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Jacopo Biomembranes > Lecture 2 > Flashcards

Lecture 2 Flashcards

1
Q

What is the difference in ion conductance between biological membranes and pure phospholipids membrane?

A

The ion conductance of biological membranes is 2-3 order of magnitude greater than pure phospholipid bilayer.

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2
Q

Define simple diffusion:

A

Random movement of solute molecules in solvent tending toward an equilibrium state.

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3
Q

Define diffusion:

A

Movement from region of higher concentration to regions of lower concentration.

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4
Q

What is the rate of diffusion (J) proportional to?

A

It is proportional to the concentration gradient over the distance x.

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5
Q

What is the rate of diffusion independent of?

A

The rate of diffusion of other substances

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6
Q

What is the rate of diffusion dependent of?

A

1) Physical properties of solute and solvent molecules. 2) Temperature 3) Electric field

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7
Q

Define each term of Fick’s Law of Diffusion:

A

J=rate of diffusion (mol/sec) P= Permeability coefficient of solute across membrane (m/sec) A= Membrane area (m2) S= solute concentration in each solution (mol/m3)

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8
Q

How is a general flow calculated?

A

Flow=energy gradient/resistance

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9
Q

What is Kp and how is it calculated?

A

Kp is lipid-water partittion coefficient and it is Acm/Ac.

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10
Q

What is the value of Kp for hydrophilic molecule?

A

It is <1

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11
Q

What is the value of Kp for hydrophobic molecule?

A

It is >1

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12
Q

What does the Stroke’s law says?

A

That a perfect sphere travelling through a viscous liquid feels a drag force proportional to the frictional coefficient (1/nxr)

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13
Q

What is the rate of diffusion PROPORTIONAL to?

A

1) Permeability coefficient P 2) Surface of the membrane A 3) Concentration difference Δc

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14
Q

Lists the three frictional effects that affect membrane permeability:

A

Molecular size Molecular shape - straight (“snake-like”) P increases; globular P decreases Membrane viscosity - Short R chains, -C=C-, inc. To, P increases

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15
Q

Define osmosis:

A

Water moves from region of higher to lower (more negative) water potential, showing bulk flow

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16
Q

What is osmolarity proportional to?

A

Directly proportional to concentration of dissolved solutes and inversely proportional to osmotic potential. Inversely proportional to osmotic potential

17
Q

What are the experimental protocols membranes commonly used?

A

1) Artifical bilayer, lipid films, proteoliposomes 2) Natural membrane vesicles 3) Intact cells 4) Perfused tissue

18
Q

What are the three methods commonly used to study membranes in experimental protocols?

A

1) Measure change in solutes concentration 2) Tracer techniques 3) Electrical measurements

19
Q

Describe diffusion of solute in solution:

A

Rapid diffusion over short distances

20
Q

Describe diffusion of solute across membrane:

A

Membrane is a selective barrier to diffusion

21
Q

Where does the concentration gradient lies in diffusion of solute across a membrane?

A

Concentration gradient lies within the membrane barrier

22
Q

What is permeability equal to overall?

A

Diffusion + Partitioning

23
Q

What are the two processe for which diffusion of solute across a membrane is vital?

A

Gas exchange (CO2 and O2) Lipophilic drug action

24
Q

What is solute concentration difference across a membrane relevant for?

A

It is also relevant for solvent (water potential) gradient, also called osmotic water flow.

25
Q

What are the values of P and D specific for?

A

They are specific for membrane and diffusing molecule.

26
Q

What are the four important factors for predicting passive permeability?

A

Frictional effects, lipid solubility, unstirred layer and charge effects

27
Q

Describe unstirred layer:

A

It increase the overall thickness of barrier

28
Q

Describe the two charge effects:

A

Molecular charge affects Kp and hydrogen bonding alters the effective size/shape

29
Q

What are the major solutes in cellular and external water pools:

A

Inorganic ions.

30
Q

Describe the lipid cell membrane as a barrier to ion permeation:

A

Very low ion permeability because it is an electrical insulator and differential ion permeability

31
Q

What is donnan equilibrium a result of?

A

It is a result of the fact that permeability differences have a major effect on ion distirution across the cell membrane.

32
Q

What does the fact that animal cell exerts minimal turgor pressure:

A

In this case, water potential is equal to osmotic potential (zero for pure water, increasing negative as solute concentration increases).

33
Q

Describe the osmolarity of an hyposmotic solution:

A

Less than 0.3 osmol/l

34
Q

Describe the osmolarity of an hyperosmotic solution:

A

Higher than 0.3 osmol/l

Jacopo Biomembranes (16 decks)

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