Biophysics Flashcards

Vocabulary flashcards for biophysics review.

Kinetic Energy

The amount of work an object with a mass of m moving at a speed of v can perform while its speed is reduced to zero; unit is joule.

Electron Volt (eV)

A unit of energy equivalent to the kinetic energy gained by a single electron when accelerated through a voltage difference of 1 V.

Force

A vector quantity characterizing the capability to cause acceleration.

Acceleration

The rate of velocity change with time.

Newton's 2nd Law

The acceleration of an object (a) is given by the ratio of the net force acting upon it (Fn) and the mass of the object (m).

Centripetal Acceleration

The rate of change in the direction of velocity with time.

Angular Velocity

The ratio of the angle traversed to the amount of time it takes to traverse the angle.

Momentum

The product of the mass (m) and the velocity (v) of an object.

Moment of Inertia

Serves the same purpose in circular motion as mass in linear motion; characterizes the resistance of an object against angular acceleration.

Angular Momentum

Analogous to momentum; serves the same purpose in circular motion as momentum does in linear motion.

Potential Energy in 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.

Potential Energy in Electrostatic Field

The electrostatic potential energy of an object with charge Q at position A in an electrostatic field.

Work

The amount of energy transferred by a force.

Buoyant Force

An upward force exerted by a fluid (or gas) on an object immersed in it; equal to the weight of the fluid (or gas) that the body displaces.

Power

The rate at which work is done; unit is watt.

Voltage

The difference between the electric potentials of two points; unit is volt.

Electric Current

The amount of charge transported across a boundary per unit time; unit is ampere.

Resistance

The ratio of the voltage applied across a piece of material and the current through the material; unit is ohm.

Electric Dipole

A separated pair of positive charge (+q) and an equal amount of negative charge (-q).

Electric Lorentz Force

The force acting on a particle of charge, Q in an electric field, E.

Magnetic Lorentz Force

The force acting on a particle of charge, Q which moves at a speed v in a magnetic field, B.

Photon Energy

The energy of a photon with frequency f.

Visible Light

The range of electromagnetic radiation observable by the human eye (approximately 400-750 nm).

Minimal Energy of Gamma Photon

The minimum energy of a -photon needed for pair-production

Annihilation

The process in which 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.

Interference

The superposition of waves that results in the generation of a new wave pattern.

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.

Maximally Constructive Interference

Maximally constructive interference takes place, if the path difference (s) between the waves is an integer multiple of the wavelength ()

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.

Monochromatic Light

Light is monochromatic if its spectrum consists of a single wavelength only

Coherent Electromagnetic Radiation

Consists of photons capable of forming observable interference fringes.

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.

Singlet and Triplet State

In a singlet and a triplet state the number of unpaired electrons is zero and two, respectively.

Fluorescence Lifetime

The time during which the number of excited molecules decreases to 1/e-times (37 %) of its initial value.

Scintillation, Chemiluminescence, Photoluminescence

Processes where photon emission is elicited by ionizing radiation, chemical reaction and excitation by photons.

Fluorescence Quantum Efficiency (Yield)

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 de-excitation processes.

Index of Refraction

The index of refraction (n) gives the speed of light (c) in a given material

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).

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.

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.

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.

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.

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.

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.

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.

Isotopes

Isotopes are the variants of a chemical element with a given atomic number whose mass numbers are different.

Mass Defect of Nuclei

The mass defect equals the difference between the mass of a nucleus and the total mass of its constituents

Radioactive Radiation

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.

Electron Capture

Some nuclei are capable of capturing an electron residing on the K shell decreasing their atomic number by one.

Radioactive Decay Constant

Radioactive decay constant is equal to the inverse first power of the mean lifetime of a radioactive nucleus.

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.

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.

Attenuation Coefficient

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.

Directly Ionizing Radiations

Due to their charge, ionization is caused by the direct electrostatic interaction with atomic electrons. Their energy decreases in a series of ionizations along their path.

Indirectly Ionizing Radiation

Primary (direct) interactions between the photons and atomic electrons account for only 5% of ionizations. The majority (95%) of ionizations are caused by high-energy electrons emitted during the primary interactions.

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.

Ionization Detectors

Electrons and positive ions produced by the ionization process are separated by the electric field of the detector.

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.

Biological Effect of Radioactive Radiation

Excitation and ionization of atoms and/or molecules of living systems.

Hit in Radiation Biology

If one or more ionizations are produced in the radiosensitive volume of a biological object.

D37

D37 denotes the dose at which 37 % of the irradiated objects survive.

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.

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

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.

Effective Dose

Effective dose is the weighted sum of the equivalent doses in all specified tissues and organs of the human body (or other biological organism).

Cell Cycle and Radiosensitivity

Generally, the majority of cells are considered to be the most radiosensitive during mitosis and most resistant in late S phase.

Direct Radioimmunoassay (RIA)

An RIA is a very sensitive in vitro assay technique used to measure nano- or picomolar concentrations of substances.

Gamma-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.

SPECT

Images are taken from different directions by a -camera. The three-dimensional distribution of the radiation source is calculated from these images.

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.

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.

Nuclei in NMR

Whose resultant nuclear spin is different from zero; i.e. those nuclei which contain odd number of protons and/or odd number of neutrons.

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

Macroscopic Consequence of the Alignment of Nuclear Magnetic

f: resonance frequency N: gyromagnetic ratio of the nucleus Bext: external magnetic field

Pulsed NMR

Precession of transverse magnetization at right angles to the main magnetic field generated by a short radiofrequency pulse

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.

Signal Localization in MRI

In addition to the basic static magnetic field (B0) linear magnetic field gradients are applied in different directions.

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.

Ultrasound

Sounds whose frequency is between 20000 Hz and 1010 Hz.

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.

Reflection of Ultrasound

Extent of reflection is determined by the accoustic impedances of the two media. The greater the difference in their acoustic impedances, the larger the reflected fraction of ultrasound is.

Isolated System

A system is isolated if it doesn't exchange either energy or material with its environment.

Closed System

A system is closed when it can exchange energy, but no material with its environment.

Intensive Quantities

Physical parameters whose value does not depend on the size of the system are called intensive quantities.

Gibbs Free Energy

Gibbs free energy, G=H-TS, where H is the enthalpy, T is the absolute temperature and S is the entropy of the system.

Chemical Potential

Chemical potential is the Gibbs free energy of one mole of the given substance

Diffusion

Net flow of material propelled by Brownian motion due to a gradient of the chemical potential.

Diffusion Constant

The diffusion constant (D) is the amount of material transported through unit surface area in unit time at a unit concentration gradient

Osmosis

Flow of the solvent to a concentrated solution from the more dilute one, if the two compartments are separated by a semipermeable membrane.

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.

Amphipathic Molecules

They consist of hydrophobic and hydrophilic parts.

Passive Transport

Transport processes driven by the electrochemical potential gradient which do not need active metabolism are called passive transport.

Active Transport

Transport processes that results in material flow against the electrochemical potential gradient at the expense of energy utilization are called active transport.

Primary Active Transport

The transporter pumps ions/molecules across the membrane against their electrochemical gradient using energy from ATP hydrolysis.

Active Diffusion

The passive transport of small and lipid-soluble molecules across the membrane.

Ionophores

They promote the selective transport of ions through lipid membranes.

Factors contributing to the Maintenance of Resting Membrane Potential!

diffusion potential, Donnan potential and active transport by ion pumps.

Flux

Flux (J) is the amount of transported items across unit cross section area per unit time. Unit: mol/(m2s)

Conductivity

G (conductivity)=1/R (where R is the resistance) Unit: 1/ =siemens (S).

Action Potential

The action potential is a characteristic, time-dependent change in the membrane potential as a result of time- and membrane potential-dependent changes in the ion permeabilities of the membrane.