7.
Contents 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Basic physical definitions ............................................ ............................................1 1 Atomic physics, electromagnetic waves, X‐ray ........... 2 Absorption, luminescence, lasers ............................... 3 Geometrical optics, microscopy, electron microscopy 4 Nuclear physics, radioactivity...................................... radioactivity ......................................5 5 Interaction of radiation with material, detection of radiation ...................................................................... ......................................................................6 6 Radiation biophysics, dosimetry, biological effect of radiations .................................................................... ....................................................................6 6 Experimental and diagnostic use of isotopes, accelerators, gamma camera CT, PET, SPECT.............. 7 Basic principles and applications of nuclear magnetic resonance (NMR). Electrospin resonance. .................. 7 Thermodynamics......................................................... Thermodynamics.........................................................9 9 Diffusion...................................................................... Diffusion ......................................................................9 9 Biological membranes and membrane transport ..... 10 Biophysics of the of the Sensory System ............................. 12 Sound, Ultrasound .................................................... ....................................................13 13 Information and entropy, communication systems, feedback.................................................................... feedback ....................................................................13 13 Modern microscopies, flow cytometry, sedimentation, electrophoresis (Medicine students only)................. only) ................. 14
1
Basic physical definitions
1.
Define kinetic energy in words and with a formula, and give its unit! Kinetic energy is the amount of work an object with a mass of m moving at a speed of v can can perform while its speed is reduced to zero: 1 2 Ekinetic mv 2 The unit of kinetic energy is joule.
8.
Define electron volt (eV)! Electron volt is a unit of energy. It is equivalent to the amount of kinetic energy gained by a single electron when accelerated through a voltage difference of 1 V.
3.
Define what force is! Force is a vector quantity characterizing the capability to cause acceleration.
4.
Define moment moment of inertia inertia in words words and with a formula! Moment of inertia (I ) serves the same purpose in circular motion as mass in linear motion. It characterized the resistance of an object against angular acceleration, i.e. the change in angular velocity. Moment of inertia of a point-like object can be calculated by the following equation: I mr 2 , where m is the mass of the object, r is the distance of the object from the axis of rotation.
10.
Define angular momentum! Angular momentum is analogous to momentum, it serves the same purpose in circular motion as momentum does in linear motion. By definition, the product of the angular velocity and the moment of inertia of an object is its angular momentum.
11.
Define the potential energy of of an object in a homogenous gravitational field! The potential energy of an object with mass m at a height of h in a homogenous gravitational field characterized by a gravitational acceleration of g is given by the following equation:
E pot
6.
mgh
Define the potential energy energy of a charged object in an electrostatic field! The electrostatic potential energy of an object with charge Q at position A in an electrostatic field is: E pot QU A ,where U A is the electric potential at point A.
13.
Define work work in words and with a formula! Work is the amount of energy transferred by a force. It can be calculated according to the follo wing formula: W Fs , where W is work, F is force and s is the displacement of the object in the direction of the force.
14.
Formulate the general form of of the work-energy work-energy theorem, and its special form for the electric and homogenous gravitational fields!
a
5.
Define momentum in words and with a formula! Momentum (p) is the product of the mass (m) and the velocity (v) of an object:
9.
Define acceleration in words and with a formula! Acceleration is the rate of velocity velocity change with time: dv , where a is acceleration, dv is the change in dt velocity in time t .
t
p mv
12. 2.
Define angular velocity in words words and and with with a formula! Angular velocity ( ) is the ratio of the angle ( , usually measured in radians) traversed to the amount of time (t ) it takes to traverse the angle:
Define Newton’s 2nd law in words and with a formula! The acceleration of an object (a) is given by the ratio of the net (or resultant) force acting upon it (Fn) and the mass of the object (m): F a n m
, m is the mass, v B and v A are the speed of the object at point A and B, respectively, W AB is the work done on the object between points A and B. In an electric field: Ekinetic, B E kinetic, A QU AB , Q is the
Define centripetal acceleration in words and with a formula! Centripetal acceleration (ac ) is the rate of change in the direction of velocity with time:
charge of the object, U AB is electric potential difference between points A and B In a homogenous gravitational field: h , is the height difference Ekinetic , B Ekinetic, A mghAB AB
ac
v
2
is velocity, r is is the radius of the 2 r , where v is
General form: E kinetic , B
E kinetic, A
between points A and B.
r path, is is angular velocity.
Minimum requirement questions, 2013/2014, page 1
1 2
m v 2B v 2A
W
AB
15.
Define power in words and with a formula, and give its unit! Power is the rate at which work is done, and it is calculated according to the following formula: P W , t where P is power, W is the amount of work perform in
time t . The unit of power is watt (W 16.
J
).
23.
What is the wavelength range of ultraviolet radiation? 10nm – 400nm 24.
What is the wavelength range of infrared radiation? 750nm – 1mm
25.
Define the limiting frequency (f max ) of braking radiation at an accelerating voltage of U. eU f max h where h is Planck's constant and e is the charge of an electron.
26.
What is the major difference between the photoeffect and the Compton effect? All of the energy of the X-ray (or gamma) photon is used to ionize the atom and set the electron in motion in photoelectric effect. On the contrary, only part of the photon energy is used for these processes in Compton effect, and the photon having lower energy is scattered.
27.
What is the minimal energy of a -photon needed for pair-production (not numerically)? The energy equivalent to the rest mass of an electron and a positron according to the Einstein mass-energy 2 equivalence equation: E=(me+mp)c , where me and m p are the rest masses of an electron and a positron, respectively, c is the speed of light in vacuum and E is the minimal energy of a -photon inducing pair production.
s
Define the term and unit of voltage! The voltage between points A and B is the difference between the electric potentials of points A and B. The unit of voltage is volt (V). If the voltage between points A and B is 1V (U B-U A=1V), the amount of work required to move a charge of 1 coulomb from point A to B is 1 joule.
17.
Define electric current and derive its unit from other SI units! Electric current is the amount of charge transported across a boundary per unit time. Its unit is ampere (A). coulomb A second
18.
Define resistance and give its unit! According to Ohm’s law resistance (R ) of a piece of conducting material is the ratio of the voltage applied across the piece of material (U ) and the current through the material (I ): U R I V ). The unit of resistance is ohm (
A Define what electric dipole is, and describe how to calculate its electric dipole moment! An electric dipole is a separated pair of -q -q positive charge (+q) and an equal amount of negative charge (-q). The electric dipole moment ( p) is defined by the following equation: p q r , where r is the separation distance between the
19.
charges. Electric dipole moment is a vector quantity pointing from the negative charge towards the positive one.
2 Atomic physics, electromagnetic waves, X‐ray 20.
h f c h ,
22.
29.
What is annihilation? The process in which an electron and a positron (or in general a particle-antiparticle pair) collide with each other and the total mass-energy of this particle system is converted to the energy of two gamma photons, is called annihilation.
30.
List
What is the difference between the orbital and spin angular momenta of an electron? - the orbital angular momentum originates from the orbital motion of an electron; its magnitude depends on the shape of the orbital and the interactions of the electron with the surrounding particles. - the spin angular momentum is an inherent property of the electron, its magnitude is independent of the surroundings. Align in ascending order the following components of the electromagnetic spectrum according to their energy: microwaves, gamma, ultraviolet, visible light, X-ray, infrared, radiowaves! radiowaves < microwaves < infrared < visible light < ultraviolet < X-ray, gamma
the
three
most
important
mechanisms
responsible for the absorption of and X-rays ! - photoelectric effect - Compton-effect - pair-production
where h and c are
Planck’s constant and the speed of light in vacuum, respectively, and is the wavelength of the photon. 21.
28. Why is a heavy nucleus necessary for pair- production? The presence of a heavy nucleus is required by the law of conservation of momentum.
Give the energy and momentum of a photon with frequency f. The energy of a photon with frequency f is hf , and its
momentum is
What is the definition of visible light? The range of electromagnetic radiation observable by the human eye (approximately 400-750 nm).
31.
Define interference! Interference is the superposition of waves that results in the generation of a new wave pattern.
32.
What is constructive and destructive interference? Interference is constructive when the amplitude of the resultant wave is greater than the amplitudes of the individual waves, and it is destructive when the amplitude of the resultant wave is less than that of the individual waves.
33.
What is the requirement for maximally constructive and maximally destructive interference if two propagating waves with identical wavelength interfere with each other? Maximally constructive interference takes place, if the path difference (s) between the waves is an integer multiple of the wavelength ( ): s l , where l=0,1,2,3…. This happens when the crest of one of the waves is superimposed on the crest of the other one.
Minimum requirement questions, 2013/2014, page 2
Maximally destructive interference is generated, if
1 s l , 2
c - concentration in mol/liter L - optical path length.
i.e. when the crest of one of the 44.
What does the molar extinction coefficient depend on? It depends on the type of the absorbing material, the wavelength of the light, temperature, the type of the solvent and the environment.
45.
How many fold does the intensity of light decreases if the absorbance (optical density, extinction) of a solution is 1? It decreases 10-fold.
46.
What is the definition of the molar extinction coefficient? It is the absorbance (optical density) of a solution with a concentration of 1M and an optical path length of 1 cm.
47.
At what wavelength are the characteristic absorption maxima of proteins and nucleic acids? proteins 280 nm, nucleic acids 260 nm
48.
What is monochromatic light? Light is monochromatic if its spectrum consists of a single wavelength only
Which amino absorption? Tyr, Trp, Phe
49.
What kind of special characteristics does laser light have? - monochromatic - coherence in time and d istance - small divergence - high light density.
What is the definition of a singlet and a triplet state? In a singlet and a triplet state the number of unpaired electrons is zero and two, respectively. In a singlet and a triplet state, the value of the resultant spin multiplicity is 1 and 3, respectively.
50.
What are the possible ways of relaxation of an excited electron in a molecule? (List at least 5 of them!) - vibrational relaxation - internal conversion - intersystem crossing - fluorescence - phosphorescence - delayed fluorescence - energy transfer to another molecule.
51.
What is the definition of fluorescence lifetime? The time during which the number of excited molecules decreases to 1/e-times (37 %) of its initial value.
52.
What is a., scintillation, b., chemiluminescence, c., photoluminescence? Processes where photon emission is elicited by a., ionizing radiation b., chemical reaction c., excitation by photons.
53.
How can fluorescence quantum efficiency (yield) be defined? The fraction of excited molecules emitting a fluorescent photon, or the number of fluorescence photons divided by the number of absorbed photons, or the rate constant of fluorescence divided by the rate constants of all possible deexcitation processes.
54.
Why is the fluorescence quantum yield always smaller than one? Because relaxation from the excited state can be accomplished not only by fluorescence emission.
55.
What is the lifetime range of fluorescence? = 10-9 – 10-7s
56.
What is the lifetime range of phosphorescence? = 10-6 – 10 s
waves is superimposed on the trough of the other one. 34.
Give the condition for constructive interference for an electromagnetic wave with wavelength diffracted on a crystal with a grating constant of c! o (angle of incidence is 90 ) c cos=l , where l=0,1,2,3,...n, =angle of diffraction How can the overdetermination of the Laue equations be resolved in the case of a three dimensional crystal? Either by rotating the crystal or making powder of it.
35.
What is the definition of transverse and longitudinal waves? In a transverse wave the displacement of oscillating particles is perpendicular to the direction of propagation of the wave. In a longitudinal wave the displacement is parallel to the direction of propagation.
3 Absorption, luminescence, lasers 36.
37.
38.
List the types of interactions laser light can have with tissues! photothermal (laserthermy, coagulation, vaporization, carbonization) fluorescence, photochemical reactions photodissociation multiphoton ionization
39.
When is electromagnetic radiation coherent? If it consists of photons capable of forming observable interference fringes.
40.
41.
What basic phenomena is the generation of laser emission based on? - population inversion is needed for light amplification to occur, and it is only possible in systems with 3 or more energy levels - stimulated emission is needed to give rise to coherent monochromatic light. What is the approximate coherence length of a laser and that of a classical light source? 10 10 cm and a couple of cm, respectively
42. Align in ascending order the following transitions according to their energy difference: vibrational, rotational and electronic! rotational < vibrational < electronic 43. Write the Lambert-Beer law and interpret the variables in the formula! J c L lg 0 cL A or J J 0 10 J J - intensity of light after passing through a material with thickness L J o- incident intensity of light when it enters the sample A – absorbance (optical density or extinction) - molar extinction coefficient
acids
Minimum requirement questions, 2013/2014, page 3
have
reasonably
high
57. Why is phosphorescence lifetime longer than fluorescence lifetime? Because phosphorescence is the result of spinforbidden transitions. 58.
59.
60.
What are the requirements of Förster-type resonance energy transfer? -the separation between the donor and the acceptor has to be in the range of 2-10 nm -there has to be an overlap between the emission spectrum of the donor and the excitation spectrum of the acceptor -the relative orientations of the donor and the acceptor have to be adequate.
What can Förster-type resonance energy transfer be used for in biology? For measuring inter- and intramolecular distances. What is photoselection? I t is the selection of an oriented subpopulation from a randomly oriented population of molecules by linearly polarized light.
62.
What is linearly polarized light? Light in which the electric vectors of all photons point in the same direction.
63.
List at least five parameters which can be determined using fluorescent measurements! - DNA, RNA, protein and lipid content of a cell, or the quantity of any kind of material that we tagged with a fluorescent label. - permeability of the cell membrane - intracellular enzyme activities - membrane potential - intracellular calcium level - intracellular pH - presence and density of cell surface antigens and receptors - mitochondrial potential and the number of mitochondria per cell.
4
Geometrical optics, microscopy, electron microscopy
64.
Define the index of refraction! The index of refraction (n) gives the speed of light (c ) in a given material according to the following equation:
c
c0
68.
What is numerical aperture? It is the product of the index of refraction of the material between the object and the objective (n), and the sine of the half angle of the objective (sin): n sin.
69.
Give the formula for the resolving power of a conventional light microscope! 1 2n sin f d
where: n = refractive index of the medium between the coverslip and the objective, = half angle of the objective, = wavelength of light, d = the minimum distance between two points at which they are resolvable. 70.
What is the function of the dichroic mirror in a fluorescence microscope? It reflects the excitation light, and is transparent for the emitted photons, therefore it separates the excitation and emission light paths.
71.
What is the function of the excitation filter in a fluorescence microscope? It is transparent only in the wavelength range in which the fluorescent dye can be excited, therefore it allows only those photons to reach the sample which can excite the fluorescent molecule.
72.
What is the function of the emission filter in a fluorescence microscope? It is transparent only in the wavelength range in which the fluorescent dye emits photons, therefore only the photons emitted by the fluorescent dye will reach the detector.
73.
List the imaging aberrations in optical systems! -chromatic aberration -spherical aberration -astigmatism -coma -curvature of the field of the image -barrel-shaped and cushion-shaped distortion of the image
74.
Give the equation for the relationship between the image distance (i), object distance (o) and the focal distance (f)!
, where c 0 is the speed of light in vacuum.
n
Write Snell’s law of refraction! A light beam is refracted when it travels from a material with a refractive index of n1 into a material with a refractive index of n2 (n2 n1). Refraction is described by the following equation:
sin sin
c1 c2
n2
, where and are the angles of
n1
incidence and refraction, respectively, c 1 and c 2 are the speeds of light in the two materials. 66.
How can the resolving power of a microscope be increased? -by decreasing the wavelength of light -by increasing the index of refraction of the material between the objective and the object -by increasing the half angle of the objective
Why is Förster type resonance energy transfer a sensitive method for distance measurements? Because its probability is proportional to the inverse sixth power of the separation between the donor and the acceptor.
61.
65.
67.
What is the shortest resolvable distance in a light microscope? approximately 200 nm
75.
1 1
1
i
f
o
Give the definition and SI unit of diopter! D (diopter)=1/f, is the refractive power of the lens, where f is the focal length of a given lens. SI unit: 1/m.
76. What were those two discoveries that made construction of an electron microscope possible? -an electron can be regarded as a wave, and its wavelength is only a fraction of the wavelength of visible light -an electron beam can be focused with a magnetic field 77.
List at least three signals that can be detected during an electron microscopic measurement! -back-scattered electrons
Minimum requirement questions, 2013/2014, page 4
-secondary electrons -characteristic X-rays -Auger electrons -absorbed electrons -cathode luminescence -transmitted electrons 78.
What are the two types of electron microscopes? transmission electron microscope (TEM) scanning electron microscope (SEM)
79.
What is the principle of transmission electron microscopy? A thin, typically 100 nm thick, sample is illuminated with an electron beam. The sample scatters a fraction of the electrons, i.e. the sample usually does not absorb the electrons. Using magnetic lenses an image is formed from the electrons going across the sample. The image is characteristic of the electron scattering properties of the sample.
80.
What is the principle of scanning electron microscopy? The sample is scanned by a thin electron beam. Secondary electrons induced by the electron beam are detected on a pixel-by-pixel basis.
5
Nuclear physics, radioactivity
81.
Give the definition of isotopes! Isotopes are the variants of a chemical element with a given atomic number whose mass numbers are different.
82.
84.
On what kind of energy level does a nucleon reside in a nucleus compared to the energy of a free particle? A bound nucleon has negative potential energy compared to a free particle.
88.
List the types of radioactive radiation and characterize the particles constituting them! Alpha radiation consists of helium nuclei. Negative beta radiation ( ) is composed of electrons, whereas + positive beta radiation ( ) consists of positrons. Gamma radiation is an electromagnetic radiation consisting of high energy photons.
89.
What is the direction of changes in the atomic number and the mass number of nuclei during alpha, both types of and gamma decay? change in mass change in atomic number number decay 4 2 + 1 (in decay and 0 electron capture), decay +1 (in decay) 0 0 decay
90.
Why is the spectrum of beta decay continuous? Besides an electron (or a positron) an antineutrino (or a neutrino) is also emitted, and the energy released during the decay is shared randomly between the two particles.
91.
What is electron capture and what does it produce? Some nuclei are capable of capturing an electron residing on the K shell decreasing their atomic number by one. The vacancy generated this way on the K shell is filled by an electron from a higher shell. This transition generates characteristic X-ray and/or an Auger electron.
List the isotopes of hydrogen with their mass number and the constituents of their nuclei!
Hydrogen Deuterium Tritium 83.
87.
Mass number 1 2 3
Composition 1 proton 1 proton+1 neutron 1 proton+2 neutron
What is the mass defect of nuclei? The mass defect equals the difference between the mass of a nucleus and the total mass of its constituents (Z: the number of protons and A-Z: the number of neutrons, where Z and A are the atomic number and the mass number of the nucleus, respectively): m = (Z mproton + [A-Z] mneutron) - matom where m is the mass defect, mproton, m neutron and matom are the masses of a free, unbound proton, a free, unbound neutron and the given atomic nucleus, respectively. What is the relationship between the total binding energy ( E) and the mass defect ( m) of a given nucleus? E=mc2, according to Einstein's mass-energy equivalence principle (c is the speed of light in vacuum).
85.
Describe how the binding energy per nucleon changes as a function of mass number. Binding energy per nucleon has a maximum at nuclei with mass numbers 55-60 (i.e. Fe).
86.
What are the properties of nuclear force (their range, strength and direction)? Nuclear forces have limited range, their effect is negligible at a distance of more than a single nucleon and they are independent of charge. They are very powerful attractive forces whose magnitude exceeds that of electrostatic forces.
92. Give the equation describing the number of undecayed nuclei as a function of time (i.e. the law of radioactive decay) .
N
N 0 e t
N0: number of radioactive nuclei at t=0, N: number of undecayed radioactive nuclei at the time of investigation, : decay constant, t: time. 93.
What is the physical meaning of the radioactive decay constant? Radioactive decay constant is equal to the inverse first power of the mean lifetime of a radioactive nucleus.
94.
What is the relationship between the radioactive decay constant ( ) and the half life (T)? ln 2 T ln 2: the natural logarithm of 2.
95.
Define biological half life. Biological half life is the time period during which half of the initial quantity of the radioactive isotope leaves the living system undecayed due to metabolism, secretion or excretion.
96.
Define effective half life. Effective half life gives the time during which the initial activity of a given type of radioactive nucleus decreases to half of its original value either by physical decay or metabolism. or alternatively
Minimum requirement questions, 2013/2014, page 5
Effective half life gives the time period during which the number of the udecayed nuclei decreases to half of the original value either by physical decay or biological processes. One of the definitions is enough to asnwer the question. 97.
Describe the relationship between the effective (T eff ), the physical (T phys ) and the biological (T biol ) half lives! 1 1 1
Teff 98.
Tphys
T biol
Describe the relationship between the physical ( phys ), the biological ( biol ) and the effective ( eff ) decay constants! eff = phys + biol
6
99.
Interaction of radiation with material, detection of radiation Write the formula describing the attenuation of gamma or X-ray radiation in an absorbing material.
J
J 0 e x
where J 0 denotes the incident intensity and J is the transmitted intensity after passing through an absorber of thickness x . µ is the absorption/attenuation coefficient. 100. What is the definition of the attenuation coefficient of a material for gamma or X-ray and what is its SI unit? The attenuation coefficient is the reciprocal of the distance at which the intensity of the radiation decreases to 1/e-times (37%) of the initial value. [µ]=1/m. 101. How does the intensity of -radiation change as a function of the distance from the radiation source? It is constant in the beginning then suddenly decreases to zero. 102. What is responsible for the energy loss of an alpha particle along its path? Ionization. 103. What kind of radioactive radiations can be detected by a GM-counter? -, - and -particles can be detected. 104. What is the basic principle of operation of a photomultiplier tube? Electrons liberated from a light sensitive cathode by photons are accelerated in an electric field and collide into other electrodes (dynodes) whose potentials are increased in succession along the length of the tube. The energy of this collision is sufficient to free several secondary electrons. In this way the number of electrons increases at each dynode. 105. What is the basic operation principle of ionization detectors? Electrons and positive ions produced by the ionization process are separated by the electric field of the detector. The charged particles are attracted towards the appropriate electrodes and generate electric impulses. 106. What is the principle of detection of radioactive radiation by a scintillation detector?
In certain organic and inorganic substances the energy of radioactive particles is converted to luminous energy, i.e. they generate visible light flashes. 107. List the radioactive radiations in order of increasing penetrability! <<
7
Radiation biophysics, dosimetry, biological effect of radiations
108. What is the biological effect of radioactive radiation based on? Excitation and ionization of atoms and/or molecules of living systems. 109. What kind of particles are able to produce a biological effect in radiation biology? Particles giving their energy partially or totally to the biological object are able to produce a biological effect. 110. What is a hit in radiation biology? If one or more ionizations are produced in the radiosensitive volume of a biological object. 111. How can a dose-response curve be constructed? The applied radiation dose is plotted on the horizontal axis and the ratio of the surviving organisms (N) and the total number of organisms before irradiation (N0) is plotted on the vertical axis. 112. What is the probability of generating exactly ‘n’ hits when applying a dose of D in volume V?
Pn
VD n!
n
e
VD
113. How does the number of ionizations depend on the dose of the radiation? The number of ionizations is linearly proportional to the dose. 114. Write the equation describing the dose-response curve when one hit is necessary for inactivation? N N 0
e VD
where N is the number of surviving organisms, No is the total number of organisms, D is the dose and V is the radiosensitive volume. 115. What is D37 ? D37 denotes the dose at which 37 % of the irradiated objects survive. If one ionization causes inactivation, D37 corresponds to one hit in a radiosensitive volume (VD=1, that is D=1/V). 116. What is the principle of the indirect action of radiation? In aqueous solutions a particle of an ionizing radiation most probably causes ionization of the solvent (water) because water molecules outnumber solute molecules. Radicals generated by the above process are responsible for damaging solute molecules. This way the target “gets bigger”. 117. What kind of products are capable of damaging biological objects arise during irradiation of aqueous solutions? – hydrated e , H, OH, H2O2
Minimum requirement questions, 2013/2014, page 6
118. What is the definition of absorbed dose? Absorbed dose, Da, is defined for any ionizing radiation as the ratio of radiation energy converted into ionization energy and the mass taking up the ionization energy. Unit: Gray (Gy), 1 Gy= 1J/kg
128. How and why does fractionation of radioactive radiation influence the radiosensitivity of cells? Fractionation decreases the radiosensitivity of cells, because radiation-induced damage can be partly repaired between exposures to the radiation.
119. What is the definition and unit of KERMA (kinetic energy released in material)? KERMA is the sum of the initial kinetic energy of all particles generated by the ionizing radiation in an absorbing material divided by the mass of the absorbing material. Unit: Gray (Gy), 1 Gy= 1J/kg
8
120. What is the definition and unit of exposure in the case of X-ray and -radiation? Exposure is defined as the ratio of the sum of positive (or negative) charges produced by ionization in a volume element and the mass of this element if every charged particle loses its kinetic energy in air. Its unit: Coulomb/kg. 121. Define the unit of equivalent dose! Its unit is 1 Sievert (Sv). 1 Sv is the dose of any ionizing radiation which produces the same effect on human beings as 1 Gy absorbed dose of conventional X-ray. Conventional X-ray consists of 250 keV photons. 122. List the physical factors influencing radiation sensitivity! The quality of radiation (it influences radiation sensitivity through ionization density and penetrability), time factor, temperature, effect of oxygen, substances protecting from radiation. 123. What is the smallest dose which can produce a biological effect? Theoretically even a single quantum is enough to produce a point mutation, since any photon that is able to produce ionization is capable of breaking a chemical bond. 124. How can radioactive radiation cause a double strand break in DNA? A double strand break of DNA can be caused by a single ionization event or as a result of simultaneous single strand breaks on the opposite strands of DNA helix which are produced by ionizations originating from separate events. 125. Write the equation describing cell according to the linear-quadratic model.
S ( D)
N N 0
survival
D D e 2
Where S(D) is the survival fraction as a function of dose D, and α and β are tissue and radiation dependent constants. Parameters and are proportional to the probability of "one-step" and “two-step” DNA double strand breaks, respectively. 126. In which part of the cell cycle are cells the most and the least sensitive to radioactive radiation? Generally, the majority of cells are considered to be the most radiosensitive during mitosis and most resistant in late S phase. 127. How does radiosensitivity changes as a function of the level of oxygenation? The well-oxygenated cells have greater radiosensitivity than hypoxic cells, because in the presence of oxygen there is higher chance to produce radicals.
Experimental and diagnostic use of isotopes, accelerators, gamma camera CT, PET, SPECT
129. List the most important types of applications of radioactive isotopes in medical diagnosis! in vitro laboratory tests determination of the volume of body compartments two- or three-dimensional imaging of the distribution of radioactive isotopes in the body 130. What is the operation principle of a -camera? A substance labeled with a radioactive isotope is injected into the body (radiopharmacon). The emitted photon passes through a collimator and collides into a scintillation detector. The distribution of the radiation source can be mapped by the counts of photomultiplier tubes connected to the detector. 131. What is the principle of SPECT? Images are taken from different directions by a camera. The three-dimensional distribution of the radiation source is calculated from these images. 132. What kind of isotopes can be used in PET? Only nuclei with positive -decay can be used 133. What is the principle of determination of the location of a radioactive isotope in PET? A positron is generated in a positive beta decay. It collides with an electron in a distance shorter than 1 mm from its generation and the two particles are annihillated. Two gamma photons generated in the annihillation reaction leave the place of annihillation in opposite directions. A circular array of detectors senses these gamma photons. If two detectors opposing each other signal at the same time (coincidence), annihillation took place along the line connecting the two detectors. The intersection of many such lines gives the exact location of the radioactive source. 134. What is the principle of computer tomography? X-ray images are taken of the human body from different directions. The X-ray absorption capacity of volume units (voxels) of the body can be calculated from these images. 135. In which respect does a CT image provide more information than a conventional X-ray image? A conventional X-ray image contains only the two dimensional projection of the distribution of the X-ray absorbing material, while a CT image also reveals the third dimension (depth) of the object.
9
Basic principles and applications of nuclear magnetic resonance (NMR). Electrospin resonance.
136. Which nuclei are able to give an NMR signal? Whose resultant nuclear spin is different from zero; i.e. those nuclei which contain odd number of protons and/or odd number of neutrons.
Minimum requirement questions, 2013/2014, page 7
137. List at least three nuclei which can be used in biological applications of nuclear magnetic resonance! 1 2 13 14 19 31 H, H, C, N, F, P
proton is about 2000 times greater than that of an electron, the Bohr magneton and, as a consequence, the energy difference between the two states will be much higher in ESR.
138. What happens to the elementary magnetic moments in an external magnetic field? The interaction of magnetic moments with the external magnetic field causes their alignment as well as their precession about the magnetic field.
146. What factors influence the resonance frequency in NMR? Quality of the absorbing nucleus, its chemical environment and the strength of the external magnetic field.
139. What are the possible states of the magnetic 1 moment of a H nucleus in an external magnetic field? 1 The nuclear spin of H is ½, therefore its magnetic moment has two possible alignments with respect to the magnetic field: it can be aligned either with (parallel alignment – lower energy level or ground state) or against (antiparallel alignment – higher energy level or excited state) the magnetic field.
147. How can the relative concentration of absorbing nuclei be determined from an NMR spectrum? From the area under the absorption lines corresponding to different nuclei.
140. What is the condition for resonance absorption in NMR?
E2 E1 hf
gN N B N B
E 2 - E 1: the energy difference between the excited and ground states of the nuclear spin B: magnetic field h: Planck's constant f: frequency of the applied electromagnetic radiation g N: nuclear g-factor; γN: gyromagnetic ratio μ N: nuclear magneton 141. Define the gyromagnetic ratio of a nucleus! It is the ratio of the magnetic moment (MN) to the intrinsic angular momentum (spin; LN) of the given nucleus: g N M N LN N N
g N is the nuclear g-factor, μ N is the nuclear magneton
and
h 2 (h is the Planck constant).
142. What region of the electromagnetic spectrum can be used to excite nuclear and electron spins placed in a magnetic field? 8 Radiowaves ( 10 Hz): NMR 10 Microwaves ( 10 Hz): ESR 143. What is the Bohr magneton? It is a physical constant and the natural unit for expressing the magnetic moment of an electron. B
e
2me
e: elementary charge, me: mass of the electron
= h/(2) (h is Planck's constant). 144. What is the nuclear magneton? It is a physical constant and the natural unit for expressing magnetic dipole moments of heavy particles (e.g. nucleons, atomic nuclei). N
e
2m p
,
e: elementary charge, m p: mass of the proton
= h/(2) (h is Planck's constant). 145. Why are the resonance frequencies applied in ESR much higher than those used in NMR in a given magnetic field? The energy difference between the ground and excited states is linearly proportional to the Bohr (ESR) or the nuclear magneton (NMR). Since the rest mass of a
148. What is chemical shift in NMR? The local magnetic field experienced by a given nucleus is altered by the chemical environment resulting in a change in its original resonance frequency. 149. What is the equilibrium occupancy of the two states 1 of H nuclei in a magnetic field? The occupancies of the two states are determined by the Boltzmann distribution. The lower energy level (parallel alignment) contains slightly more nuclei than the higher level (antiparallel alignment). 150. What is the macroscopic consequence of the alignment of nuclear magnetic moments by the external magnetic field? A macroscopic magnetization (equilibrium or longitudinal magnetization) is formed in the direction of the external magnetic field. 151. What provides the signal in pulse NMR techniques? The precession of transverse magnetization (i.e. the xy component of the net magnetization vector at right angles to the main magnetic field) generated by a short, intense radiofrequency pulse. Precession takes place at the resonance frequency of the nucleus in the given magnetic field. 152. What is spin-spin and spin-lattice relaxation? Spin–spin relaxation is the mechanism responsible for the decay of transverse magnetization generated by the radiofrequency pulse. Spin–lattice relaxation is responsible for the recovery of the original longitudinal magnetization vector. 153. What kind of parameters does an MRI image reveal? 1 About the density of H nuclei in a volume unit (voxel) and about their spin-spin and spin-lattice relaxation rates. 154. How is the signal localized in MRI? In addition to the basic static magnetic field (B0) linear magnetic field gradients are applied in different directions. Since the resonance frequency is linearly proportional to the magnetic field experienced by the nucleus, location of the signal can be encoded on the basis of the frequency. 155. What is in vivo magnetic resonance spectroscopy (in vivo MRS)? It is a non-invasive, analytical technique that can be used to study metabolic processes in the volume of interest of a living organism on the basis of characteristic NMR spectra of the respective metabolites.
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10 Thermodynamics 156. What is an isolated system in thermodynamics? A system is isolated if it doesn't exchange either energy or material with its environment. 157. What is a closed system in thermodynamics? A system is closed when it can exchange energy, but no material with its environment. 158. What is an adiabatic transition? The transition where no exchange of heat occurs, is called adiabatic. 159. Define heat and give its unit! Heat is energy transferred from one body to another due to difference in their temperatures. The unit of heat is the same as that of energy, i.e. joule. 160. The number of particles residing on energy levels with energies E 1 and E 2 is N 1 and N 2, respectively. Give the Boltzmann distribution describing the relationship between N 1 and N 2! E E 2 1 N2 N1e kT , where k is Boltzmann’s
constant, T is the absolute temperature. 161. What kind of quantities are called extensive? A physical parameter, which depends on the size of the system, is called extensive. Such a parameter is additive, i.e. its values are added for different parts of a system. 162. What kind of quantities are called intensive? Physical parameters whose value does not depend on the size of the system are called intensive quantities. Intensive quantities are not additive, they tend towards spatial equilibrium. 163. Define what internal energy is! The total energy related to the structure and internal properties of an object arising from the random motion of and forces acting between atoms and molecules of the system is called internal energy. 164. Write the equation relating the internal energy of monoatomic ideal gas to temperature!
Einternal
3 2
NkT , where E internal is the internal energy, N
is the number of atoms, k is Boltzmann’s constant and T is the absolute temperature. 165. What is the entropy of a chemically pure, solid crystal at absolute zero temperature ? S=0 166. Is chemical potential an extensive or an intensive quantity? It is an intensive quantity. 167. Two bodies are in thermodynamic equilibrium (T 1=T 2 ). Can exchange of energy occur between them? Yes, but the average amount of energy transmitted by the bodies to each other is equal. 168. Is a living organism an isolated, closed or open thermodynamic system? Open.
169. Is the second law of thermodynamics valid for a living system, and how can it be applied? Yes, but it can be applied only if the living system and the surrounding environment together are treated as an isolated system. 170. When is a mixture in thermodynamic equilibrium? If the chemical potential of all of its components is the same at each point of the system. 171. What is the definition of chemical potential? Chemical potential of a substance is the Gibbs free energy of one mole of the given substance, i.e. the chemical potential of a substance gives by how much the Gibbs free energy of a thermodynamic system increases when one mole of the given substance is added to the system (at constant temperature and pressure). 172. What is the classical thermodynamic definition of entropy? Q S rev T S: entropy change, Qrev: heat taken up reversibily, T: absolute temperature 173. Define the relationship between entropy and thermodynamic probability! S k ln S: entropy, k: Boltzmann constant, Ω: thermodynamic probability 174. Define thermodynamic probability! Thermodynamic probability of a macrostate is the number of microstates associated with the macrostate. 175. What is the range of values of thermodynamic probability ( Ω )? 1 . 176. What is the range of values of mathematical probability (P)? 0 P 1. 177. Which state functions determine the direction of a chemical reaction in an isobaric-isothermal (p=constant, T=constant)? Give the definition of the function! Gibbs free energy, G=H-TS where H is the enthalpy, T is the absolute temperature and S is the entropy of the system.
11 Diffusion 178. Define the frictional force (F f ) acting on a molecule with velocity v in an aqueous environment F f =-fv, where f is the form factor. 179. What is the relationship between the absolute temperature (T) and the average kinetic energy of a molecule (E kin ) in a system containing monatomic gas in thermal equilibrium? 3 Ekin kT 2 where k is the Boltzmann constant. 180. What is diffusion? Net flow of material propelled by Brownian motion due to a gradient of the chemical potential.
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181. What is the physical meaning of the diffusion constant? The diffusion constant (D) is the amount of material transported through unit surface area in unit time at a unit concentration gradient. It characterizes the mobility of molecules. 182. What is the unit of diffusion constant? 2 [D] = m /s 183. Give the average squared displacement particle with diffusion constant D!
of a
x 2 2 Dt where t is time, and displacement.
x 2 is the average squared
184. Write Fick's first law and interpret the constants and physical quantities! c I v DA x I v is the quantity of material transported through the surface A per unit time by a concentration gradient ∆c/ ∆ x , D is the diffusion constant 185. How does the diffusion constant (D) depend on temperature (T) and the radius (r) of a spherical molecule? T D r 186. Write down the equation describing the relationship between the diffusion constant (D) and the form factor (f)! kT D f
where k is the Boltzmann constant and T is the absolute temperature. 187. Which parameters tend toward spatial equilibrium during a diffusion process? The chemical potentials of the components.
188. Write down van't Hoff's law!
= posmosis = cRT, where = posmosis - osmotic pressure, R is the universal gas constant, T is absolute temperature, c is the molar concentration of the material in solution. 189. What is osmosis? Flow of the solvent to a concentrated solution from the more dilute one, if the two compartments are separated by a semipermeable membrane. This material flow decreases the concentration gradient between the two solutions. 190. What is the osmotic pressure? It is the pressure, which is able to prevent the solvent flow from the pure solvent to the solution through the semipermeable membrane 191. Write the continuity equation for fluid flow!
A1v1
A2v2
where A1 and A2 are the cross sectional areas of the tube, v1 and v2 are the average velocity of the fluid at cross sections A1 and A2, respectively. 192. Describe in words the meaning of the continuity equation! In the case of incompressible fluids the volumetric flow rate is uniform along the entire tube.
193. Describe in words the law of Bernoulli! The sum of the statical, dynamic and gravitational (hydrostatic) pressures is constant
12 Biological membranes and membrane transport 194. What is the permeability constant? The permeability constant is the amount of material transported through the membrane per unit surface in unit time due to unit concentration difference. 195. Give the equation describing the flux of material transported across a membrane due to concentration difference between two compartments separated by the membrane!
J m
p c
Jm – is the flux of the material, which is the amount of material transported through a unit membrane area in a 2 unit time Unit: mol/(m s) p – membrane permeability constant, (m/s) c – concentration difference between the concentrations on the two sides of the membrane 196. What does it mean that lipids are amphipathic molecules? They consist of hydrophobic and hydrophyilic parts. 197. What are the possible forms of motion of a lipid molecule in a membrane? -lateral diffusion -rotational diffusion -transmembrane flip-flop -flexible motion of fatty acid side chains. 198. What are the possible phase states of biological membranes? -gel phase -liquid crystal/ fluid phase 199. What changes in the properties of the fatty acid side chains increase the transition temperature of a membrane? -increase in the saturation of fatty acid carbon-carbon bonds -increase in the length of the fatty acid side chains 200. How does cholesterol change the fluidity of lipid membranes? Below the phase transition temperature it usually increases, above the phase transition temperature it decreases. 201. What is the magnitude of the lateral diffusion constant of lipids and proteins in biological membranes? -8 -9 2 lipids: 10 -10 cm /s -9 -12 2 proteins: 10 -10 cm /s. 202. Which methods can be used to measure the lateral diffusion of proteins in biological membranes? - Fluorescence Recovery After Photobleaching (FRAP) - Single Particle Tracking (SPT) - Fluorescence Correlation Spectroscopy (FCS) 203. For what kind of molecules is the permeability of biological membranes the highest? For small, uncharged, apolar molecules, e.g. O2, N2. 204. How can membrane proteins be classified based on their function? transport and channel proteins receptor and signal transducing proteins
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-
enzymes structural membrane proteins.
217. Write the Nernst equation! U 0, x
205. What are the extra- and intracellular concentrations + + 2+ of Na , K and Ca ions? extracell. intracell + Na 140 mM 10-20 mM + K 5 mM 140-150 mM
Ca
+
1-2 mM
-
10 mM
206. What is passive transport? Transport processes driven by the electrochemical potential gradient which do not need active metabolism are called passive transport. 207. What is active transport? Transport processes that results in material flow against the electrochemical potential gradient at the expense of energy utilization are called active transport. 208. What is primary active transport? The transporter pumps ions/molecules across the membrane against their electrochemical gradient using energy from ATP hydrolysis. 209. What is secondary active transport? Secondary active transport moves ions/molecules across the membrane against their gradient using energy stored in the gradient of another ion, created by a primary active transport mechanism. 210. What is simple diffusion across biological membranes? The passive transport of small and lipid-soluble molecules across the membrane. 211. What is facilitated diffusion? The passive transport of membrane impermeant ions/molecules across the membrane aided by transport proteins (ion channels or carriers) molecules. 212. What are the properties of facilitated or carrier- mediated diffusion? -transporter proteins specifically bind the transported molecules -the transport can be selectively inhibited -the flux of transport can be saturated over a given concentration of the transported material. 213. What kind of ion channels do you know based on their mode of activation? -ligand gated ion channels -voltage gated ion channels -second messenger gated ion channels -mechanical deformation (stretch) activated ion channels. 214. What is the function of ionophores? They promote the selective transport of ions through lipid membranes. 215. How can ionophores be grouped according to the mechanism of ion transport? - carrier ionophores - channel forming ionophores 216. List the factors contributing to the maintenance of quiescent membrane potential! - diffusion potential - Donnan potential - active transport by ion pumps.
E x
RT z x F
ln
x i x o
where U0,x (or Ex) is the equilibrium potential of the given ion, R is the universal gas constant T is the absolute temperature zx is the charge of the given ion F is the Faraday constant [x]e and [x]i are the extra- and intracellular concentrations of the given ion, respectively. 218. What is the equilibrium potential of an ion? The membrane potential where the net flux of the given ion is zero, i.e. the system is in thermodynamic equilibrium for the given ion. 219. Are the ions on the two sides of the membrane of a living cell in thermodynamic equilibrium? Why? No. There is no thermodynamic equilibrium because the net passive flux of a given ion is not zero at the resting membrane potential. 220. Describe the relationship between net fluxes of major permeating ions at the resting membrane potential! JNa+JK+JCl=0, where Jx is the flux of ion x. 221. Give the definition and unit of flux! Flux (J) is the amount of transported items across unit 2 cross section area per unit time. Unit: mol/(m s) 222. Give the Goldmann-Hodgkin-Katz equation!
Um
E m
RT Fz
ln
pK K pCl Cl ... i i o p Na Na pK K pCl Cl ...
p Na Na
o
o
i
Um (Em) is the resting membrane potential (diffusion potential); R is the universal gas constant; T is the absolute temperature; F is the Faraday constant; [x]0 and [x]i are the extra- and intracellular concentrations of ion x, respectively; px is the permeability of the cell membrane for ion x. 223. Give the definition and unit of conductivity! G (conductivity)=1/R (where R is the resistance) Unit: 1/ =siemens (S). 224. Give the current carried by ion x through the cell membrane if the membrane potential is E m!
I x
Gx En Gx E m E x
where Ix is the current; Gx is the conductivity of the membrane for ion x (G=1/R); Ex is the equilibrium potential of ion x. 225. Define the action potential and interpret the ionic basis of its generation. The action potential is a characteristic, time-dependent change in the membrane potential as a result of timeand membrane potential-dependent changes in the ion permeabilities of the membrane. In the depolarization + phase the Na permeability is dominant, the subsequent repolarization is the result of a concurrent + + decrease in Na permeability and an increase in K permeability. 226. What is the principle of voltage-clamp? The membrane potential is held at a controlled value independently of ion currents through the membrane.
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227. List the methods that can be used for measuring the membrane potential of living cells! -optical methods with membrane potential sensitive dyes; -electrophysiological methods (microelectrode, currentclamp) 228. What kind of currents can be measured by patch- clamp? -single channel currents (eg. cell-attached configuration) -ion currents flowing through the entire membrane of the cell (whole-cell configuration). 229. What are the most important features of ion channels? -selective permeability: the channel is permeable only to a certain ion species; -gating: appropriate trigger/signal/event causes a conformational change in the channel protein resulting in the transition among different states (closed, open, inactivated) of the channels 230. What is the range of the voltages corresponding to the R waves of an ECG? millivolts 231. Give the Einthoven-Waller rule and interpret the variables in the formula! R1 + R3 = R 2, where R1, R2 és R 3 are the projections of the integral vector on the sides of the Einthoven triangle. 232. What is the meaning of an ECG curve in the case of unipolar and bipolar leads? Unipolar: It is the potential difference between an exploring and a reference electrode. Bipolar: It is the potential difference between two exploring electrodes.
13 Biophysics of the Sensory System 233. Which physical characteristics of the eye lens are changed during accommodation? The shape (radius of curvature) and the refractive index of the lens. In the case of humans the former is the dominant. 234. What is the resolution of an eye? The smallest visual angle at which the images of two points can be distinguished. 235. What is the physical and biological limit of the resolution of an eye? Physical: The separation between the two points to be distinguished should not be less than the wavelength of the illuminating light. Biological: Images of the two points to be distinguished have to be on different photoreceptors, and there has to be an unstimulated receptor between them. 236. What does it mean that photons are only triggers for photoreceptors? The energy of photons is used by the receptors for inducing chemical (signal transducing) processes. 237. Which receptor cells of the retina are responsible for color vision and vision under dim conditions! color vision: cones; vision under dim conditions: rods. 238. What is the principle of Young-Helmholtz theory? The physiological basis of color vision is the existence of three different color sensitive receptors (the cones)
with different photopigments which are able to make a distinction between red, green and blu e colors. 239. What is ERG? Electroretinogram: it records the potential changes of the retina as a whole during stimulation with light. 240. What is the threshold intensity of hearing? Specify its value! Threshold intensity of hearing is the minimal intensity of the 1000 Hz sinusoidal sound audible by a normal -12 2 human ear. Its value is about 10 Watt/m . 241. How does the intensity of sensation (loudness) changes as a function of the intensity of the stimulus? Sensation is proportional to the logarithm of the relative intensity of the stimulus. 242. What is the advantage of the phon scale compared to the bel (decibel) scale? When using the phon scale the intensities of both the reference and actual sound intensities are converted to the intensities of the corresponding 1000 Hz sound, i.e. the reference is the threshold intensity of the 1000 Hz -12 2 sound (10 Watt/m ), the actual intensity is the intensity of the 1000 Hz sound inducing the same sensation of loudness as the sound under investigation. Therefore, the threshold of hearing is 0 phon for every frequency. 243. Give the Weber-Fechner law! actual stimulus intensity sensation const lg reference stimulus intensity 244. A sound with intensity J and frequency of 2000 Hz is produced by a sound generator. What is the loudness according to the phon scale? J H phon 10 lg 1000 (phon) J 0
where Hphon is the loudness in phons; J1000 is the intensity of the sound with a frequency of 1000 Hz causing the same sensation of loudness as the sound with a frequency of 2000 Hz with intensity J; J0 is the threshold intensity of hearing for the 1000 Hz -12 2 sound (10 Watt/m ). 245. What kind of relationship is represented by the isophonic curves? The sound intensities producing the same sensation of loudness are plotted against the sound frequency. 246. Give the threshold values of hearing according to the phon scale for sounds whose frequencies are 1000 Hz and 2000 Hz, respectively! 0 phon, the threshold of hearing is the same (0 phon) for any frequency. 247. What is the basis of the sone scale? Sensation can be more precisely described by the power of the relative stimulus intensity with a fractional exponent.
J H sone 16 J 0 1
0.3
where Hsone is the loudness in sone, and J and J0 are the stimulus intensity in question and the reference stimulus intensity, respectively. 248. What is the mechanism of hearing by conduction (also called ossicular conduction)?
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air
The vibration reaches the inner ear through the auditory meatuses and the system of the tympanic membrane and auditory ossicles. 249. What is the mechanism of hearing by bone conduction? The vibration reaches the inner ear directly through the cranial bones.
A part of a ultrasound beam is reflected at the interfaces of different tissues with different acoustic impedance, so the boundaries of different tissues can be mapped using the intensity and the delay of the echo compared to the impulse leaving the transducer.
15 Information and entropy, communication systems, feedback
250. What are the physical principles giving rise to an increased pressure on the foot plate of the stapes compared to the pressure of the original sound? 1. the cross-sectional area of the ear drum is much larger than that of the stapes foot plate; 2. lever-like functioning of auditory ossicles.
262. What is the advantage of a redundant code system compared to a nonredundant one? It decreases distortion of the coded information during transmission via the channel.
14 Sound, Ultrasound
263. What is the basic unit of information? Bit (binary unit or basic unit).
251. Give the frequency range of sound waves audible by a normal human ear! 20 Hz - 20000 Hz. 252. What is ultrasound? Sounds whose frequency is between 20000 Hz and 10 10 Hz. 253. What is infrasound? Sound with a frequency less than 20 Hz. 254. Give the definition and unit of sound intensity! The energy carried by the sound wave perpendicularly through unit cross-sectional area per unit time. Its unit 2 is Watt/m . 255. What does the velocity of sound depend on? The velocity of sound depends on the properties of the medium (density and compressibility). 256. What does acoustic impedance depend on? Acoustic impedance (Z) is linearly proportional to the density of the medium () and the velocity of the ultrasound (c). Z=c. 257. List the most widespread effects suitable for the generation of ultrasound! - inverse piezoelectric effect - electrostriction effect - magnetostriction effect 258. Describe the relationship between the amplitude of the ultrasound-induced pressure fluctuation ( ∆P max ) and the intensity of ultrasound (J)! ∆Pmax
264. Give the definition of bit! The information content corresponding to choosing one of two, equally possible outcomes of an experiment is 1 bit. 265. How can the accuracy of the information transmission be guaranteed in a noisy environment? Increasing the redundancy. 266. What is the task of the coder in an information chain? Converting the information generated by the source into appropriate form for transmission, processing and storage. 267. Where does most of the noise affect information in a communication system? In the channel, between the transmitter and the receiver. 268. What is feed-back? A part of effect produced by the system conducted back to the controller to check the desired effect. 269. Which numerical system do the nucleotide triplets belong to and why? To quaternary numerical system because there are f our types of bases in DNA. 270. How many digits does a word have to contain to be able to code the primary structure (amino acid sequence) of proteins in DNA? Three. 271. Write down the equation describing redundancy and interpret the variables!
2
where Z is acoustic impedance. 259. What is cavitation? Attractive forces between fluid particles may be overcome by the alternating pressure changes induced by ultrasound and microscopic cavities containing no fluid particles may be generated. 260. How does the intensity of ultrasound change while it passes through a certain medium?
where J0 is the intensity of the ultrasound entering the medium, µ is the absorption coefficient and x is the thickness of the medium.
R
H max
H
H max
R: redundancy, Hmax is the theoretically attainable maximal information content of a coded message based on the given set of signs, H is the actual information content. 272. Can redundancy be 0% or 100%? 0 % - yes; 100 % - no. 273. Write the Shannon-equation describing information content of an experiment! k
U
pi log pi i 1
261. What is the basis of imaging with ultrasound?
Minimum requirement questions, 2013/2014, page 13
the
where U is the uncertainty of the experiment and pi is the probability of a given outcome. 274. What is relationship between the uncertainty and the number of possible outcomes of an event? Logarithmic. 275. What is an algorithm? The collection of rules directing the operation of an automat. 276. Define the set of characters for a coding system! The complete set of coding elements in a coding system (e.g. letters in the English alphabet), or it is the collection of all possible outcomes of an experiment 3 (e.g. for DNA triplets it is the collection of 4 =64 possible base orders). 277. Define the information content of a message or an experiment in which any character or outcome is equally possible! It is logarithm with base two of number of all possible outcomes of the experiment; or another way: the number of yes or no questions by which the outcome of the experiment can be figured out.
16 Modern microscopies, flow cytometry, sedimentation, electrophoresis (Medicine students only) 278. What is the operating principle of a confocal laser scanning microscope? A pinhole with a small diameter blocks the way of light beams originating from out of focal planes. This way the image of the object will be sharp. The whole process is extended to the whole plane by scanning.
284. Define the sedimentation constant and give its unit! The sedimentation constant is the sedimentation velocity of a molecule gained by unit acceleration, that is the sedimentation velocity divided by the centripetal -13 acceleration. Unit: 1 Svedberg (S)=10 sec 285. How can the density of an unknown macromolecule be determined by sedimentation experiments? Macromolecules centrifuged in a density gradient (e.g. cesium chloride) stop sedimenting in the layer whose density is identical to their own. 286. How does the sedimentation equilibrium depend on the form factor in the case of sedimentation equilibrium method and why? It is independent because after reaching the equilibrium molecules stop moving. 287. What is electrophoretic mobility? Electrophoretic mobility is the velocity generated by unit electric field strength. 288. List the factors influencing the electrophoretic mobility of a macromolecule! - molecular mass - net charge, - pH of the medium - form factor. 289. What is the principle of isoelectric focusing? In pH gradient during electrophoresis each compound migrates towards the location, where pH is equal to that of its isoelectric point and net charge of particle becomes zero stopping of further migration.
279. Which microscope based on visible light could surpass the theoretical limit of resolution dictated by the Abbe equation? Near-field microscopy. 280. What is the principle of atomic force microscopy? A silicium tip hovers 5 nm above the surface because it cannot get any closer due to electrical repulsion and the weak spring constant of the suspension. In this way the tip is able to scan the surface of the object and detect the height differences at each point. 281. What is the resolution microscopy? Angström (0.1 nm)
limit of
atomic force
282. What are the advantages of flow cytometry and cell sorting compared to spectrofluorimetric measurements? 1 - more information can be obtained separately about individual cells at the same time 2 - numerous cells can be studied within a short time 3 - homogeneity or heterogeneity of a cell population can be revealed 4 - cells can be separated on the basis of their size and other characteristics that can be labeled fluorescently 283. List forces and their directions acting on a molecule sedimenting in a centrifuge tube! Centrifugal force pointing away from the axis of rotation whereas both frictional force and buoyant force pointing towards the axis of rotation.
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