Model lipid membranes. Active transport of substances
1.Experiments of Pfefer, Hardy-Fischer, Overton. The nature of the cell membrane and the alternative to the cell membrane.
2. The method of fluorescent probes in the study cell membranes.
3. The specific electrical capacitance of the axon membrane, measured by an intracellular electrode, was 0.5 μF/cm 2 . using the flat capacitor formula, determine the thickness of the hydrophobic layer of the membrane. Ε of lipids is considered equal to 2.
4.Mechanism of generation of action potential of cardiomycetes.
5. Method of spin probes in the study of cell membranes.
6. What is the distance on the surface of the erythrocyte membrane that a phospholipid molecule travels in 1 second as a result of lateral diffusion? The coefficient of lateral diffusion is taken equal to 10 -12 m 2 /s. compare with the circumference of an erythrocyte with a diameter of 8 µm.
7. Structure of the ion channel.
8.Method of differential microcalorimetry.
9. During the phase transition of membrane phospholipids from a liquid-crystal state to a gel, the thickness of the bilayer changes. How will the capacitance of the membrane change in this case?
10. Ion channels of cell membranes.
11. X-ray structural analysis in the study of cell membranes. Principles and examples.
12. During the phase transition of membrane phospholipids from the liquid-crystal state to the gel, the thickness of the bilayer changes. How will the electric field strength in the membrane change in this case?
13. Ionic currents in the axon. Hodgkin-Huxley model.
14.Methods for studying membrane permeability.
15. With the help of spin-labeled phospholipid molecules, the thickness gradient of viscosity in the membrane was established. Describe the experiment.
16.Mechanism of action potential generation.
17. Application of conductometry in the study of membranes. Fricke's experiments.
18. Where the viscosity of the hydrophobic layer is higher: at the membrane surface or in its thickness. How is it installed?
19. Distribution of a nerve impulse along an excitable fiber.
20. Electrokinetic phenomena in cells and suspensions.
21. How will the facilitated diffusion of potassium ions with the participation of the valinomycin molecule change after the phase transition of membrane lipids from a liquid-crystalline state to a gel?
22. Action potential. physical mechanism.
23. Electrosmosis in living cells and tissues.
24. Will there be an osmotic effect (swelling in hypotonic and wrinkling in hypertonic solutions) during the accumulation of sodium ions according to the antiport scheme?
25. Resting potential. His nature.
26. The nature of osmosis in living cells.
27. Will there be an osmotic effect (swelling in hypotonic and wrinkling in hypertonic solutions) during the accumulation of sodium ions according to the symport scheme?
28. Nature of bioelectric potentials.
29. A cell is like an osmometer. An example of determining the isotonicity of a solution using live cells.
30. Show that the Nernst-Planck equation is reduced to the Fick equation for the case of diffusion of uncharged particles.
31. Differences between protein channels and lipid pores.
32. Nature of dead cells settling. Fiz.khim osonvy method ESR.
33. The enzyme Na + -K + - ATPase in the plasma membrane of the erythrocyte has completed six cycles. How many sodium and potassium ions were actively transported? How much energy was spent in this case, if the hydrolysis of one mole of ATP is accompanied by the release of 33.6 kJ?. The coupling efficiency is assumed to be 100%.
34.mechanism of membrane permeability for water molecules. The kink hypothesis.
35. NMR spectroscopy in the study of membranes. Examples and principles.
36. Three ion pumps are known in cell membranes: sodium-potassium, proton, and calcium. How is the active transport of sugar and amino acids carried out?
37. Model of pore formation during phase transition.
38.Methods for measuring microviscosity in membranes.
39. Is simultaneous transmembrane transfer of potassium and sodium ions possible according to the symport scheme?
40. electrical breakdown of membrane lipids.
42.methods of spectral probes.
43. Is simultaneous transmembrane transfer of potassium and sodium ions possible according to the antiport scheme?
44. model of the critical lipid pore.
45. application of ion-selective electrodes in the study of membrane permeability.
46. Is simultaneous transmembrane transfer of potassium and sodium ions possible according to the uniport scheme?
47. lipid pores in the light of membrane stability.
48. methods of erythrograms. their informational value.
49. What transport of ions creates a membrane potential difference: passive or active?
50. Mechanism and patterns of secondary active transport of ions.
51. Experimental criteria for facilitated diffusion.
52. What is more the speed of propagation of an electrical signal along the wires of a marine telegraph or the speed of propagation of a nerve impulse along the axon membrane? Why?
53. Electrogenic ion pumps.
54. Cell fractionation methods.
55. What is the biophysical mechanism of action of the local anesthetic tetraylammonium?
56. Ussing's experience and scheme.
57. The nature of the forces of lipid-lipid interaction in the membrane. Research methods.
Calendar thematic plan for the discipline
"Molecular organization biological membranes»
2011/2012 academic year year (4th year, 7th semester of the All-Russian Biophysics Facility)
| date | No. p / p | Type and name of the training module | Educational and methodological support of the training module |
| LECTURES: | |||
| Biological membranes as universal structural and functional formations of living systems. | Lecture summary. | ||
| Structural organization of biomembranes. | Lecture summary. | ||
| Membrane proteins and lipids. | Lecture summary. | ||
| Protein-lipid interactions. | Lecture summary. | ||
| Dynamic properties of membranes. | Lecture summary. | ||
| Modeling the structure of membranes. | Lecture summary. | ||
| Membrane structure calculations | Lecture summary. | ||
| TOTAL - 14 hours | |||
| Practical lessons * | |||
| Calculations of electrical capacitance and impedance of membranes. | Computer class of the department. | ||
| Determination of the thickness of the erythrocyte membrane by electrical conductivity. | Computer class of the department. | ||
| Study of the mechanical strength of erythrocyte membranes. | Computer class of the department. | ||
| Study of the effect of cholesterol on the deformability of erythrocyte membranes. | Computer class of the department. | ||
| Calculations of the strength of erythrocyte membranes. | Computer class of the department. | ||
| Action research magnetic field on the mechanical properties of erythrocyte membranes | Computer class of the department. | ||
| Total - 22 hours |
* - each practical lesson calculated for 4 hours.
Approved at a meeting of the department _____________________________________________
active transport - the transport of molecules and ions, which occurs at a cost chemical energy in the direction from smaller values to larger ones.
In this case, neutral molecules are transferred to a region of higher concentration, and ions are transferred against the forces acting on them from the electric field. Thus, active transport carries out the transfer of substances in the direction opposite to the transport, which should have occurred under the action of gradients (primarily concentration and electric). Energy is obtained through the hydrolysis of molecules of a special chemical compound - adenosine triphosphoric acid (ATP). It has been experimentally established that the decay energy of one ATP molecule is sufficient to bring out three sodium ions and introduce two potassium ions into the cell. The scheme of active transport is shown in Fig. 13.
Having captured a potassium ion from the external environment with one active center, and a sodium ion from the internal environment with another, the system, consuming ATP, rotates 180 ° inside the membrane. The sodium ion is outside the cell and is separated there, and the potassium ion gets inside and is also released, after which the protein molecule takes its original position, and everything starts all over again.
Due to active transport, the cell maintains a high concentration of potassium and a low concentration of sodium inside itself. In this case, ions can move against their concentration gradient (an analogy with a gas: pumping gas from a vessel with low pressure to a vessel with high pressure).
Fig.13. Active transport scheme
Active transport of substances across biological membranes is of great importance. Due to active transport, concentration gradients, electrical potential gradients, pressure gradients, etc., are created in the body that support life processes, i.e., from the point of view of thermodynamics, active transport keeps the body in a non-equilibrium state, supports life.
The existence of active transport of substances through biological membranes was first proved in the experiments of Ussing (1949) using the example of the transfer of sodium ions through the skin of a frog (Fig. 14).
Rice. 14. Ussing's experiment scheme (A - ammeter, V - voltmeter, B - battery, P - potentiometer)
The Ussing experimental chamber, filled with normal Ringer's solution, was divided into two parts with freshly isolated frog skin. In Fig. 14 on the left - the outer mucosal surface of the skin, on the right - the inner serous. Flows of sodium ions through the skin of the frog were observed: from left to right from the outer to the inner surface and from right to left - from the inner to the outer surface.
On the skin of a frog that shared Ringer's solution, a potential difference arose, and the inner side of the skin had a positive potential with respect to the outer one. The installation had a voltage compensation unit, with the help of which the potential difference on the frog's skin was set to zero, which was controlled by a voltmeter. In addition, the same concentration of ions was maintained on the outer and inner sides. Under these conditions, if the transfer of sodium ions through the skin of a frog was determined only by passive transport, then the flows of sodium ions should be equal to each other, and there should be no current in the circuit.
However, it was found that under the conditions of the experiment (the absence of electric potential and concentration gradients), an electric current flows through the skin of the frog, therefore, one-way transfer of charged particles occurs. It has been established that current flows through the skin from external environment to the inside. It has been shown by the tagged atom method that the inward flow of sodium is greater than the outward flow.
To do this, radioactive isotopes of Na 22 were included in the left solution of the experimental chamber, and Na 24 in the right one. The Na 22 isotope decays with the emission of hard γ-quanta. The decay of Na 24 is accompanied by soft β radiation. Registration of γ - and β - radiation showed that the flow of Na 22 is greater than the flow of Na 24 . These experimental data provided irrefutable evidence that the transfer of sodium ions through the skin of a frog does not obey the passive transport equation. Therefore, active transfer takes place. Further experiments showed that the depletion of ATP reserves in the skin of a frog leads to a complete stop of the unidirectional flow of sodium ions.
3. The purpose of the activities of students in the classroom:
The student must know:
1. The role of the membrane in the functioning of the cell.
2. Structure, structure and models of membranes.
3. Membrane functions.
4. Physical properties of membranes.
5. Fick's equation.
6. Nernst-Planck equation.
7. Types of passive transport of particles through the membrane.
8. Active transport of particles through the membrane.
The student must be able to:
1. Explain the structure of the membrane.
2. Explain artificial models of membranes.
3. Explain the mechanism of passive transport across the membrane.
4. Explain the mechanism of active transport across the membrane.
5. Solve situational problems.
1. The structure of biological membranes.
2. Liquid-mosaic model of the membrane.
3. Artificial models of membranes.
4. The main functions of the cell membrane.
5. Physical properties of membranes.
6. Transfer of molecules (atoms) through the membrane. Fick's equation.
7. Transfer of ions through membranes. Nernst-Planck equation.
8. Varieties of passive transfer of molecules and ions through membranes.
9. Active transport. Ussing's experience.
10. Solution of situational problems.
5. List of questions to check the initial level of knowledge:
1. What are biological membranes?
2. What is the basis of the membrane?
3. What are physicochemical (artificial) membrane models used for?
4. Describe the fluid mosaic model of the membrane.
5. What is lateral diffusion? flin flop transition?
6. What are the main functions of the membrane and what are they?
7. Write down the Fick and Nernst-Planck equations. What processes do they describe?
8. What is called mobility?
9. What is passive transport? What are the types of passive transport?
10. What is active transport? By what means is it carried out?
11. What is the importance of active transport of substances?
12. Explain the phenomena of matter and charge transfer through a membrane.
13. What will happen if the cage is placed in clean water?
6 . List of questions to check the final level of knowledge:
1. Describe model lipid membranes. Where are they used?
2. Describe physical properties membranes.
3. During the phase transition of membrane phospholipids from the liquid-crystal state to the gel, the thickness of the bilayer changes. How will the capacitance of the membrane change in this case? How will the electric field strength in the membrane change?
4. Apply the Fick equation to a biological membrane.
5. Write down and explain the Nernst-Planck equation.
6. Show that the Nernst-Planck equation reduces to the Fick equation for the diffusion of uncharged particles.
7. Describe the types of passive transport.
8. The permeability of cell membranes for water molecules is approximately 10 times higher than for ions. What happens if the concentration of an osmotically active substance (for example, Na + ions) is increased in an isotonic aqueous solution in which erythrocytes are located?
9. Describe Ussing's experience.
7. Solve problems:
1. What is the distance on the surface of the erythrocyte membrane that a phospholipid molecule travels in 1 second as a result of lateral diffusion? The coefficient of lateral diffusion is taken equal to 10 -12 m 2 /s. Compare with the circumference of an erythrocyte with a diameter of 8 µm.
2. The specific electrical capacitance of the axon membrane, measured by an intracellular microelectrode, was 0.5 μF/cm 2 . Using the flat capacitor formula, estimate the thickness of the hydrophobic layer of a membrane with a dielectric constant of 2.
3. The thickness of the double layer at the membrane-electrolyte interface is characterized by the Debye radius δ . Determine δ for the case when in the electrolyte solution surrounding the membrane, there are only potassium ions with a concentration of: 1) 10 -5 mol/l; 2) 10 -2 mol/l.
4. Find the Debye shielding radius created by calcium ions present in the solution with a concentration of 10 -5 mol/l and sodium ions with a concentration of 10 -4 mol/l. How will it change δ, if the solution contains only calcium ions at a concentration of 10 -4 mol/l?
5. The critical radius of a lipid pore in a membrane depends on the edge tension of the pore, the surface tension of the membrane, and the membrane potential. Derive a formula for the critical pore radius. Calculate the critical pore radius in the absence of a membrane potential. Adopt pore edge tension 10 -11 N, lipid bilayer surface tension 0.3 mN/m.
6. Molar concentration of oxygen in the atmosphere with a= 9 mol/m. Oxygen diffuses from the surface of the body of insects inward through tubes called tracheae. The length of the middle trachea is approximately h= 2 mm, and its cross-sectional area S\u003d 2 ∙ 10 -9 m 2. Assuming that the oxygen concentration inside the insect ( With) is two times less than the concentration of oxygen in the atmosphere, calculate the diffusion flux through the trachea. Oxygen diffusion coefficient D\u003d 10 -5 m 2 / s.
7. The double phospholipid layer likens the biological membrane to a capacitor. The membrane material is a dielectric with permittivity ε = 4. Potential difference between membrane surfaces U= 0.2 V at thickness d= 10 nm. Calculate the capacitance of 1 mm 2 of the membrane and the electric field strength in it.
8. The surface area of the cell is approximately equal to S\u003d 5 ∙ 10 -10 m 2. The specific electrical capacitance of the membrane (capacity per unit area) is Court\u003d 10 -2 F / m 2. In this case, the intercellular potential is U= 70 mV. Determine: a) the magnitude of the charge on the membrane surface; b) the number of monovalent ions that form this charge.
9. The enzyme Na + - K + - ATPase in the plasma membrane of the erythrocyte has completed six cycles. How many sodium and potassium ions were actively transported? How much energy was spent in this case, if the hydrolysis of one mole of ATP is accompanied by the release of 33.6 kJ? The efficiency of the process of energy conjugation is considered 100%.
8. Independent work students:
According to the textbook by Antonov V.F. et al. (§ 15.4.) Familiarize yourself with physical methods determination of the membrane thickness.
9. Chronocard of the lesson:
1. Organizing time- 5 minutes.
2. Analysis of the topic - 50 min.
3. Solution of situational problems - 40 min.
4. Current control of knowledge - 30 min
5. Summing up the results of the lesson - 10 min.
10. List of educational literature for the lesson:
1. Remizov A.N., Maksina A.G., Potapenko A.Ya. Medical and biological physics, M., "Drofa", 2008, §§ 11.1, 11.2, 11.5, 11.6.
Liposomes, or phospholipid vesicles (vesicles), are usually obtained by swelling dry phospholipids in water or by injecting a lipid solution into water. In this case, self-assembly of the bimolecular lipid membrane occurs. The Gibbs energy minimum corresponds to a closed spherical one-lamellar form of the membrane. In this case, all nonpolar hydrophobic tails are inside the membrane and none of them comes into contact with polar molecules water (Fig. 1.11). However, non-spherical multilamellar liposomes, consisting of several bimolecular layers, are more often obtained - multilayer liposomes.
Rice. 1.11. Scheme of the structure of a single-layer liposome
The individual bimolecular layers of the multilayer liposome are separated by an aqueous medium. The thickness of the lipid layers is, depending on the nature of the lipids, 6.5 - 7.5 nm, and the distance between them is 1.5 - 2 nm. The diameter of multilayer liposomes ranges from 60 nm to 400 nm or more.
Single-layer liposomes can be obtained by various methods, for example, from a suspension of multi-layer liposomes, if they are treated with ultrasound. The diameter of single-layer liposomes obtained by this method is 25-30 nm. Other methods have also been developed for obtaining single-layer liposomes, including those with a diameter of up to 400 nm or more.
Liposomes are in some way the prototype of the cell. They serve as a model for studying various properties of cell membranes.
Liposomes have found direct application in medicine. For example, it is possible to encapsulate a drug within liposomes and use it as a phospholipid microcapsule to deliver the drug to specific organs and tissues. Liposomes are non-toxic (with the right selection of lipids), are completely absorbed by the body, and are able to overcome some biological barriers. So, insulin enclosed in a liposome is protected from the action of digestive enzymes. Currently, the possibility of administering this drug in liposomes orally is being investigated, which can save diabetics from the need for systematic injections. Work is underway to develop methods of liposomal therapy for tumors, enzymatic deficiency, and atherosclerosis. The possibility of targeted delivery of a drug contained in liposomes to a diseased organ or even to a diseased area (in particular, to the affected area of the heart) is being studied.
To do this, a protein molecule is attached to the liposome - an antibody to the corresponding membrane antigen of the target organ. Liposomes with blood flow are carried throughout the body and linger when they are near the target organ.
Despite the tempting prospects of liposomal therapy, there are still many outstanding issues.
Rice. 1.12. Formation of a squamous bilayer lipid membrane
Flat bilayer lipid membranes (BLM) - another type of model membranes. Such membranes are produced on small holes with a diameter of about 1 mm in a plastic plate (for example, fluoroplastic) immersed in aquatic environment. A drop of a lipid solution (in alcohol, chloroform, heptane, or other solvents) is applied to the hole. The solvent diffuses from the solution into the water and a lipid film remains on the hole. This film thins spontaneously until a bimolecular layer about 6 nm thick is formed. Excess lipid is collected in the form of a rim-torus at the edges of the hole (Fig. 1.12).
Flat lipid membranes, along with liposomes, are widely used as models for studying the electrical properties of the membrane, their permeability and other scientific studies. With the help of model membranes, a number of biological membrane functions are studied, including the barrier function (for example, permeability selectivity - good permeability for water and poor permeability for ions). Biological transport can be simulated by introducing carrier molecules into the model membrane.
control questions, tasks, assignments
1. The specific electrical capacitance of the axon membrane, measured by an intracellular microelectrode, was found to be 0.5 microfarad/cm 2 . Using the flat capacitor formula, estimate the thickness of the hydrophobic layer of a membrane with a dielectric constant of 2.
2. What is the distance on the surface of the erythrocyte membrane that a phospholipid molecule travels in 1 second as a result of lateral diffusion? Take the lateral diffusion coefficient equal to 10~12 m 2 /s. Compare with the circumference of an erythrocyte with a diameter of 8 µm.
3. During the phase transition of membrane phospholipids from the liquid-crystal state to the gel, the thickness of the bilayer changes. How will the capacitance of the membrane change in this case? How will the electric field strength in the membrane change?
4. Using spin-labeled phospholipid molecules, the viscosity gradient across the membrane thickness was established. Describe the experiment. Where is the viscosity higher: at the surface of the membrane or in its center?
routine monitoring tests
1.1. Biological membrane thickness:
1. 10 A 3.0.1 µm
2. 10 nm 4. 10 µm
1.2. The fluid mosaic model of a biological membrane includes:
1. protein layer, polysaccharides and surface lipids!
2. lipid monolayer and cholesterol
3. lipid bilayer, proteins, microfilaments
4. lipid bilayer
1.3. The lipid part of the biological membrane is located in the following physical condition:
1. liquid amorphous
2. solid crystalline
3. solid amorphous
4. liquid crystal
1.4. Specific electrical capacitance of the axon membrane:
1. 0.5 10 -4 F/m2 3. 0.5 10 -2 F/cm2
2. 0.5 Yu -2 F / m 2 4. 0.5 10 -12 F / m 2
1.5. The characteristic time for the transfer of a phospholipidoph molecule from one equilibrium position to another during their diffusion:
lateral flip-flop
1. 10 -7 – 10 -8 ~1 hour
2. 10 -10 - 10 -12 10 -7 - 10 -8 s
3. 1 - 2 hours 10 - 50 s
1.6. The phase transition of the lipid bilayer of membranes from the liquid-crystal state to the gel is accompanied by:
1.Thinning membrane
2. membrane thickness does not change
3. Thickened membrane
CHAPTER 2. TRANSPORT OF SUBSTANCES THROUGH BIOLOGICAL MEMBRANES
Living systems at all levels of the organization - open systems. Therefore, the transport of substances through biological membranes is a necessary condition for life. The transfer of substances through membranes is associated with the processes of cell metabolism, bioenergetic processes, the formation of biopotentials, the generation of a nerve impulse, etc. Violation of the transport of substances through biomembranes leads to various pathologies. Treatment is often associated with the penetration of drugs through cell membranes. The effectiveness of the drug largely depends on the permeability of the membrane for it.
Great importance to describe the transport of substances has the concept of electrochemical potential.
The chemical potential of a given substance μ to is a value numerically equal to the Gibbs energy per mole of this substance. Mathematically, the chemical potential is defined as a partial derivative of the Gibbs energy G by the amount of k-ro substance, at a constant temperature T, pressure P and the amounts of all other substances m 1 (l≠k):
For a dilute solution of the concentration of substance C:
where μ Q is the standard chemical potential, numerically equal to the chemical potential of a given substance at its concentration of 1 mol/l in solution.
The electrochemical potential μ is a value numerically equal to the Gibbs energy G per one mole of a given substance placed in an electric field.
For dilute solutions
where F = 96500 C/mol is the Faraday number, Z is the charge of the electrolyte ion (in elementary units charge), φ is the potential of the electric field, T [K] is the temperature.
The transport of substances across biological membranes can be divided into two main types: passive and active.
2. What is the distance on the surface of the erythrocyte membrane that a phospholipid molecule travels in 1 second as a result of lateral diffusion? Take the lateral diffusion coefficient equal to 10–12 m2/s. Compare with the circumference of an erythrocyte with a diameter of 8 µm.
3. During the phase transition of membrane phospholipids from the liquid-crystal state to the gel, the thickness of the bilayer changes. How will the capacitance of the membrane change in this case? How will the electric field strength in the membrane change?
4. How will the electrical capacitance of the membrane (specific) change during its transition from the liquid-crystal state to the gel, if known
5. Calculate the time of settled life and the frequency of jumps from one membrane layer to another lipid membranes of the sarcoplasmic reticulum, if the coefficient of lateral diffusion D=12 μm 2 /s, the area occupied by one molecule of phospholipid A=0.7 nm 2.
6. Calculate the permeability coefficient for the substance whose flux through the membrane is mol/m. The concentration of a substance inside the cell, and outside - mol / l.
7. How many times the intracellular concentration of potassium ions must exceed the external one so that the resting potential is 91mV. Calculate the cell temperature.
8. Calculate the distribution coefficient K for a substance if, with a membrane thickness of 10 nm, the diffusion coefficient is 7.2 * 10 cm, and the permeability coefficient is 14 cm / s.
9. The difference in the concentration of substance molecules on the membrane of a certain cell is 48 mmol / l, the distribution coefficient between the membrane and the environment is 30, the diffusion coefficient is 1.5 * 10, the flux density is 25 mol / m. Calculate the thickness of this membrane.
10. Find the permeability coefficient of the Mycoplasma plasma membrane, for formamide, if, with a difference in concentrations of this substance inside and outside the membrane, equal to 0.5 * 10, its flux density through the membrane is 8 * 10 cm / s.
17. The critical radius of a lipid pore in a membrane depends on the edge tension of the pore , the surface tension of the membrane and the membrane potential . Derive a formula for the critical pore radius. Calculate the critical pore radius in the absence of a membrane potential. Take the edge tension of the pore 10 - 11 N, the surface tension of the lipid bilayer 0.3 mN/m.
18. During the phase transition of membrane phospholipids from the liquid-crystal state to the gel, the thickness of the bilayer changes. How will the capacitance of the membrane change in this case? How will the electric field strength in the membrane change?
19. During the phase transition of membrane phospholipids from the liquid-crystal state to the gel, the thickness of the bilayer changes. How will the capacitance of the membrane change in this case? How will the electric field strength in the membrane change?
20. How will the electrical capacitance of the membrane (specific) change during its transition from the liquid crystal state to the gel, if it is known that in the liquid crystal state the thickness of the hydrophobic layer is 3.9 nm, and in the gel state - 4.7 nm. Dielectric constant of lipids 2.
21. The osmotic pressure of human blood is 0.77 MPa. How many moles of NaCl salt should an isotonic saline solution contain in 200 ml of water at a temperature of 37 0 C?
22. When the NMR spectrum of the same sample was re-registered, the temperature changed, the lines of the spectrum became narrower. In which direction did the temperature change: decreased or increased?
23. Find length electromagnetic wave, at which EPR occurs in a magnetic field with a magnetic induction of 0.3T. Take the Lande factor equal to two.
24. A current flows along a contour with a radius of 0.5 m. Find the strength of this current if it is known that the magnetic moment of circuit B.
26. Determine the thermal radiation power of a naked person with S = 1 m 2 of body surface, if skin temperature t 1 = 30 0 C, environment- t 2 \u003d 20 0 C. Skin absorption coefficient k \u003d 0.9
27. The radiation intensity of the human body increased by 2.62%. By what percent did the temperature rise?
28. Determine the wavelength corresponding to the maximum spectral density of the energy luminosity of the human body, considering it a gray body. Skin temperature t=30 0 C.
29. Determine the natural molar absorption index of substances if, at its concentration in a solution of c \u003d 0.03 mol / l, the optical density of the solution is D \u003d 1. Cuvette length l= 2 cm.
30. By observing the movement of red blood cells in a capillary under a microscope, you can measure the speed of blood flow (). average speed blood flow in the aorta is . Based on these data, determine how many times the sum of all functioning capillaries is greater than the cross section of the aorta.
31. Calculate the resolution limit z of an electron microscope, if the accelerating voltage in it is U=100 kV, the aperture angle is u=10 -2 rad.
32. Calculate blood viscosity at normal hematocrit (c=45%) if plasma viscosity is
33. Calculate the maximum minute volume Qmax of blood at which the blood flow in the aorta remains laminar. Aortic diameter d=2 cm, blood viscosity , density , critical Reynolds number Re kr =2000.
34. The speed of propagation of the pulse wave through the artery is v=10 m/s. Determine the modulus of elasticity E of the artery, if its wall thickness h=0.7 mm, inner diameter d=8 mm, blood density
35. The radius of the aorta is 1.0 cm; the speed of blood flow in the aorta is 30 cm/s. What equals speed blood flow in the capillaries, if the total cross-sectional area of the capillaries is 2000 cm 2. (The diameter of each capillary is taken as , and the number of capillaries is more than a million).
36. In medicine, the Doppler effect is used to determine the speed of movement of individual biological structures (for example, blood, heart valves). How is the change in the frequency of an ultrasonic signal reflected from a moving object related to its speed?
37. A force F = 10 N is applied to the piston of a horizontally located syringe. Determine the speed v of the drug outflow from the syringe needle if the density of the drug is , the piston diameter is d = 7 mm, and its area is much larger than the cross-sectional area of the needle.
38. With what speed v does an air bubble with a diameter of d = 4 mm float up in a vessel filled with glycerin? Kinematic viscosity glycerine, its density is much greater than that of air.
39. In some diseases, the critical Reynolds number in the vessels becomes equal to 1160. Find the speed of blood movement at which the transition from laminar to turbulent flow is possible in a vessel with a diameter of 2 mm.
40. The level of sound volume is 120 phon, and a quiet conversation - at the same distance - 41 phon. Determine the ratio of intensities.
42. Sound intensity 10-2 W/m2. Find the sound pressure if the acoustic resistance of the medium (air) is 420 kg/m2s.
43. Determine the amplitude value of the sound pressure for a pure tone with a frequency of 1000 Hz, at which the tympanic membrane may rupture if the rupture occurs at a volume level L E = 160 phon. (The answer is expressed in pascals and in atm.)
44. The electric heater in the installation for the thermal treatment of medicinal raw materials evaporates 1 liter of water in 10 minutes, viscous at a temperature of 20 0 C. Determine the length of the nichrome wire with a cross section of 0.5 mm 2, given that the installation is powered by a voltage of 120 V and its efficiency is 80% ?
45. The intensity of light passing through a solution of aspirin in a non-absorbing solvent is reduced by a factor of three due to absorption. The concentration of aspirin molecules n 0 =10 20 m -3 . The path of light in the solution = 150 mm. Determine the effective absorption cross section of aspirin.
46. Determine the phase difference in the pulse wave between two points of the artery located at a distance from each other, considering the speed of the pulse wave equal to v = 10 m / s, the heart oscillations are harmonic with a frequency = 1.2 Hz.
49. To heat the muscle tissue, a voltage is applied to the flat electrodes with an amplitude U 0 \u003d 250 V and a frequency \u003d 10 6 Hz. The active resistance of this section of the circuit R=10 3 Ohm; capacitance C= F. Determine the amount of heat released in the volume of tissue between the electrodes during the oscillation period T and during the procedure t=10 min.
50. Iontophoresis is used to introduce drugs into the human body. Determine the number of singly ionized ions of the drug substance administered to the patient over time t= 10 min at a current density of 0.05 mA/cm 2 from an electrode with an area of S=5 cm 2
EXAM QUESTIONS
biological membranes. Types of biological membranes and their functions.
Types of membrane lipids and their properties. Bilayer lipid structures.
Cholesterol. Dynamics of lipids in the membrane. Phase transitions in the membrane.
membrane proteins. Types and functions of membrane proteins.
The structure of biological membranes.
artificial membranes. Liposomes.
Methods for studying the structure of membranes.
Capillary phenomena, their significance in biology and medicine. gas embolism.
Transport of substances through biological membranes. Ways of penetration of substances into the cell.
Types of transport. simple diffusion.
Transport of nonelectrolytes across biological membranes.
Basic mechanisms of passive transport.
Ion transport. Ionic transport of substances in channels.
Mechanisms of permeability of biological membranes. Structure and functions of ion channels and carriers. Mechanisms of electrogenesis.
Active transport across biological membranes.
Molecular mechanisms of electrochemical potentials of membranes and propagation of a nerve impulse along an excitable fiber.
The concept of electrical excitability . Resting potentials .
Membrane potential measurement methods. Microelectrode technology.
action potential . The mechanism of generation and propagation of the action potential.
Methods for studying the molecular mechanisms of the electromechanical potentials of membranes.
Propagation of a nerve impulse along an excitable fiber.
Biomedical information sensors. Types of sensors.
Purpose and classification of sensors, characteristics.
Thermoelectric phenomena in metals and semiconductors.
Calibration of thermal sensors and determination of the temperature of a substance.
Electrodes for taking bioelectric signal.
Ionic currents in the Hodgkin-Huxley model.
Ion channels in cell membranes. Structure of the ion channel.
The mechanism of generation of the action potential of the cardiomyocyte.
membrane potentials. The action potential of the heart cell.
Physical basis of electrocardiography. The device, the principle of operation of the electrocardiograph .. Basic approaches to ECG recording.
ECG registration and principles of analysis.
Electroencephalography. Basic EEG rhythms. their functional significance.
Registration of EEG and principles of analysis. functional tests.
The main types of electrical activity of pyramidal neurons.
37. Energy levels of molecules (electronic, vibrational and rotational energy of molecules).
38. Electronic transitions in the absorption of light.
39. Absorption spectra of molecules of some biologically important compounds.
40. Methods for studying photobiological processes using spectra.
41. Device and principle of operation of spectrophotometers .
42. The study of spectrophotometric research methods for determining the concentration of substances in biological fluids.
43. Luminescence of biological systems.
44. Luminescence. Various types of luminescence.
45. Photoluminescence. Stokes' rule.
46. Fluorescence quantum yield. Triplet level and phosphorescence.
47. Photoluminescent qualitative and quantitative analysis of biological objects.
48. Fluorescent microscopy. Chemiluminescence, chemiluminescence generation mechanism
49. Primary stages of photobiological processes.
50. Spectra of photobiological action.
51. Study of products of primary photobiochemical reactions.
52. Free radical oxidation. Primary photochemical reactions of proteins.
53. Photochemical transformation of DNA.
54. Features of the action of high-intensity laser radiation on DNA.
55. Photoreactivation and photoprotection.
56. Action of ultraviolet light on biological membranes.
57. Photosensitized photobiological processes.
58. Study of biological objects in microscopy.
59. Special methods of microscopy of biological objects
60. Optical system of a microscope, building an image of an object.
61. The formula for the magnification of an optical microscope.
62. Biophysics of muscle contraction . Sliding thread model.
63. Biomechanics of the muscle. Hill equation.
64. Power of a single contraction. Simulation of muscle contraction.
65. Electromechanical interface
66. Circulatory system (arteries, veins). Mechanism of blood circulation
67. Movement of blood in large vessels.
68. Organization of blood flow in microvessels.
69. Movement of blood cells in capillaries.
70. Factors determining the rheological properties of blood.
71. Forms of orientation of erythrocytes in capillaries.
72. Hemodynamic patterns of blood flow through the vessels.
73. General physical and mathematical patterns of blood movement in the bloodstream.
74. Rheography of various organs and tissues . Methods for studying blood circulation.
75. Methods of registration and principles of analysis of the eographic curve. Integral and regional rheography.
76. Methods of indirect registration of shock and minute ejection. Computer integrated rheography.
77. Physical basis of the interaction of sound and biological tissues.
78. Classification of medical devices and devices.
79. Forms of energy that are converted in a measuring transducer.
80. Medical devices for therapeutic purposes.
81. Therapeutic electronic medical equipment.
82. Methods of high-frequency therapy (HF, UHF, microwave, etc.) and their biophysical effects.
83. The device of the UHF-therapy apparatus and its principle of operation.
84. Therapeutic technique based on the use of direct current
85. The device of the galvanization apparatus and its principle of operation. Physical basis of galvanization
87. Basic technical means of medical introscopy.
88. Designs of sensors and their main characteristics.
89. Devices for measuring the function of external respiration
90. Registration of movements chest during respiratory movements. Pneumography, spirometry, spirography.
List of practical skills
to register EEG., RG
to register ECG in standard leads;
be able to explain the genesis of ECG phenomena and methods for their detection.
learn to form an electrocardiographic diagnosis.
register physical parameters,
process measurement results using computing tools;
measure the concentration of substances using photometric instruments.
solve the problem of optimal pairing of a biological object and technical means in biomedical research;
to choose the right technical means in solving medical problems
Liposomes are, in some way, prototypes of cells. They serve as a model for studying the various properties of cell membranes.
Liposomes have found direct application in medicine. For example, it is possible to include a drug inside liposomes and use it as a phospholipid microcapsule to deliver the drug to certain organs and tissues. Liposomes are not toxic (with the right selection of lipids), are completely absorbed by the body, and are able to overcome some biological barriers. Thus, insulin enclosed in a liposome is protected from the action of digestive enzymes. Currently, the possibility of administering this drug in liposomes orally is being investigated, which may save diabetics from the need for systematic injections. Work is underway to develop methods of lposomal therapy for tumors, enzymatic deficiency, and atherosclerosis. The possibility of targeted delivery of a drug contained in liposomes to a diseased organ or even to a diseased area (in particular, to the affected area of the heart) is being studied.
To do this, a protein molecule, an antibody to the corresponding membrane antigen of the target organ, is attached to the liposome. Liposomes are circulated throughout the body with blood flow and are retained near the target organ.
Despite the promising prospects of liposomal therapy, there are still many unresolved issues. S~Ure
with Ryas. 1. 12. Formation of a flat bilayer lily membrane
Planar bielocular lipid membranes (BLMs) are another type of model membrane. Such membranes are obtained through small holes about 1 mm in diameter in a plate of plastic (for example, fluoroplast) immersed in an aqueous medium. A drop of a lipid solution (in alcohol, chloroform, heptaium or other solvents) is applied to the hole. The solvent diffuses through the solution into the water, leaving a lipid film behind the hole. This spit spontaneously thins until a bimolecular layer about 6 nm thick is formed. The extra line is collected in the form of a rim-torus at the edges of the hole (Fig. 1.12).
Flat lipid membranes, along with liposomes, are widely used as models for learning. electrical properties membranes, their permeability and other scientific research. With the help of model membranes, a number of functions of biological membranes are taught, including barrier functions (for example, permeability selectivity - good permeability for water and poor permeability for ions). Biological transport can be simulated by introducing carrier molecules into the model membrane.
CONTROL QUESTIONS, TASKS, TASKS
1. The specific electrical capacitance of the axon membrane, unmeasured by an intracellular microelectrode, turned out to be 0.5 microfarads / cm. Using the flat capacitor formula, estimate the thickness of the hydrophobic layer of the membrane with a dielectric constant of 2.
2. What is the distance on the surface of the erythrocyte membrane that a phospholipide molecule travels in 1 second as a result of lateral diffusion. Take the coefficient of lateral diffusion equal to 10 1e m "/s. Compare with the circle of an erythrocyte with a diameter of 8 microns.
3. During the phase transition of membrane phospholipids from the liquid-crystal state to the gel, the thickness of the bilayer changes. How does the electrical capacitance of the membraneu change in this case How does the electric field strength in the membraneu change
4. Using spin-labeled phospholipid molecules, the density gradient across the membrane thickness was established. Describe the experiment. Where is the viscosity higher: at the surface of the membrane or in its center
