Concentration gradient on the surface layer. Sodium (Na) concentration gradient as a driving force for membrane transport
1. Effect of the Na/K pump (sodium potassium pump) on membrane potential and cell volume. Constant cell volume.
3. Endocytosis. Exocytosis.
4. Diffusion in the transport of substances within the cell. The importance of diffusion in endocytosis and exocytosis.
5. Active transport in organelle membranes.
6. Transport in cell vesicles.
7. Transport through the formation and destruction of organelles. Microfilaments.
8. Microtubules. Active movements of the cytoskeleton.
9. Axon transport. Fast axon transport. Slow axon transport.
10. Regulation of cellular functions. Regulatory effects on the cell membrane. Membrane potential.
11. Extracellular regulatory substances. Synaptic mediators. Local chemical agents (histamine, growth factor, hormones, antigens).
12. Intracellular communication with the participation of second messengers. Calcium.
13. Cyclic adenosine monophosphate, cAMP. cAMP in the regulation of cell function.
14. Inositol phosphate "IF3". Inositol triphosphate. Diacylglycerol.
Meaning Na/K pump for cell is not limited to stabilizing normal K+ and Na+ gradients across the membrane. The energy stored in the membrane Na+ gradient is often used to facilitate membrane transport of other substances. For example, in Fig. Figure 1.10 shows the “symport” of Na+ and a sugar molecule into the cell. Membrane transport protein transports a sugar molecule into the cell even against a concentration gradient, at the same time Na+ moves along concentration and potential gradients, providing energy for the transport of sugars. Such transport of Sakharov completely depends on the existence high sodium gradient I; if the intracellular sodium concentration increases significantly, the transport of sugars stops.
Rice. 1.8. The relationship between the rate of transport of molecules and their concentration (at the entrance to the channel or at the binding site of the pump) during diffusion through the channel or during pumping transport. The latter becomes saturated at high concentrations (maximum speed, V max); the value on the x-axis corresponding to half the maximum pump speed (Vmax/2) is the equilibrium concentration of KtThere are different symport systems for different sugars. Amino acid transport into the cell is similar to the transport of sugars shown in Fig. 1.10; it is also provided by the Na+ gradient; There are at least five different symport systems, each specialized for one group of related amino acids.
Rice. 1.10. Proteins immersed in the lipid bilayer of the membrane mediate the symport of glucose and Na into the cell, as well as the Ca/Na antiport, in which the driving force is the Na gradient on the cell membrane
Besides simport systems there are also " anti-porters" One of them, for example, transfers one calcium ion out of the cell in one cycle in exchange for three incoming sodium ions (Fig. 1.10). The energy for Ca2+ transport is generated by the entry of three sodium ions along the concentration and potential gradient. This energy is sufficient (at resting potential) to maintain a high calcium ion gradient (from less than 10 -7 mol/L inside the cell to approximately 2 mmol/L outside the cell).
Characterizing the magnitude and direction of the greatest change concentrations any substance in the environment. For example, if we consider two areas with different concentrations of a substance, separated by a semi-permeable membrane, then the concentration gradient will be directed from the area of lower concentration of the substance to the area with higher concentration Lua error: callParserFunction: function "#property" was not found. )]][[K:Wikipedia:Articles without sources (country: Lua error: callParserFunction: function "#property" was not found. )]] .
Definition
The concentration gradient is directed along the path l, corresponding normals to the isoconcentration surface (semipermeable membrane). Concentration gradient value texvc not found; See math/README - help with setup.): \nabla C equal to the ratio of the elementary change in concentration dC to the elementary path length dl :
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At a constant concentration gradient C along the way l :
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Here C 1 And C 2- initial and final concentration value along the path length l(normal to the isoconcentration surface).
Concentration gradients may be responsible for the transport of substances, e.g. diffusion. Diffusion occurs against the concentration gradient vector [[K:Wikipedia:Articles without sources (country: Lua error: callParserFunction: function "#property" was not found. )]][[K:Wikipedia:Articles without sources (country: Lua error: callParserFunction: function "#property" was not found. )]][[K:Wikipedia:Articles without sources (country: Lua error: callParserFunction: function "#property" was not found. )]] .
The unit of measurement for concentration gradient is International System of Units (SI) is the value −4 (mol/m 4 or kg/m 4), as well as its fractional or multiple derivatives.
see also
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Literature
- Antonov V.F., Chernysh A.M., Pasechnik V.I. Biophysics - M.: VLADOS, 2000, p. 35. ISBN 5-691-00338-0
- Trifonov E. V.- St. Petersburg: 2011.
An excerpt characterizing the Concentration Gradient
– These are Witches and Sorcerers, Isidora. Your father was once one of them... We train them.My heart ached... I wanted to howl in a wolf’s voice, feeling sorry for myself and my short lost life!.. Throwing everything away, sit down with them, with these happy Sorcerers and Witches, in order to know with my mind and heart the whole depth of the wonderful, so generously revealed to them great KNOWLEDGE! Burning tears were ready to flow like a river, but I tried with my last strength to somehow hold them back. There was no way to do this, since tears were another “forbidden luxury” to which I had no right if I considered myself a real Warrior. The soldiers did not cry. They fought and won, and if they died, it certainly wasn’t with tears in their eyes... Apparently, I was just very tired. From loneliness and pain... From constant fear for my family... From an endless struggle in which I did not have the slightest hope of emerging victorious. I really needed a breath of fresh air, and that air for me was my daughter, Anna. But for some reason, she was nowhere to be seen, although I knew that Anna was here, with them, on this wonderful and strange, “closed” land.
Sever stood next to me on the edge of the gorge, and deep sadness lurked in his gray eyes. I wanted to ask him - will I ever see him? But there was not enough strength. I didn't want to say goodbye. I didn't want to leave. Life here was so wise and calm, and everything seemed so simple and good!.. But there, in my cruel and imperfect world, good people were dying, and it was time to return to try to save at least someone... This is for real was my world, no matter how scary it was. And my father, who remained there, perhaps suffered cruelly, unable to escape from the clutches of Caraffa, whom I firmly decided, no matter what the cost, to destroy, even if for this I had to give up my short and so dear to me life...
– Can I see Anna? – I asked Sever with hope in my soul.
– Forgive me, Isidora, Anna is undergoing “cleansing” from the bustle of the world... Before she enters the same hall where you were just now. She won't be able to come to you now...
– But why didn’t I need to “clean” anything? – I was surprised. – Anna is still a child, she doesn’t have too much worldly “dirt”, does she?
GRADIENT(lat. gradiens, gradient walking) - a vector quantity showing the direction of the fastest change of any function. The concept of g. is widely used in physics, physics. chemistry, meteorology and other sciences to characterize the rate of change of any quantity per unit length in the direction of its maximum growth; G. in biology is a quantitative change in morphol or functional (including biochemical) properties along one of the axes of the body, organ or cell at any stage of their development. G., reflecting a change in any physiol, indicator (eg, metabolic rate), is called physiol, gradient (see Physiological gradient). When considering various biol, processes are more often encountered with electric field hydrolysis, concentration hydrolysis, osmotic hydrolysis, hydrostatic hydrostatic hydrolysis, and temperature hydrostatic hydrodynamics.
The electric field gradient in biological objects arises as a result of the movement of ions inside cells and tissues or due to the application of an external source of electric field, for example, during galvanization (see Galvanization, Electrophoresis). Particularly large values of the G. electric field occur on biol membranes. So, with a membrane thickness of approx. 10 nm and when the potential changes by 10, the electric field gradient across it will be 104 V/cm. Such a significant change in the internal electric field of the membrane can lead to a change in its polarization and the degree of ordering of its structure. There is a threshold value of the G. potential, at which the cells generate an action potential (see Bioelectric potentials, Excitation).
A concentration gradient in living tissues occurs when there is a significant difference in the concentration of ions in the internal and external environment, for example, a high internal concentration of potassium ions and a low concentration of sodium and chlorine ions. Thus, inside the fiber of the rat heart muscle there are 140 µmol of potassium ions and 13 µmol of sodium ions per 1 g of intracellular water. The external environment contains 2.7 µmol of potassium ions and 150 µmol of sodium ions. The concentration of potassium ions can be explained by the existence of the so-called. Donnan equilibrium (see Membrane equilibrium) on both sides of the biol, membrane. In this case, non-diffusing anions (for example, anions of protein macromolecules) cause an uneven distribution of the concentration of both anions (for example, C -) and cations (for example, K +) on both sides of the membrane. The existence of concentration gas of sodium ions cannot be explained by the Donnan equilibrium, and the transfer of sodium ions against concentration gas is explained by the existence of active transport of ions (see). Concentration G. of ions can also arise as a result of metabolic processes. As a result, all processes of redistribution of ions on different sides of the biol membrane lead to the emergence of resting potentials (see Bioelectric potentials).
The entry and exit of various substances from cells occurs due to the presence of G. their concentration. The rate of diffusion of substances is determined by the ratio: dn/dt =Dq grad C, where n is the number of molecules diffusing through the surface q, D is the coefficient. diffusion, grad C - concentration gradient; The diffusion coefficient is determined by the viscosity of the medium and the size of the molecules of the substance. The difference in the rate of diffusion of cations and anions (their mobility) leads to the appearance of a diffusion potential φ, which arises at the boundary of two contacting solutions and is described by the Nernst equation:
where U is the mobility of the cation, V is the mobility of the anion, C1 and C2 are the concentration of the electrolyte in two contacting solutions; R - gas constant, T - absolute t°, n - ion charge, F - Faraday number. The diffusion potential is minimal when the mobility of the cation and anion is equal or close, for example, in the case of a KCl solution. Therefore, this electrolyte is used in biology and medicine as a liquid conductor during galvanization, electrophoresis, etc.
The osmotic gradient characterizes the difference in the osmotic pressure (see) in the solvent-solution system, separated by a semi-permeable membrane, i.e., permeable to solvent molecules, but impermeable to the solute. Osmotic pressure is defined as the amount of force that must be applied to the solution in order to stop the movement of the solvent towards the solution. When the osmotic pressure in the external environment of the cell changes (for example, when it increases), water will enter the cell; the rate of water flow will be proportional to osmotic fluid (between the internal and external environment of the cell). Thus, for erythrocytes, the rate of water penetration is 2.5 µm 3 /ms 2 -min-atm. The osmotic pressure of the blood of higher animals is approx. 40 mm water. Art. and makes up a small part of the total blood pressure. If protein or salt metabolism is disrupted, the osmotic pressure also changes; for example, when it increases, water will enter the tissue, causing edema (see).
The hydrostatic gradient characterizes the pressure difference between the external and internal environment of a cell, the whole organism or its individual parts. Thus, the work of the heart leads to the appearance of a hydrostatic gradient. In the arterial part of the circulatory system, positive hydrostatic pressure occurs, in the venous part - negative (see Blood pressure). Hydrostatic pressure can compensate for osmotic pressure, which occurs in the capillaries of the circulatory system. With the growth of hydrostatic blood pressure (for example, with hypertension), the release of water from the bloodstream into the tissue increases, which can lead to edema.
The temperature gradient, which arises as a result of the temperature difference inside and outside the cell, significantly affects almost all life processes. Thus, the rate of diffusion of electrolytes increases by 30-40% with an increase in temperature by 10°. The electrical conductivity of cells increases by approximately the same amount. Heat transfer is proportional to the temperature on both sides of the surface; in this case Q = -λgrad T, where Q is the amount of heat transferred through the heat-conducting surface, λ is the coefficient. thermal conductivity, T - absolute temperature. The main source of heat in the human and animal bodies are exothermic processes that occur during the work of muscles and internal organs. Heat dissipation (eg from the surface of the human body) can also occur through convection, radiation and evaporation. All these processes accelerate with increasing temperature G.
Bibliography: Bayer V. Biophysics, trans. from German, M., 1962; Biophysics, ed. B. N. Tarusova and O. R. Collier, M., 1968; Pasynsky A. G. Biophysical chemistry, M., 1968.
Yu. M. Petrusevich.
Concentration gradient or concentration gradient is a vector physical quantity characterizing the magnitude and direction of the greatest change in the concentration of a substance in the environment. For example, if we consider two regions with different concentrations of a substance, separated by a semi-permeable membrane, then the concentration gradient will be directed from the region of lower concentration of the substance to the region with higher concentration.Definition
The concentration gradient is directed along the path l, corresponding to the normal to the isoconcentration surface (semipermeable membrane). Concentration gradient value equal to the ratio of the elementary change in concentration dC to the elementary path length dl :
At a constant concentration gradient C along the way l :
Here C 1 And C 2- initial and final concentration value along the path length l(normal to the isoconcentration surface).
The unit of measurement of the concentration gradient in the International System of Units (SI) is the value −4 (mol/m 4 or kg/m 4), as well as its fractional or multiple derivatives.
see also
Write a review about the article "Concentration gradient"
Literature
- Antonov V.F., Chernysh A.M., Pasechnik V.I. Biophysics - M.: VLADOS, 2000, p. 35. ISBN 5-691-00338-0
- Trifonov E. V.- St. Petersburg: 2011.
An excerpt characterizing the Concentration Gradient
I informed him about this. Please instruct Leppich to pay careful attention to the place where he descends for the first time, so as not to make a mistake and not fall into the hands of the enemy. It is necessary that he coordinate his movements with the movements of the commander-in-chief.]Returning home from Vorontsov and driving along Bolotnaya Square, Pierre saw a crowd at Lobnoye Mesto, stopped and got off the droshky. It was the execution of a French cook accused of espionage. The execution had just ended, and the executioner was untying a pitifully moaning fat man with red sideburns, blue stockings and a green camisole from the mare. Another criminal, thin and pale, stood right there. Both, judging by their faces, were French. With a frightened, painful look, similar to that of the thin Frenchman, Pierre pushed through the crowd.
- What is this? Who? For what? - he asked. But the attention of the crowd - officials, townspeople, merchants, men, women in cloaks and fur coats - was so greedily focused on what was happening at Lobnoye Mesto that no one answered him. The fat man stood up, frowning, shrugged his shoulders and, obviously wanting to express firmness, began to put on his doublet without looking around him; but suddenly his lips trembled, and he began to cry, angry with himself, as adult sanguine people cry. The crowd spoke loudly, as it seemed to Pierre, in order to drown out the feeling of pity within itself.
- Someone’s princely cook...
“Well, monsieur, it’s clear that Russian jelly sauce has set the Frenchman on edge... it’s set his teeth on edge,” said the wizened clerk standing next to Pierre, while the Frenchman began to cry. The clerk looked around him, apparently expecting an assessment of his joke. Some laughed, some continued to look in fear at the executioner, who was undressing another.
Pierre sniffed, wrinkled his nose, and quickly turned around and walked back to the droshky, never ceasing to mutter something to himself as he walked and sat down. As he continued on the road, he shuddered several times and screamed so loudly that the coachman asked him:
- What do you order?
-Where are you going? - Pierre shouted at the coachman who was leaving for Lubyanka.
“They ordered me to the commander-in-chief,” answered the coachman.
