query: where does facilitated diffusion occur in the cell membrane

pos: Facilitated diffusion retinol binding protein). The metabolites are not altered because no energy is required for facilitated diffusion. Only permease changes its shape in order to transport metabolites. The form of transport through a cell membrane in which a metabolite is modified is called group translocation transportation. Glucose, sodium ions, and chloride ions are just a few examples of molecules and ions that must efficiently cross the plasma membrane but to which the lipid bilayer of the membrane is virtually impermeable. Their transport must therefore be "facilitated" by proteins that span the membrane and provide an alternative route or bypass mechanism. Various

neg: Passive transport Passive transport 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. The four main kinds of passive transport are simple diffusion, facilitated diffusion, filtration, and/or osmosis. Diffusion is the net movement of material

neg: Facilitated diffusion Facilitated diffusion Facilitated diffusion (also known as facilitated transport or passive-mediated transport) is the process of spontaneous passive transport (as opposed to active transport) of molecules or ions across a biological membrane via specific transmembrane integral proteins. Being passive, facilitated transport does not directly require chemical energy from ATP hydrolysis in the transport step itself; rather, molecules and ions move down their concentration gradient reflecting its diffusive nature. Facilitated diffusion is different from simple diffusion in several ways. First, the transport relies on molecular binding between the cargo and the membrane-embedded channel or carrier protein. Second, the rate of facilitated

neg: Hop diffusion free diffusion, which occurs inside cell membrane compartments, and infrequent intercompartmental transitions (hops). The complexity of this type of anomalous diffusion is further enhanced due to an inherent broad distribution of compartment sizes. Hop diffusion Hop diffusion - is a non-Brownian diffusion of proteins and lipid molecules within the plasma membrane. Hop diffusion occurs due to the discontinuity of the cell cytoplasmic membrane. According to the Fences and pickets model, plasma membrane is compartmentalized by actin-based membrane-skeleton “fences”, that occur when cytoplasmic domains collide with the actin-based membrane skeleton; and anchored-transmembrane protein “pickets”. Due to these obstacles membrane proteins undergo

neg: Hop diffusion Hop diffusion Hop diffusion - is a non-Brownian diffusion of proteins and lipid molecules within the plasma membrane. Hop diffusion occurs due to the discontinuity of the cell cytoplasmic membrane. According to the Fences and pickets model, plasma membrane is compartmentalized by actin-based membrane-skeleton “fences”, that occur when cytoplasmic domains collide with the actin-based membrane skeleton; and anchored-transmembrane protein “pickets”. Due to these obstacles membrane proteins undergo temporary confinement within 30–700- nm compartments with infrequent intercompartmental hops. Hops between adjacent compartments presumably occur due to: While simple Brownian diffusion is isotropic and homogeneous, hop diffusion is more complex and combines

neg: Facilitated diffusion cell could be rapid or slow depending on the number of membrane-spanning protein. It is transported against the concentration gradient by a dependent glucose symporter which provides a driving force to other glucose molecules in the cells. Facilitated diffusion helps in the release of accumulated glucose into the extracellular space adjacent to the blood capillary. Carbon monoxide has a facilitated diffusion process similar to that of oxygen. They both make use of the high affinity of hemoglobin and myoglobin for the gas. Carbon monoxide also combines with hemoglobin and myoglobin with the help of facilitated diffusion just as it is

neg: Facilitated diffusion the steady-state of diffusion of oxygen at various pressures. Oxygen-facilitated diffusion occurs in a homogeneous environment where oxygen pressure can be relatively controlled. Glucose is a six-carbon sugar that provides energy needed by cells. Since glucose is a large molecule, it is difficult to be transported across the membrane through passive diffusion Hence, it diffuses across membranes through facilitated diffusion, down the concentration gradient. The carrier protein at the membrane binds to the glucose and alters its shape such that it can easily to be transported from one side of the membrane to the other. Movement of glucose into the

neg: Membrane transport protein translocation so that the opening in the protein now faces the other side of the plasma membrane. The carrier protein substrate is released at that site, according to its binding affinity there. Facilitated diffusion is the passage of molecules or ions across a biological membrane through specific transport proteins and requires no energy input. Facilitated diffusion is used especially in the case of large polar molecules and charged ions; once such ions are dissolved in water they cannot diffuse freely across cell membranes due to the hydrophobic nature of the fatty acid tails of the phospholipids that make up the

neg: Cell membrane as a selective filter that allows only certain things to come inside or go outside the cell. The cell employs a number of transport mechanisms that involve biological membranes: 1. Passive osmosis and diffusion: Some substances (small molecules, ions) such as carbon dioxide (CO) and oxygen (O), can move across the plasma membrane by diffusion, which is a passive transport process. Because the membrane acts as a barrier for certain molecules and ions, they can occur in different concentrations on the two sides of the membrane. Diffusion occurs when small molecules and ions move freely from high concentration to low

neg: Passive transport concentration until the concentration of the solute is uniform throughout and reaches equilibrium. Osmosis is much like simple diffusion but it specifically describes the movement of water (not the solute) across a selectively permeable membrane until there is an equal concentration of water and solute on both sides of the membrane. Simple diffusion and osmosis are both forms of passive transport and require none of the cell's ATP energy. Facilitated diffusion, also called carrier-mediated osmosis, is the movement of molecules across the cell membrane via special transport proteins that are embedded in the plasma membrane by actively taking up or

neg: Facilitated diffusion in oxygen but the rate at which they react differs from one another. Carbon monoxide has a dissociation velocity which is 100 times less than that of oxygen; its affinity for myoglobin is 40 times higher and 250 times higher for hemoglobin, compared to oxygen. Facilitated diffusion Facilitated diffusion (also known as facilitated transport or passive-mediated transport) is the process of spontaneous passive transport (as opposed to active transport) of molecules or ions across a biological membrane via specific transmembrane integral proteins. Being passive, facilitated transport does not directly require chemical energy from ATP hydrolysis in the transport step itself;

neg: Leishmania major several macrophage receptors. Promastigote attachment to macrophages is facilitated by a number of receptors, including complement receptors CR1 and CR3, and the receptor for advanced glycosylation end products. Activation of complements occurs far from the cell membrane, and insertion of the membrane attack complex does not occur. This action is what allows the parasite to avoid being lysed, and to persist within the host's macrophages. The incidence rate of cutaneous leishmaniasis is estimated to be between 1-1.5 million cases a year. However, transmission does not often occur "in utero", during blood transfusions, or through interpersonal contact. Thus, the main form

neg: Surface chemistry of microvasculature are also known as Van der Waals forces, which is determined by the Keesom, Debye and London Dispersion forces. The lipid bilayer of an endothelial cell membrane is a hydrophobic surface. The non-polar lipids lead to a very high electrical resistivity, given by: formula_2 Where: This high resistivity prevents ions from crossing the bilayer without an integral membrane protein using facilitated diffusion. Drugs diffuse through capillary walls in the same manner as endogenous molecules. One of the most important examples of this is drug diffusion across the blood brain barrier. The blood brain barrier consists of a bed of continuous

neg: Proton-exchange membrane fuel cell assemblies (MEA) which include the electrodes, electrolyte, catalyst, and gas diffusion layers. An ink of catalyst, carbon, and electrode are sprayed or painted onto the solid electrolyte and carbon paper is hot pressed on either side to protect the inside of the cell and also act as electrodes. The pivotal part of the cell is the triple phase boundary (TPB) where the electrolyte, catalyst, and reactants mix and thus where the cell reactions actually occur. Importantly, the membrane must not be electrically conductive so the half reactions do not mix. Operating temperatures above 100 °C are desired so the water

neg: Cell membrane 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. Nutrients, such as sugars or amino acids, must enter the cell, and certain products of metabolism must leave the cell. Such molecules can diffuse passively through protein channels such as aquaporins in facilitated diffusion or are pumped across the membrane by transmembrane transporters. Protein channel proteins, also called "permeases", are usually quite specific, and they only recognize and transport a limited variety of chemical substances, often limited to a single

neg: Osmosis membrane (vacuole) or protoplast by diffusing across the phospholipid bilayer via aquaporins (small transmembrane proteins similar to those responsible for facilitated diffusion and ion channels). Osmosis provides the primary means by which water is transported into and out of cells. The turgor pressure of a cell is largely maintained by osmosis across the cell membrane between the cell interior and its relatively hypotonic environment. Some kinds of osmotic flow have been observed since ancient times, e.g., on the construction of Egyptian pyramids. Jean-Antoine Nollet first documented observation of osmosis in 1748. The word "osmosis" descends from the words "endosmose" and

neg: Uniporter Uniporter A uniporter is an integral membrane protein that transports a single type of substrate species (charged or uncharged) across a cell membrane. It may use either facilitated diffusion and transport along a diffusion gradient or transport against one with an active transport process.. They can be either ion channels or carrier proteins. Uniporter carrier proteins work by binding to one molecule of substrate at a time. Uniporter channels open in response to a stimulus and allow the free flow of specific molecules. There are several ways in which the opening of uniporter channels may be regulated: Uniporters are involved

neg: Cell biology pressure, diffusion, concentration gradients, and membrane channels. Inside of the cell are extensive internal sub-cellular membrane-bounded compartments called organelles. Cells contains specialized sub-cellular compartments including cell membrane, cytoplasm,mitochondria, and ribosomes. See organelle. The growth process of the cell does not refer to the size of the cell, but instead the density of the number of cells present in the organism at a given time. Cell growth pertains to the increase in the number of cells present in an organism as it grows and develops; as the organism gets larger so too does the number of cells present. Cells are the

neg: Fluid mosaic model lipid and membrane proteins can diffuse freely, but that they can seldom leave. Restriction on lateral diffusion rates of membrane components is very important because it allows the functional specialization of particular regions within the cell membranes. Lipid rafts are membrane nanometric platforms with a particular lipid and protein composition that laterally diffuse, navigating on the liquid bilipid layer. Sphingolipids and cholesterol are important building blocks of the lipid rafts. Cell membrane proteins and glycoproteins do not exist as single elements of the lipid membrane, as first proposed by Singer and Nicolson in 1972. Rather, they occur as diffusing complexes

neg: Facilitated diffusion diffusion is saturable with respect to the concentration difference between the two phases; unlike free diffusion which is linear in the concentration difference. Third, the temperature dependence of facilitated transport is substantially different due to the presence of an activated binding event, as compared to free diffusion where the dependence on temperature is mild. Polar molecules and large ions dissolved in water cannot diffuse freely across the plasma membrane due to the hydrophobic nature of the fatty acid tails of the phospholipids that make up the lipid bilayer. Only small, non-polar molecules, such as oxygen and carbon dioxide, can diffuse

neg: Permease Permease The permeases are membrane transport proteins, a class of multipass transmembrane proteins that allow the diffusion of a specific molecule in or out of the cell in the direction of a concentration gradient, a form of facilitated diffusion. The permease binding is first step of translocation. LacY protein from Escherichia coli is an example of a permease. It was originally discovered in the 1930s by Joy Adames. It is a transporter protein that helps in various aspects of cellular life including DNA replication, translation of RNA, and diffusion. A permease (porter) is a protein or protein complex that catalyzes

neg: Molecular diffusion Chemical potential) an energy flow will occur from S to S, because nature always prefers low energy and maximum entropy. Molecular diffusion is typically described mathematically using Fick's laws of diffusion. Diffusion is of fundamental importance in many disciplines of physics, chemistry, and biology. Some example applications of diffusion: Diffusion is part of the transport phenomena. Of mass transport mechanisms, molecular diffusion is known as a slower one. In cell biology, diffusion is a main form of transport for necessary materials such as amino acids within cells. Diffusion of solvents, such as water, through a semipermeable membrane is classified as

neg: Bacterial cell structure for a large surface area-to-volume ratio which allows for rapid uptake and intracellular distribution of nutrients and excretion of wastes. At low surface area-to-volume ratios the diffusion of nutrients and waste products across the bacterial cell membrane limits the rate at which microbial metabolism can occur, making the cell less evolutionarily fit. The reason for the existence of large cells is unknown, although it is speculated that the increased cell volume is used primarily for storage of excess nutrients. The cell envelope is composed of the plasma membrane and cell wall. As in other organisms, the bacterial cell wall provides

neg: Transport protein transport substances. The proteins may assist in the movement of substances by facilitated diffusion (i.e., passive transport) or active transport. These mechanisms of movement are known as carrier-mediated transport. Each carrier protein is designed to recognize only one substance or one group of very similar substances. Research has correlated defects in specific carrier proteins with specific diseases. A membrane transport protein (or simply "transporter") is a membrane protein that acts as such a carrier. A vesicular transport protein is a transmembrane or membrane associated protein. It regulates or facilitates the movement by vesicles of the contents of the cell. Transport

neg: Beta cell glucose concentration outside the cell is high, glucose molecules move into the cell by facilitated diffusion, down its concentration gradient through the GLUT2 transporter. Since beta cells use glucokinase to catalyze the first step of glycolysis, metabolism only occurs around physiological blood glucose levels and above. Metabolism of the glucose produces ATP, which increases the ATP to ADP ratio. The ATP-sensitive potassium ion channels close when this ratio rises. This means that potassium ions can no longer diffuse out of the cell. As a result, the potential difference across the membrane becomes more positive (as potassium ions accumulate inside the

neg: Membrane transport protein by the transporter. Transporter reversal typically occurs when a membrane transport protein is phosphorylated by a particular protein kinase, which is an enzyme that adds a phosphate group to proteins. Facilitated diffusion occurs in and out of the cell membrane via channels/pores and carriers/porters. Note: Channels are either in open state or closed state. When a channel is opened with a slight conformational switch, it is open to both environment simultaneously (extracellular and intracellular) Pores are continuously open to these both environment, because they do not undergo conformational changes. They are always open and active. The group translocators provide a

neg: Postsynaptic potential on the membrane of the postsynaptic cell. One way receptors can react to being bound by a neurotransmitter is to open or close an ion channel, allowing ions to enter or leave the cell. It is these ions that alter the membrane potential. Ions are subject to two main forces, diffusion and electrostatic repulsion. Ions will tend towards their equilibrium potential, which is the state where the diffusion force cancels out the force of electrostatic repulsion. When a membrane is at its equilibrium potential, there is no longer a net movement of ions. Two important equations that can determine membrane

neg: Blood sugar regulation from the blood through the GLUT4 transporter, thus decreasing blood sugar. When insulin binds to the receptors on the cell surface, vesicles containing the GLUT4 transporters come to the plasma membrane and fuse together by the process of endocytosis, thus enabling a facilitated diffusion of glucose into the cell. As soon as the glucose enters the cell, it is phosphorylated into Glucose-6-Phosphate in order to preserve the concentration gradient so glucose will continue to enter the cell. Insulin also provides signals to several other body systems, and is the chief regulator of metabolic control in humans. There are also several

neg: Permease a vectorial reaction, irrespective of whether or not it also catalyzes a chemical or electron transfer reaction that drives the vectorial process. Permease The permeases are membrane transport proteins, a class of multipass transmembrane proteins that allow the diffusion of a specific molecule in or out of the cell in the direction of a concentration gradient, a form of facilitated diffusion. The permease binding is first step of translocation. LacY protein from Escherichia coli is an example of a permease. It was originally discovered in the 1930s by Joy Adames. It is a transporter protein that helps in various aspects

neg: Cell membrane concentration in order to equilibrate the membrane. It is considered a passive transport process because it does not require energy and is propelled by the concentration gradient created by each side of the membrane. 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

neg: Cytolysis Cytolysis Cytolysis, or osmotic lysis, occurs when a cell bursts due to an osmotic imbalance that has caused excess water to diffuse into the cell. Water can enter the cell by diffusion through the cell membrane or through selective membrane channels called aquaporins, which greatly facilitate the flow of water. It occurs in a hypotonic environment, where water moves into the cell by osmosis and causes its volume to increase to the point where the volume exceeds the membrane's capacity and the cell bursts. The presence of a cell wall prevents the membrane from bursting, so cytolysis only occurs in

neg: Membrane transport protein bilayers. The type of carrier proteins used in facilitated diffusion is slightly different from those used in active transport. They are still transmembrane carrier proteins, but these are gated transmembrane channels, meaning they do not internally translocate, nor require ATP to function. The substrate is taken in one side of the gated carrier, and without using ATP the substrate is released into the cell. They may be used as potential biomarkers Reverse transport, or "transporter reversal", is a phenomenon in which the substrates of a membrane transport protein are moved in the opposite direction to that of their typical movement

neg: Semipermeable membrane types of semipermeable membranes are cation exchange membrane (CEM), charge mosaic membrane (CMM), bipolar membrane (BPM), anion exchange membrane (AEM) alkali anion exchange membrane (AAEM) and proton exchange membrane (PEM). Semipermeable membrane A semipermeable membrane is a type of biological or synthetic, polymeric membrane that will allow certain molecules or ions to pass through it by diffusion—or occasionally by more specialized processes of facilitated diffusion, passive transport or active transport. The rate of passage depends on the pressure, concentration, and temperature of the molecules or solutes on either side, as well as the permeability of the membrane to each solute.

neg: Semipermeable membrane Semipermeable membrane A semipermeable membrane is a type of biological or synthetic, polymeric membrane that will allow certain molecules or ions to pass through it by diffusion—or occasionally by more specialized processes of facilitated diffusion, passive transport or active transport. The rate of passage depends on the pressure, concentration, and temperature of the molecules or solutes on either side, as well as the permeability of the membrane to each solute. Depending on the membrane and the solute, permeability may depend on solute size, solubility, properties, or chemistry. How the membrane is constructed to be selective in its permeability will determine

neg: Membrane potential diffusion. Membrane potential The term "membrane potential" may refer to one of three kinds of membrane potential: Membrane potential (also transmembrane potential or membrane voltage) is the difference in electric potential between the interior and the exterior of a biological cell. With respect to the exterior of the cell, typical values of membrane potential, normally given in millivolts, range from –40 mV to –80 mV. All animal cells are surrounded by a membrane composed of a lipid bilayer with proteins embedded in it. The membrane serves as both an insulator and a diffusion barrier to the movement of ions. Transmembrane

neg: Facilitated diffusion it was deduced that facilitated diffusion in eukaryotes precipitates the searching process and minimizes the searching time by increasing the DNA-protein affinity. Oxygen binds with red blood cells in the blood stream. The oxygen affinity with hemoglobin on red blood cell surfaces enhances this bonding ability. In a system of facilitated diffusion of oxygen, there is a tight relationship between the ligand which is oxygen and the carrier which is either hemoglobin or myoglobin. This mechanism of facilitated diffusion of oxygen by hemoglobin or myoglobin was discovered and initiated by Wittenberg and Scholander. They carried out experiments to test for

neg: Glycogenolysis the fight-or-flight response and the regulation of glucose levels in the blood. In myocytes (muscle cells), glycogen degradation serves to provide an immediate source of glucose-6-phosphate for glycolysis, to provide energy for muscle contraction. In hepatocytes (liver cells), the main purpose of the breakdown of glycogen is for the release of glucose into the bloodstream for uptake by other cells. The phosphate group of glucose-6-phosphate is removed by the enzyme glucose-6-phosphatase, which is not present in myocytes, and the free glucose exits the cell via GLUT2 facilitated diffusion channels in the hepatocyte cell membrane. Glycogenolysis is regulated hormonally in response

neg: Facilitated diffusion main mechanism behind the binding of Transcription Factors (TFs) to designated target sites on the DNA molecule. The in vitro model, which is a very well known method of facilitated diffusion, that takes place outside of a living cell, explains the 3-dimensional pattern of diffusion in the cytosol and the 1-dimensional diffusion along the DNA contour. After carrying out extensive research on processes occurring out of the cell, this mechanism was generally accepted but there was a need to verify that this mechanism could take place in vivo or inside of living cells. Bauer & Metzler (2013) therefore carried out

neg: Membrane potential the membrane potential, while the membrane potential itself is influenced by these same ion channels, feedback loops that allow for complex temporal dynamics arise, including oscillations and regenerative events such as action potentials. The membrane potential in a cell derives ultimately from two factors: electrical force and diffusion. Electrical force arises from the mutual attraction between particles with opposite electrical charges (positive and negative) and the mutual repulsion between particles with the same type of charge (both positive or both negative). Diffusion arises from the statistical tendency of particles to redistribute from regions where they are highly concentrated to regions

neg: Membrane potential of a volt), but calculations show that this generates an electric field close to the maximum that the membrane can sustain—it has been calculated that a voltage difference much larger than 200 millivolts could cause dielectric breakdown, that is, arcing across the membrane. The resistance of a pure lipid bilayer to the passage of ions across it is very high, but structures embedded in the membrane can greatly enhance ion movement, either actively or passively, via mechanisms called facilitated transport and facilitated diffusion. The two types of structure that play the largest roles are ion channels and ion pumps, both

neg: GLUT2 GLUT2 Glucose transporter 2 (GLUT2) also known as solute carrier family 2 (facilitated glucose transporter), member 2 (SLC2A2) is a transmembrane carrier protein that enables protein facilitated glucose movement across cell membranes. It is the principal transporter for transfer of glucose between liver and blood, and has a role in renal glucose reabsorption. It is also capable of transporting fructose. Unlike GLUT4, it does not rely on insulin for facilitated diffusion. In humans, this protein is encoded by the "SLC2A2" gene. GLUT2 is found in cellular membranes of: GLUT2 has high capacity for glucose but low affinity (high K, ca.

neg: Extracellular digestion here the digestion is intracellular. Extracellular digestion Extracellular 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, 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. The prefix "extra" means "outside", and indicates that extracellular digestion must occur outside the cell. During

neg: Extracellular digestion Extracellular digestion Extracellular 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, 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. The prefix "extra" means "outside", and indicates that extracellular digestion must occur outside the cell. During extracellular digestion, food is broken

neg: Cell junction diffusion without contact with the extracellular fluid. This is possible due to six connexin proteins interacting to form a cylinder with a pore in the centre called a connexon. The connexon complexes stretches across the cell membrane and when two adjacent cell connexons interact, they form a complete gap junction channel. Connexon pores vary in size, polarity and therefore can be specific depending on the connexin proteins that constitute each individual connexon. Whilst variation in gap junction channels do occur, their structure remains relatively standard, and this interaction ensures efficient communication without the escape of molecules or ions to the

neg: Biological membrane succeed in doing so. Selective permeability is essential for effective separation of a cell or organelle from its surroundings. Biological membranes also have certain mechanical or elastic properties that allow them to change shape and move as required. Generally, small hydrophobic molecules can readily cross phospholipid bilayers by simple diffusion. Particles that are required for cellular function but are unable to diffuse freely across a membrane enter through a membrane transport protein or are taken in by means of endocytosis, where the membrane allows for a vacuole to join onto it and push its contents into the cell. Many types

neg: Mitosis interphase nuclei. During mitotic progression, typically after the anaphase onset, the cell may undergo cytokinesis. In animal cells, a cell membrane pinches inward between the two developing nuclei to produce two new cells. In plant cells, a cell plate forms between the two nuclei. Cytokinesis does not always occur; coenocytic (a type of multinucleate condition) cells undergo mitosis without cytokinesis. The mitotic phase is a relatively short period of the cell cycle. It alternates with the much longer "interphase", where the cell prepares itself for the process of cell division. Interphase is divided into three phases: G (first gap), S

neg: GLUT4 of either exercise or muscle contraction. During exercise, the body needs to convert glucose to ATP to be used as energy. As G-6-P concentrations decrease, hexokinase becomes less inhibited, and the glycolytic and oxidative pathways that make ATP are able to proceed. This also means that muscle cells are able to take in more glucose as its intracellular concentrations decrease. In order to increase glucose levels in the cell, GLUT4 is the primary transporter used in this facilitated diffusion. Although muscle contractions function in a similar way and also induce the translocation of GLUT4 into the plasma membrane, the two

neg: Ion transporter equilibrium the concentrations of the ion in both areas will be equal, so if there is a difference in concentration the ions will seek to flow "down" the concentration gradient or from a high concentration to low concentration. Ion channels allows the specific ions that will fit into the channel to flow down their concentration gradient, equalizing the concentrations on either side of the cell membrane. Ion channels accomplish this via facilitated diffusion which is a type of passive transport. In contrast, ion transporters perform active transport by moving ions against their concentration gradient. Using energy sources such as ATP,

neg: Membrane fluidity Consequently, membrane-dependent functions, such as phagocytosis and cell signalling, can be regulated by the fluidity of the cell-membrane. Membrane fluidity In biology, membrane fluidity refers to the viscosity of the lipid bilayer of a cell membrane or a synthetic lipid membrane. Lipid packing can influence the fluidity of the membrane. Viscosity of the membrane can affect the rotation and diffusion of proteins and other bio-molecules within the membrane, there-by affecting the functions of these things. Membrane fluidity can be affected by a number of factors. One way to increase membrane fluidity is to heat up the membrane. Lipids acquire thermal

neg: Cell encapsulation Cell encapsulation Cell microencapsulation technology involves immobilization of the cells within a polymeric semi-permeable membrane that permits the bidirectional diffusion of molecules such as the influx of oxygen, nutrients, growth factors etc. essential for cell metabolism and the outward diffusion of waste products and therapeutic proteins. At the same time, the semi-permeable nature of the membrane prevents immune cells and antibodies from destroying the encapsulated cells regarding them as foreign invaders. The main motive of cell encapsulation technology is to overcome the existing problem of graft rejection in tissue engineering applications and thus reduce the need for long-term use of

neg: DiI similar to tetramethyl rhodamine. It is mildly fluorescent in aqueous suspension, but becomes bright when bound to cell membrane. Once bound to a membrane it diffuses laterally in 2 dimensions; if there is no diffusion barrier, DiI generally stains the whole leaflet (one surface) of a biological membrane rapidly, but does not readily flip across to the other leaflet. DiI DiI, pronounced like Dye Aye, also known as DiIC(3), is a fluorescent lipophilic cationic indocarbocyanine dye which is usually made as a perchlorate salt. It is used for scientific staining purposes such as single molecule imaging, fate mapping, electrode marking

neg: GJB1 consist of six connexin molecules (gap junction trans-membrane proteins)., This enables communication between Schwann cell nuclei and axons through a radial diffusion pathway. GJB1 functions as a radial diffusion pathway, allowing the communication and diffusion of nutrients, ions and small molecules between cells. The GJB1 protein is found in a number of organs, including the liver, kidney, pancreas and nervous system. In normal circumstances this protein is located in the cell membrane of Schwann cells and oligodendrocytes, specialised cells of the nervous system., These cells typically encapsulate nerves that are involved in the assembly and preservation of myelin, to ensure

neg: Homeoviscous adaptation Homeoviscous adaptation Homeoviscous adaptation is the adaptation of the cell membrane lipid composition to keep the adequate membrane fluidity. The maintenance of proper cell membrane fluidity is of critical importance for the function and integrity of the cell, essential for the mobility and function of embedded proteins and lipids, diffusion of proteins and other molecules laterally across the membrane for signaling reactions, and proper separation of membranes during cell division. A fundamental biophysical determinant of membrane fluidity is the balance between saturated and unsaturated fatty acids. Regulating membrane fluidity is especially important in poikilothermic organisms such as bacteria, fungi, protists,

neg: Membrane technology membranes are increasingly used, for example in fuel cells and in osmotic power plants. Two basic models can be distinguished for mass transfer through the membrane: In real membranes, these two transport mechanisms certainly occur side by side, especially during ultra-filtration. In the solution-diffusion model, transport occurs only by diffusion. The component that needs to be transported must first be dissolved in the membrane. The general approach of the solution-diffusion model is to assume that the chemical potential of the feed and permeate fluids are in equilibrium with the adjacent membrane surfaces such that appropriate expressions for the chemical potential

neg: Cell encapsulation Anemia, and HGH for Dwarfism. In addition, monogeneic diseases such as haemophilia, Gaucher's disease and some Mucopolysaccharide disorders could also potentially be targeted by encapsulated cells expressing the protein that is otherwise lacking in the patient. Cell encapsulation Cell microencapsulation technology involves immobilization of the cells within a polymeric semi-permeable membrane that permits the bidirectional diffusion of molecules such as the influx of oxygen, nutrients, growth factors etc. essential for cell metabolism and the outward diffusion of waste products and therapeutic proteins. At the same time, the semi-permeable nature of the membrane prevents immune cells and antibodies from destroying the

neg: Membrane transport that is, by metabolic energy, or as channels of facilitated diffusion. A physiological process can only take place if it complies with basic thermodynamic principles. Membrane transport obeys physical laws that define its capabilities and therefore its biological utility. A general principle of thermodynamics that governs the transfer of substances through membranes and other surfaces is that the exchange of free energy, Δ"G", for the transport of a mole of a substance of concentration C in a compartment to another compartment where it is present at C is: Where C is less than C Δ"G" is negative, and the process

neg: Cell membrane proteins must be inserted in some way into the membrane. For this to occur, an N-terminus "signal sequence" of amino acids directs proteins to the endoplasmic reticulum, which inserts the proteins into a lipid bilayer. Once inserted, the proteins are then transported to their final destination in vesicles, where the vesicle fuses with the target membrane. The cell membrane surrounds the cytoplasm of living cells, physically separating the intracellular components from the extracellular environment. The cell membrane also plays a role in anchoring the cytoskeleton to provide shape to the cell, and in attaching to the extracellular matrix and other

neg: Microtubule microtubules, and thus the entire Centrosome towards the cell membrane. As stated above, this helps the Centrosomes orient themselves away from each other in the cell. However these astral microtubules do not interact with the mitotic spindle itself. Experiments have shown that without these astral microtubules, the mitotic spindle can form, however it orientation in the cell is not always correct and thus mitosis does not occur as effectively. Another key function of the astral microtubules is to aid in cytokinesis. Astral microtubules interact with motor proteins at the cell membrane to pull the spindle and the entire cell apart

neg: GLUT1 which glucose can traverse, with the hydrophobic regions on the outside of the channel adjacent to the fatty acid tails of the membrane. Energy-yielding metabolism in erythrocytes depends on a constant supply of glucose from the blood plasma, where the glucose concentration is maintained at about 5mM. Glucose enters the erythrocyte by facilitated diffusion via a specific glucose transporter, at a rate about 50,000 times greater than uncatalyzed transmembrane diffusion. The glucose transporter of erythrocytes (called GLUT1 to distinguish it from related glucose transporters in other tissues) is a type III integral protein with 12 hydrophobic segments, each of which

neg: Cell membrane distinct types of cells and may have therefore specific names for certain cell types. 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 the molar mass of the molecule. Due to the cell membrane's hydrophobic nature, small electrically neutral molecules pass through the membrane more easily than charged, large ones. The inability of charged molecules to pass through the cell membrane results in pH partition of substances throughout the

neg: Biological neuron model membrane potential, reflecting the diffusion of ions that occurs through the membrane when some equilibrium is not reached in the cell. The model looks like where is the membrane resistance, as we find it is not a perfect insulator as assumed previously. This forces the input current to exceed some threshold in order to cause the cell to fire, else it will simply leak out any change in potential. The firing frequency thus looks like which converges for large input currents to the previous leak-free model with refractory period. Recent advances in computational and theoretical fractional calculus lead to a

neg: Rous sarcoma virus the host cell. There are two ways viruses can enter the host cell: cell receptor endocytosis or fusion. Endocytosis is the process where the virus binds a receptor on the target cell membrane, and the virus is taken into or endocytosed into the cell. Endocytosis can either be pH independent or pH dependent. Fusion occurs when the virus fuses together with the target cell membrane and releases its genome into the cell. RSV enters the host cell through fusion of the host cell membrane. In order for the RSV genome transcription to occur, a primer is required. 4S RNA is

neg: Cytorrhysis equal to the external atmospheric pressure, has been reached, generating negative pressure within the cell. That negative pressure pulls the center of the cell inward until the cell wall can no longer withstand the strain. The inward pressure causes the majority of the collapse to occur in the central region of the cell, pushing the organelles within the remaining cytoplasm against the cell walls. Unlike in plasmolysis (a phenomenon that does not occur in nature), the plasma membrane maintains its connections with the cell wall both during and after cellular collapse. Cytorrhysis of plant cells can be induced in laboratory

neg: Endomembrane system that perform the functions of the plasma membrane. The plasma membrane is not a fixed or rigid structure, the molecules that compose the membrane are capable of lateral movement. This movement and the multiple components of the membrane are why it is referred to as a fluid mosaic. Smaller molecules such as carbon dioxide, water, and oxygen can pass through the plasma membrane freely by diffusion or osmosis. Larger molecules needed by the cell are assisted by proteins through active transport. The plasma membrane of a cell has multiple functions. These include transporting nutrients into the cell, allowing waste to

neg: Kinetic-segregation model of T cell activation stimulating tyrosine phosphorylation. In the resting T-cell, the molecules involved in this process are repeatedly colliding by means of diffusion. The TCR/CD3 complex is constantly being phosphorylated by Lck (membrane associated tyrosine kinase) and in turn continuously dephosphorylated by CD45 (tyrosine phosphatase). It all happens in a random manner and as a result the overall phosphorylation of TCR is low. T-cell activation does not proceed. The TCR/peptide-MHC complex, formed when a T-cell recognizes its ligand and the T-cell-APC contact occurs, spans a short length. As the authors propose, this forms small zones of close contact, from which the inhibitory CD45

neg: Membrane transport protein Membrane transport protein A membrane transport protein (or simply transporter) is a membrane protein involved in the movement of ions, small molecules, or macromolecules, such as another protein, across a biological membrane. Transport proteins are integral transmembrane proteins; that is they exist permanently within and span the membrane across which they transport substances. The proteins may assist in the movement of substances by facilitated diffusion or active transport. The two main types of proteins involved in such transport are broadly categorized as either "channels" or "carriers". The solute carriers and atypical SLCs are secondary active or facilitative transporters in humans.

neg: Homeoviscous adaptation plants, fish and other ectothermic animals. The general trend is an increase in unsaturated fatty acids at lower growth temperatures and an increase in saturated fatty acids at higher temperatures. Homeoviscous adaptation Homeoviscous adaptation is the adaptation of the cell membrane lipid composition to keep the adequate membrane fluidity. The maintenance of proper cell membrane fluidity is of critical importance for the function and integrity of the cell, essential for the mobility and function of embedded proteins and lipids, diffusion of proteins and other molecules laterally across the membrane for signaling reactions, and proper separation of membranes during cell division.

neg: Membrane potential Membrane potential The term "membrane potential" may refer to one of three kinds of membrane potential: Membrane potential (also transmembrane potential or membrane voltage) is the difference in electric potential between the interior and the exterior of a biological cell. With respect to the exterior of the cell, typical values of membrane potential, normally given in millivolts, range from –40 mV to –80 mV. All animal cells are surrounded by a membrane composed of a lipid bilayer with proteins embedded in it. The membrane serves as both an insulator and a diffusion barrier to the movement of ions. Transmembrane proteins,

neg: Cerebral edema include physical disruption by arterial hypertension or trauma, and tumor-facilitated release of vasoactive and endothelial destructive compounds (e.g. arachidonic acid, excitatory neurotransmitters, eicosanoids, bradykinin, histamine, and free radicals). Subtypes of vasogenic edema include: In cytotoxic edema, the blood–brain barrier remains intact but a disruption in cellular metabolism impairs functioning of the sodium and potassium pump in the glial cell membrane, leading to cellular retention of sodium and water. Swollen astrocytes occur in gray and white matter. Cytotoxic edema is seen with various toxins, including dinitrophenol, triethyltin, hexachlorophene, and isoniazid. It can occur in Reye's syndrome, severe hypothermia, early ischemia, encephalopathy,

neg: Fluid mosaic model Fluid mosaic model The fluid mosaic model explains various observations regarding the structure of functional cell membranes. According to this model, there is a lipid bilayer in which the protein molecules are embedded. The lipid bilayer gives fluidity and elasticity to the membrane. Small amounts of carbohydrates are also found in cell membrane. The model, which was devised by SJ Singer and GL Nicolson in 1972, describes the cell membrane as a two-dimensional liquid that restricts the lateral diffusion of membrane components. Such domains are defined by the existence of regions within the membrane with special lipid and protein composition

neg: Maltoporin Maltoporin Maltoporins (or LamB porins) are a family of outer membrane proteins. Maltoporin forms a trimeric structure which facilitates the diffusion of maltodextrins across the outer membrane of Gram-negative bacteria. The membrane channel is formed by an antiparallel beta-barrel. Maltoporin is a trimeric channel on the bacterial outer membrane. Most pores used for diffusion contain only 16 antiparallel strands, but Maltoporin has 18. The structure of Maltoporin contains long loops and short turns. The long loops are in contact with the cell exterior and the turns are in contact with the periplasm. This channel is involved in sugar transport. The

neg: Ohmic heating (food processing) method. Microbial inactivation in ohmic heating is achieved by both thermal and non-thermal cellular damage from the electrical field. This method destroys microorganisms due to electroporation of cell membranes, membrane rupture, and cell lysis. In electroporation, excessive leakage of ions and intramolecular components results in cell death. In membrane rupture, cells swell due to an increase in moisture diffusion across the cell membrane. Pronounced disruption and decomposition of cell walls and cytoplasmic membranes causes cells to lyse. Decreased processing times in ohmic heating maintains nutritional and sensory properties of foods. Ohmic heating inactivates antinutritional factors like lipoxigenase (LOX), polyphenoloxidase (PPO),

neg: Tonicity water across the cell membrane. Water molecules freely diffuse through the plasma membrane in both directions, and as the rate of water diffusion is the same in each direction, the cell will neither gain nor lose water. An iso-osmolar solution can be hypotonic if the solute is able to penetrate the cell membrane. For example, an iso-osmolar urea solution is hypotonic to red blood cells, causing their lysis. This is due to urea entering the cell down its concentration gradient, followed by water. The osmolarity of normal saline, 9 grams NaCl dissolved in water to a total volume of one

neg: Protonophore by passive diffusion and simultaneously facilitate proton transport. Protonophores uncouple oxidative phosphorylation via a decrease in the membrane potential of the inner membrane of mitochondria. They stimulate mitochondria respiration and heat production. Protonophores (uncouplers) are often used in biochemistry research to help explore the bioenergetics of chemiosmotic and other membrane transport processes. It has been reported that the protonophore has antibacterial activity by perturbing bacterial proton motive force . Representative protonophores include: The facilitated transport of protons across the biological membrane by protonophore is achieved as follows. Protonophore A protonophore, also known as a proton translocator, is an ionophore that

neg: Suction pressure pressure decreases. The difference between diffusion pressure of pure water and solution is called diffusion pressure deficit (DPD). When a plant cell is placed in hypotonic solution, water enters into a cell by osmosis and as a result turger pressure develops. The cell membrane get stretched and osmotic pressure of cell decreases. As cell absorbs more and more water its Total Pressure increases and Osmotic Pressure decreases. When a cell is fully turgid, its OP is equal to TP and DPD is zero. Turgid cells cannot absorb any more water. Thus, with reference to plant cell, the DPD can be

neg: Microbial fuel cell applications. The sub-category of phototrophic MFCs that use purely oxygenic photosynthetic material at the anode are sometimes called biological photovoltaic systems. 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. MFCs that do not

neg: Tonicity pushes the cell membrane against the cell wall. Due to the rigidity of the cell wall, it pushes back, preventing the cell from bursting. This is called turgor pressure. A solution is isotonic when its effective osmole concentration is the same as that of another solution. In biology, the solutions on either side of a cell membrane are isotonic if the concentration of solutes outside the cell is equal to the concentration of solutes inside the cell. In this case the cell neither swells nor shrinks because there is no concentration gradient to induce the diffusion of large amounts of

neg: Nernst equation of the ion both inside and outside the cell: When the membrane is in thermodynamic equilibrium (i.e., no net flux of ions), the membrane potential must be equal to the Nernst potential. However, in physiology, due to active ion pumps, the inside and outside of a cell are not in equilibrium. In this case, the resting potential can be determined from the Goldman equation, which is a solution of G-H-K influx equation under the constraints that total current density driven by electrochemical force is zero : The potential across the cell membrane that exactly opposes net diffusion of a particular

neg: Action potential Hodgkin–Huxley membrane capacitance model, the speed of transmission of an action potential was undefined and it was assumed that adjacent areas became depolarised due to released ion interference with neighbouring channels. Measurements of ion diffusion and radii have since shown this not to be possible. Moreover, contradictory measurements of entropy changes and timing disputed the capacitance model as acting alone. Nearly all cell membranes in animals, plants and fungi maintain a voltage difference between the exterior and interior of the cell, called the membrane potential. A typical voltage across an animal cell membrane is −70 mV. This means that the

neg: Surface chemistry of microvasculature of small molecules. Larger molecules and blood cells require adequate space between cells or holes in the lining. The high resistivity of a cellular membrane prevents the diffusion of ions without a membrane transport protein. The hydrophobicity of an endothelial cell surface determines whether water or lipophilic molecules will diffuse through the capillary lining. The blood brain barrier restricts diffusion to small hydrophobic molecules, making drug diffusion difficult to achieve. Blood flow is directly influenced by the thermodynamics of the body. Changes in temperature affect the viscosity and surface tension of the blood, altering the minimum blood flow rate. At

neg: Cell membrane 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. Flippases and scramblases concentrate phosphatidyl serine, which carries a negative charge, on the inner membrane. Along with NANA, this creates an extra barrier to charged moieties moving through the membrane. Membranes serve diverse functions in eukaryotic and prokaryotic cells. One important role is to regulate the movement of materials into and out of cells. The phospholipid bilayer structure (fluid mosaic

neg: Glucose transporter in fasting conditions, other tissues such as the intestines, muscles, brain, and kidneys are able to produce glucose following activation of gluconeogenesis. In "Saccharomyces cerevisiae" glucose transport takes place through facilitated diffusion. The transport proteins are mainly from the Hxt family, but many other transporters have been identified. GLUTs are integral membrane proteins that contain 12 membrane-spanning helices with both the amino and carboxyl termini exposed on the cytoplasmic side of the plasma membrane. GLUT proteins transport glucose and related hexoses according to a model of alternate conformation, which predicts that the transporter exposes a single substrate binding site toward

neg: Electrosynthesis in the reactor), stainless steel or reticulated vitreous carbon. Some reactions use a sacrificial electrode thatis consumed during the reaction like zinc or lead. Cell designs can be undivided cell or divided cell type. In divided cells the cathode and anode chambers are separated with a semiporous membrane. Common membrane materials include sintered glass, porous porcelain, polytetrafluoroethene or polypropylene. The purpose of the divided cell is to permit the diffusion of ions while restricting the flow of the products and reactants. This separation simplifies workup. An example of a reaction requiring a divided cell is the reduction of nitrobenzene to

neg: Insulin signal transduction pathway region called Islets of Langerhans. In the islets of Langerhans, there are beta-cells, which are responsible for production and storage of insulin. Insulin is secreted as a response mechanism for counteracting the increasing excess amounts of glucose in the blood. Glucose in the body increases after food consumption. This is primarily due to carbohydrate intake, but to a much lesser degree protein intake ()(). Depending on the tissue type, the glucose enters the cell through facilitated or passive diffusion. In muscle and adipose tissue, glucose enters through GLUT 4 receptors via facilitated diffusion (). In brain, kidney and retina, glucose

neg: Complement membrane attack complex a common MACPF domain. This region is homologous to cholesterol-dependent cytolysins from Gram-positive bacteria. The ring structure formed by C9 is a pore in the membrane that allows free diffusion of molecules in and out of the cell. If enough pores form, the cell is no longer able to survive. If the pre-MAC complexes of C5b-7, C5b-8 or C5b-9 do not insert into a membrane, they can form inactive complexes with Protein S (sC5b-7, sC5b-8 and sC5b-9). These fluid phase complexes do not bind to cell membranes and are ultimately scavenged by clusterin and vitronectin, two regulators of complement. The

neg: John A. Quinn include analysis of electrodynamic/electrokinetic effects of various microsolutes, macromolecules, and colloids as they diffused across and/or adsorbed to the walls of neutral and electrically charged membrane pores. Diffusion in reactive media and biological systems: John Quinn’s fascination with biological membrane structure and function led naturally and directly to attempts to understand and utilize biomembrane phenomena in synthetic membrane constructs – e.g., in facilitated transport membranes with potential for the industrial-scale separations of reactive gases like CO. In experiments done in collaboration with investigators at Penn’s School of Medicine, synthetic membranes were used to understand gas transport in and across the

neg: Bacterial cell structure Type IV pili (non-sex pili) also aid bacteria in gripping surfaces. An S-layer (surface layer) is a cell surface protein layer found in many different bacteria and in some archaea, where it serves as the cell wall. All S-layers are made up of a two-dimensional array of proteins and have a crystalline appearance, the symmetry of which differs between species. The exact function of S-layers is unknown, but it has been suggested that they act as a partial permeability barrier for large substrates. For example, an S-layer could conceivably keep extracellular proteins near the cell membrane by preventing their diffusion

neg: Corneal endothelium which renders it optimally transparent, the nutrition of the corneal epithelium, stromal keratocytes, and corneal endothelium must occur via diffusion of glucose and other solutes from the aqueous humor, across the corneal endothelium. The corneal endothelium then transports water from the stromal-facing surface to the aqueous-facing surface by an interrelated series of active and passive ion exchangers. Critical to this energy-driven process is the role of Na/KATPase and carbonic anhydrase. Bicarbonate ions formed by the action of carbonic anhydrase are translocated across the cell membrane, allowing water to passively follow. Corneal endothelial cells are post-mitotic and divide rarely, if at

neg: Membrane fluidity Membrane fluidity In biology, membrane fluidity refers to the viscosity of the lipid bilayer of a cell membrane or a synthetic lipid membrane. Lipid packing can influence the fluidity of the membrane. Viscosity of the membrane can affect the rotation and diffusion of proteins and other bio-molecules within the membrane, there-by affecting the functions of these things. Membrane fluidity can be affected by a number of factors. One way to increase membrane fluidity is to heat up the membrane. Lipids acquire thermal energy when they are heated up; energetic lipids move around more, arranging and rearranging randomly, making the membrane

neg: Osmotic dehydration Osmotic dehydration Osmotic dehydration is an operation used for the partial removal of water from plant tissues by immersion in a hyper-tonic (osmotic) solution. Water removal anuska is based on the natural and non-destructive phenomenon of osmosis across cell membranes. The driving force for the diffusion of water from the tissue into the solution is provided by the higher osmotic pressure of the hyper-tonic solution. The diffusion of water is accompanied by the simultaneous counter diffusion of solutes from the osmotic solution into the tissue. Since the cell membrane responsible for osmotic transport is not perfectly selective, solutes present in

neg: Ultrapure water Dissolved oxygen is measured by two basic technologies: electrochemical cell or optical fluorescence. Traditional electrochemical measurement uses a sensor with a gas-permeable membrane. Behind the membrane, electrodes immersed in an electrolyte develop an electric current directly proportional to the oxygen partial pressure of the sample. The signal is temperature compensated for the oxygen solubility in water, the electrochemical cell output and the diffusion rate of oxygen through the membrane. Optical fluorescent DO sensors use a light source, a fluorophore and an optical detector. The fluorophore is immersed in the sample. Light is directed at the fluorophore which absorbs energy and

neg: Membrane fluidity (DMPG), can take place over a wide range of temperature. Within this range of temperatures, these membranes become very viscous. Microorganisms subjected to thermal stress are known to alter the lipid composition of their cell membrane (see homeoviscous adaptation). This is one way they can adjust the fluidity of their membrane in response to their environment. Membrane fluidity is known to affect the function of biomolecules residing within or associated with the membrane structure. For example, the binding of some peripheral proteins is dependent on membrane fluidity. Lateral diffusion (within the membrane matrix) of membrane-related enzymes can affect reaction rates.

neg: GLUT1 GLUT1 Glucose transporter 1 (or GLUT1), also known as solute carrier family 2, facilitated glucose transporter member 1 (SLC2A1), is a uniporter protein that in humans is encoded by the "SLC2A1" gene. GLUT1 facilitates the transport of glucose across the plasma membranes of mammalian cells. This gene encodes a major glucose transporter in the mammalian blood-brain barrier. The encoded protein is found primarily in the cell membrane and on the cell surface, where it can also function as a receptor for human T-cell leukemia virus (HTLV) I and II. Mutations in this gene can cause GLUT1 deficiency syndrome 1, GLUT1

neg: Bacteria channels to enable better diffusion of nutrients. In natural environments, such as soil or the surfaces of plants, the majority of bacteria are bound to surfaces in biofilms. Biofilms are also important in medicine, as these structures are often present during chronic bacterial infections or in infections of implanted medical devices, and bacteria protected within biofilms are much harder to kill than individual isolated bacteria. The bacterial cell is surrounded by a cell membrane which is made primarily of phospholipids. This membrane encloses the contents of the cell and acts as a barrier to hold nutrients, proteins and other essential

neg: Juxtacrine signalling Juxtacrine signalling In biology, juxtacrine signalling (or contact-dependent signalling) is a type of cell / cell or cell / extracellular matrix signalling in multicellular organisms that requires close contact. Hence, this stands in contrast to releasing a signaling molecule by diffusion into extracellular space, or the use of long-range conduits like membrane nanotubes and cytonemes (akin to 'bridges'), or the use of extracellular vesicles like exosomes or microvesicles (akin to 'boats'). There are three types of juxtacrine signaling: Additionally, in unicellular organisms such as bacteria, juxtacrine signaling refers to interactions by membrane contact. The term "juxtacrine" was originally introduced by

neg: Cell damage of the cell that are targets of cell damage are the DNA and the cell membrane. Some cell damage can be reversed once the stress is removed or if compensatory cellular changes occur. Full function may return to cells but in some cases a degree of injury will remain. Cellular swelling (or cloudy swelling) may occur due to cellular hypoxia, which damages the sodium-potassium membrane pump; it is reversible when the cause is eliminated. Cellular swelling is the first manifestation of almost all forms of injury to cells. When it affects many cells in an organ, it causes some pallor,

neg: Cell membrane membranes by altering lipid composition is called homeoviscous adaptation. The entire membrane is held together via non-covalent interaction of hydrophobic tails, however the structure is quite fluid and not fixed rigidly in place. Under physiological conditions phospholipid molecules in the cell membrane are in the liquid crystalline state. It means the lipid molecules are free to diffuse and exhibit rapid lateral diffusion along the layer in which they are present. However, the exchange of phospholipid molecules between intracellular and extracellular leaflets of the bilayer is a very slow process. Lipid rafts and caveolae are examples of cholesterol-enriched microdomains in the

neg: Bacterial outer membrane vesicles is "bulging" of outer membrane above the peptidoglycan layer. It has been suggested (links) that few supramolecular proteins may 'rivet' the outer and cell membranes together, so that the periplasmic bulge protrudes like a 'ballooned' pocket of inflated periplasm. Lateral diffusion of 'rivet complexes' may help in pinching off large bulges of periplasm as OMVs. Detailed experimental work is still awaited to understand the biomechanics of OMV biogenesis. OMVs are also under focus of current research in exocytosis in prokaryotes via outer membrane vesicle trafficking for intra-species, inter-species and inter-kingdom cell signaling, which is slated to change our mindset on

neg: Thiomargarita namibiensis and thus capable of respiring with oxygen if it is plentiful. Gigantism is usually a disadvantage for bacteria. Bacteria obtain their nutrients via simple diffusion process across their cell membrane, as they lack the sophisticated nutrient uptake mechanism found in eukaryotes. A bacterium of large size would imply a lower ratio of cell membrane surface area to cell volume. This would limit the rate of uptake of nutrients to threshold levels. Large bacteria might starve easily unless they have a different backup mechanism. "T. namibiensis" overcomes this problem by harboring large vacuoles that can be filled up with life-supporting nitrates.

neg: Enterobacter virus CC31 for viral genomic replication to occur, "CC31" needs to enter the host, "Escherichia" "coli". Due to the lack of an outer envelope, the virion must find an alternate way to enter its host. It does this by penetrating the membrane of the bacterium with its tail region. First, the long tail fibers ejecting from the top of the base plate attach to the cell membrane of the bacterium. The small tail fibers underneath base plate then attach to the membrane, initiating a conformational change of the base plate to a six-point star from the previous hexagon conformation. This forces the