pore water and contained peeper water reach equilibrium, they can accurately provide metal concentrations in sampled sediment pore water.
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Some species of diving beetles (Dytiscidae) carry a bubble of air with them whenever they dive beneath the water surface. This bubble may be held under the elytra or it may be trapped against the body using specialized hairs. The bubble usually covers one or more spiracles so the insect can breathe air from the bubble while submerged. An air bubble provides an insect with only a short-term supply of oxygen, but thanks to its unique physical properties, oxygen will diffuse into the bubble and displacing the nitrogen, called passive diffusion, however the volume of the bubble eventually diminishes and the beetle will have to return to the surface.
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Injection of hydroxocobalamin is often used if digestive absorption is impaired, but this course of action may not be necessary with high-dose oral supplements (such as 0.5–1.0mg or more), because with large quantities of the vitamin taken orally, even the 1% to 5% of the free crystalline B12 that is absorbed along the entire intestine by passive diffusion may be sufficient to provide a necessary amount. A person with cobalamin C disease (which results in combined methylmalonic aciduria and homocystinuria) may require treatment with intravenous or intramuscular hydroxocobalamin or transdermal B12, because oral cyanocobalamin is inadequate in the treatment of cobalamin C disease.
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The microdialysis technique requires the insertion of a small microdialysis catheter (also referred to as microdialysis probe) into the tissue of interest. The microdialysis probe is designed to mimic a blood capillary and consists of a shaft with a semipermeable hollow fiber membrane at its tip, which is connected to inlet and outlet tubing. The probe is continuously perfused with an aqueous solution (perfusate) that closely resembles the (ionic) composition of the surrounding tissue fluid at a low flow rate of approximately 0.1-5μL/min. Once inserted into the tissue or (body)fluid of interest, small solutes can cross the semipermeable membrane by passive diffusion.
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Non- electrolytes, substances that generally are hydrophobic and lipophilic, usually pass through the membrane by dissolution in the lipid bilayer, and therefore, by passive diffusion. For those non-electrolytes whose transport through the membrane is mediated by a transport protein the ability to diffuse is, generally, dependent on the partition coefficient K. Partially charged non-electrolytes, that are more or less polar, such as ethanol, methanol or urea, are able to pass through the membrane through aqueous channels immersed in the membrane. There is no effective regulation mechanism that limits this transport, which indicates an intrinsic vulnerability of the cells to the penetration of these molecules.
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Passive diffusion on a cell membrane. Diffusion is the net movement of material from an area of high concentration to an area with lower concentration. The difference of concentration between the two areas is often termed as the concentration gradient, and diffusion will continue until this gradient has been eliminated. Since diffusion moves materials from an area of higher concentration to an area of lower concentration, it is described as moving solutes "down the concentration gradient" (compared with active transport, which often moves material from area of low concentration to area of higher concentration, and therefore referred to as moving the material "against the concentration gradient").
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In eukaryotic cells the pyruvate decarboxylation occurs inside the mitochondrial matrix, after transport of the substrate, pyruvate, from the cytosol. The transport of pyruvate into the mitochondria is via the transport protein pyruvate translocase. Pyruvate translocase transports pyruvate in a symport fashion with a proton, and hence is active, consuming energy.. Alternative sources say "transport of pyruvate across the outer mitochondrial membrane appears to be easily accomplished via large non- selective channels such as voltage-dependent anion channels, which enable passive diffusion" and transport across inner mitochondrial membrane is mediated by mitochondrial pyruvate carrier 1 (MPC1) and mitochondrial pyruvate carrier 2 (MPC2) . Upon entry to the mitochondria, the pyruvate is decarboxylated, producing acetyl-CoA.
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The device's design requirements would require the filtration fraction in the glomerulus to vary between 15–20%, or the filtration reabsorption in the proximal convoluted tubule to vary between 65–70%, and finally the urea concentration in urine (collected at one of the two outlets of the device) to vary between 200–400 mM. One recent report illustrates a biomimic nephron on hydrogel microfluidic devices with establishing the function of passive diffusion. The complex physiological function of nephron is achieved on the basis of interactions between vessels and tubules (both are hollow channels). However, conventional laboratory techniques usually focus on 2D structures, such as petri-dish that lacks capability to recapitulate real physiology that occurs in 3D.
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Consequently, pyoverdine has become a model trait to study microbial cooperation and exploitation. In P. aeruginosa, pyoverdine non-producing “cheat” bacteria have been shown to i) evolve readily from a producing ancestor; and ii) outcompete cooperating strains in mixed culture in a density- and frequency-dependent manner. Since pyoverdine usage relies on passive diffusion and pyoverdine production is metabolically costly, environmental conditions are known to influence the likelihood of successful exploitation. The competitive advantage of pyoverdine non-producers over producers in mixed culture was shown to be maximized when environments are well-mixed and molecules diffuse readily (low spatial structure) and when the costs and benefits of pyoverdine production are high, i.e.
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The addition of molecules like formaldehyde, paraformaldehyde, or glutaraldehyde can facilitate attachment of the scaffolding to the proteins and nucleic acids that are to be preserved, and the addition of heat is necessary to establish the actual linkages between the cellular components and the acrylamide. Once this step is complete, the protein and nucleic acid components of the target tissue's cells are held firmly in place, while the lipid components remain detached. Lipids are then removed over 1–2 weeks of passive diffusion in detergent, or accelerated by electrophoretic methods to only hours to days. As they pass through, the detergent's lipophilic properties enable it to pick up and excise any lipids encountered along the way.
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Algae such as diatoms, along with other phytoplankton, are photosynthetic primary producers supporting the food web of the Great Lakes, and have been effected by global warming. The changes in the size or in the function of the primary producers may have a direct or an indirect impact on the food web. Photosynthesis carried out by diatoms comprises about one fifth of the total photosynthesis. By taking out of the water, to photosynthesize, diatoms help to stabilize the pH of the water, as otherwise would react with water making it more acidic. :CO2 + H2O <=> HCO3^- + H+ Diatoms acquire inorganic carbon thought passive diffusion of and HCO3, as well they use carbonic anhydrase mediated active transport to speed up this process.
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Estradiol is a highly potent compound and circulates at picomolar concentrations (pg/mL), which makes it ideal for transdermal application as only small amounts of substance need to be delivered across the skin. Conversely, progesterone, which circulates at levels in the nanomolar range and requires a far higher quantity of substance for biological effect, is not well-suited for transdermal delivery. Fatty acid esters of estradiol, such as estradiol benzoate, estradiol valerate, and estradiol cypionate, have been found to have similar estrogenic potency to estradiol but a comparatively longer duration with transdermal administration in animal studies. Regardless of administration form, such as patch or gel, transdermal estradiol is transported into the skin, including through the stratum corneum, epidermis, and dermis, by a passive diffusion process.
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The blood–brain barrier (BBB) is a highly selective semipermeable border of endothelial cells that prevents solutes in the circulating blood from non- selectively crossing into the extracellular fluid of the central nervous system where neurons reside. The blood-brain barrier is formed by endothelial cells of the capillary wall, astrocyte end-feet ensheathing the capillary, and pericytes embedded in the capillary basement membrane. This system allows the passage of some molecules by passive diffusion, as well as the selective transport of various nutrients, ions, organic anions, and macromolecules such as glucose, water and amino acids that are crucial to neural function. The blood-brain barrier restricts the passage of pathogens, the diffusion of solutes in the blood, and large or hydrophilic molecules into the cerebrospinal fluid, while allowing the diffusion of hydrophobic molecules (O2, CO2, hormones) and small polar molecules.
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The USGS also looked at how the land was historically used so that a correlation could be drawn between locations of high concentrations of chemicals and the source polluters. Scientists used passive-diffusion bag samplers to collect pore water from Cypress Creek and groundwater from other locations, which would provide data and concentration levels of the contaminants in the creek. Scientists also took tissue samples from trees that were growing along the Alabama River, Cypress Creek, and downtown Montgomery so that the analysis and data could give a better idea of the big picture and the true reach of the pollution. The tests concluded that the aquifer residing below the Capital City Plume site was contaminated with perchloroethylene (PCE) and trichloroethylene (TCE) and that the contamination was likely caused by the commercial printing industry that resided in downtown Montgomery in the late 1800s and early 1900s.
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