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38 Cards in this Set

  • Front
  • Back
180. What does it mean that lipids are amphipatic molecules?
They consist of hydrophobic and hydrophilic parts.
181. 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.
182. What are the possible phase states of biological membranes?
- gel state
- liquid crystal (fluid) state.
183. What kind of things are able to 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
- increase in the relative protein content of the membrane.
- increase in the extracellular Ca2+ concentration.
184. How does cholesterol change the viscosity of lipid lipid membranes?
Below the transition temperature it usually decreases, above the transition temperature it increases.
185. What is the magnitude of the lateral diffusion constant of lipids and proteins in biological membranes?
lipids: 10^-8 - 10^-9 cm^2/s
proteins: 10^-9 - 10^-12 cm^2/s.
186. What kind of methods are able to measure the rotational diffusion of lipids and proteins, respectively, in biological membranes?
- proteins: phosphorescence anisotropy, ESR
- lipids: fluorescence anisotropy, ESR
187. What methods are able to measure the lateral diffusion of proteins in biological membranes?
- FRAP: with fluorescently labelled antibodies
- ESR.
188. How can the molecular weight of membrane proteins be determined?
- SDS gel-electrophoresis
- gelfiltration
- sedimentation equilibrium and velocity methods.
189. What patterns of membrane proten distribution can be observed after crosslinking membrane proteins with antibodies?
- diffuse distribution
- patch and cap formation.
190. What can be the explanation for the decreased lateral mobility of a membrane protein?
1. anchoring by the cytoskeleton
2. association of the protein with other membrane proteins
3. aggregation of the protein in question
4. localization of the protein in question at membrane contact surfaces.
5. decrease in the membrane fluidity
6. the protein cannot cross the border of lipid domains.
191. For what kind of molecules is the permeability of biological molecules the highest?
For small, uncharged molecules, apolar, e.g. O₂, N₂.
192. How can membrane proteins be divided into groups according to their function?
- transport and channel proteins
- receptor proteins
- enzymes
- signal transducing proteins
- structural membrane proteins.
193. What is the concentration of Na+, K+ and Ca2+ ions in the extra- and intracellular spaces, respectively?
extracell. intracell.
Na+ 140mM 10-20mM
K+ 5mM 140-150mM
Ca2+ 1-2mM 10^-4mM
194. What is passive transport?
Transport processes driven by the electrochemical potential gradient which do not need active metabolism are called passive transport.
195. What is active transport?
Transport processes that results in material flow against the electrochemical potential gradient at the expense of energy uptake are called active transport.
196. What are the properties of facilitated or carrier-mediated diffusion?
- transported proteins specifically bind the transported molecules
- It is inhibited by specific inhibitors
- The flux of transport can be saturated over a given concentration of the transported material.
197. a., Can the direction of ion transport of the Na+/K+ ATPase be reversed?
b., If yes, how?
c., If no, why?
a., Yes, it can be reversed.
b., By drastic changes in the concentration gradients of K+ and Na+
c., -
198. 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 channels
- mechanical deformation (stretch) activated ion channels.
199. What is the function of ionophores?
They promote the selective transport of ions through lipid membranes.
200. How can ionophores be grouped according to the mechanism of ion transport?
- carrier ionophores
- channel forming ionophores
201. List the factors contributing to the material of quiescent membrane potential!
- diffusion potential
- Donnan potential
- active transport by ion pumps.
202. Write the Nernst equation!

where 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.
203. 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.
204. Are the ions on the two sides of the membrane of a living cell in thermodynamic equilibrium?
No. There is no thermodynamic equilibrium because the net passive flux of a given ion is not zero at the resting membrane potential.
205. Describe the relationship between net fluxes of major permeating ions in the case of resting membrane potential!
where Jx is the flux of ion x(sorry it's what they gave me)
206. Give the definition and unit of flux!
Flux (J) is the amount of transported item across unit cross section per unit time. Unit: mol/(cm^2/s)
207. Give the Goldmann-Hodgkin-Katz equation!
too long to type
208. Give the definition and unit of conductivity!
G (conductivity)=1/R (where R is the resistance)
Unit: 1/Ω =siemens (S).
209. Give the current carried by ion x through the cell membrane if the membrane potential is Em!

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.
210. What is the principle of voltage-clamp?
The membrane potential is held at a controlled value independently of ion currents through the membrane.
211. Internet the generation of the action potential according to the Goldmann-Hodgkin-Katz equation!
The action potential is the result of membrane potential and time dependent changes in the permeability of Na+ and K+ ions. In the depolarization phase the Na+ permeability is dominant, the subsequent repolarization is the result of a decrease in Na+ permeability and an increase in K+ permeability at the same time.
212. 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, current-clamp)
213. What kind of currents can be measured by means of patch-clamp?
- single channel currents (e.g. cell-attached configuration)
- ion currents flowing through the entire membrane of the cell (whole-cell configuration).
214. What are the most important features of ion channels?
- selective permeability: the channel is permeably only to a certain ion species;
- gating: the trasition between open and closed states of the channels are regulated by specific signals.
215. What voltage differences can be detected during the R waves of an ECG measured between different points of the body surface?
216. Write down the Einthoven-Waller rule and interpret the variables in the formula!
R1 + R3 = R2

where R1, R2 and R3 are the projections of the integral vector on the sides of the Einthoven triangle.
217. What is the meaning of an ECG curve in the case of
A. unipolar
B. bipolar leads?
A. It is the potential difference between an exploring and a reference electrode
B. It is the potential difference between two exploring electrodes.