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32 Cards in this Set
- Front
- Back
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1. Why do we care about cell membranes and diffusion?
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1. If a cell membrane breaks, the cell dies
2. Cell membranes create and maintain concentration differences bwt the intracellular and extracellular solutions **This gives resting membrane potential and action potentials **These concentration differences are the basis for signaling by the nervous system |
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2. How is the cell membrane?
What is the basic function of the cell membrane? |
Mechanically fragile
Separates two aqueous solutions w/ different compositions |
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3. What are the ICF concentrations of Na, K, Ca, H, pH?
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Na: 10 mM
K: 135 mM Ca: 100 nM H: 100 nM pH: 7.0 - 7.2 |
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4. What are the ECF concentrations of Na, K, Ca, H, pH?
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Na: 142 mM
K: 4 mM Ca: 1 mM H: 40 nM pH: 7.4 |
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5. How do concentrations and conditions differ from the inside and outside?
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1. Much higher K inside than outside
2. Higher Ca, Na, Cl outside than inside 3. ECF is slightly alkaline; ICF is closer to neutral 4. Osmolarity of ICF and ECF is normally the same (290 mOSM) |
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6. In terms of neutrality how are the ICF and ECF?
What law describes this? What maintains the composition of the ECF? What makes sure the ICF has the proper composition? |
Both electrically neutral
**equal numbers of positive and negative charges Law of Electroneutrality Kidney Cell membrane **dynamic regulator of the cell interior and is the cell's communications interface |
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7. What is the composition of the cell membrane?
How is the membrane in terms of thickness? What does this result in? |
Phospholipids and proteins
Thin (75 - 100 A) Mechanically weak **Can't contain pressure and swelling will cause the cell to burst |
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8. What is the fluid mosaic model?'
What is a common phospholipid? What does this contain? |
Proteins are immersed in "a sea of phospholipid"
Phospholipids are present as a bilayer Phosphatidylcholine 1. Glycerol backbone 2. Two fatty acids esterified to the glycerol 3. Phosphate group attached to glycerol 4. Choline **as a whole it has no charge |
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9. How are the phospholipids arranged in a bilayer?
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Hydrocarbon tails of FA create a hydrophobic core to the bilayer
FA are esterified to the glycerol backbone Phospholipid head group is hydrophilic b/c has both pos N and a neg O Head groups face the cytoplasm and the ECF **interactions w/ proteins and water are maximized for stability |
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10. How do saturated and unsaturated FA differ?
How do unsaturated FA pack in a membrane? |
Saturated: no C-C double bonds
Unsaturated: has C=C -have a "kink" in the tail Do not pack as well b/c due to the double bond there is no rotation **Membrane is not as tightly packed and is said to be more "fluid" |
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11. What are the two types of membrane proteins?
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1. Peripheral
-exposed on only one side of the bilayer -can be removed more easily 2. Intrinsic or integral -membrane spanning -exposed to both IC and EC solutions -most are free to move in the bilayer -some might be anchored to cytoskeleton via contractile filaments |
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12. What are some hydrophobic solutes?
How do these get through/across the membrane? |
Oils, FA, fat soluble vitamins and drugs
Dissolve in the phospholipid bilayer and diffuse across Even large hydrophobic solutes dissolve in the membrane and diffuse across |
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13. What are some hydrophilic solutes?
Can these dissolve and diffuse? How do they get through/across the membrane? |
Ions, water, hydrophilic solutes
No Routes through integral proteins called channels or pores |
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14. What are channels?
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Made of one or more integral protein subunits that span the membrane and selectively allow certain ions to cross
Respond to concentration and voltage differences |
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15. What are some characteristics of channels?
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1. Rapidly and randomly open and close
2. Often regulated by voltage or the binding of certain small molecules |
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16. What are pores?
What are "aquaporins"? |
Hypothetical hydrophilic pathways through the membrane that are not regulated
Family of proteins responsible for pores Most movement of water through cell membrane occurs through aquaporins **few small hydrophilic solutes can also pass through some kinds of aquaporins |
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17. What happens if a hydrophilic solute has more than 5 or 6 C atoms?
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It won't be able to cross the cell membrane at all unless there is a carrier mediated transport mechanism
Examples: -faciliated diffusion carrier -exchanger -cotransporter -pump |
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18. How can the bind of H affect a solute (weak base and acid)?
What is an example? |
Binding of H can change the solute behavior
Lidocaine works by binding to Na channels but must enter nerve to get to binding site Uncharged form can dissolve in membrane and diffuse across If protonated (in acidic solution) it cannot dissolve in membrane and diffuse into cells |
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19. What are electrolytes?
How is the diffusion of non-electrolytes? |
Substance that dissociates into positively charged particles (cations) and negatively charged particles (anions) when they dissolve in water
Net diffusion is always from a high concentration to low Diffusion tries to reach an equilibrium where concentrations are the same everywhere **concentration difference is the driving force |
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20. How is the net flow of a non-electrolyte through a porous membrane?
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Net flow of the solute by diffusion is the difference bwt the two unidirectional flows
Each unidirectional flow is proportional to the concentration on the side it is coming from **Net flow is directly proportional to the concentration difference |
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21. What is flux (J)?
How does cross sectional area and membrane thickness affect flow? |
Flow per unit area
Bigger cross sectional area (A) will allow more flow Thicker membrane (larger ∆x) will allow less flow |
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22. How is the net flux?
What is the proportionality constant? What is this called mathematically? |
Directly proportional to the concentration difference (∆C)
Inversely proportional to the membrane thickness (∆x) D the diffusion coefficient Fick's First Law of Diffusion **it holds for diffusion through membranes and also in free solution |
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23. How fast do things move by diffusion?
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Distance a particle moves is proportional the square root of time
Doubling time only increases distance by √2 **∆x (distance moved) is not a linear function to time |
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24. How is diffusion related to distance?
What does the slope represent? |
Diffusion is fast process over short distance
Diffusion is slow process over long distance Velocity **steep = high velocity **shallow = low velocity |
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25. What happens when a non-electrolyte diffuses across a non-porous membrane?
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Solute dissolves in the lipid membrane and the concentration of the solute in the membrane is not the same as it is in the bulk solution next the membrane
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26. What is the oil-water partition coefficient, Kp?
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Expresses the phenomenon of different solubility of a solute in oil and water or partitioning
Kp = (solubility in oil)/(solubility in water) |
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27. What do the different values of Kp mean?
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Kp > 1 means solute prefers to be in oil (hydrophobic)
Kp < 1 means solute prefers to be in water Kp = 1 means solute has no preference |
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28. What do difference values of Kp mean in terms of partitioning into the membrane?
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Kp > 1 means concentration in membrane in will be higher than it is in water
Kp < 1 means concentration in membrane will be lower than it is in water Kp = 1 means concentration in membrane and water will be the same |
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29. How does the value of Kp relate to the concentration gradients?
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Kp > 1 "amplifies" the concentration gradient
**more rapid diffusion Kp < 1 "decreases" the concentration gradient |
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30. How can flux be represented in relation to permeability?
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Flux is the product of the permeability and the concentration difference (∆C)
A positive value of flux means there is a net outward flux of a solute from a cell |
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31. Based on what two things can the permeability of a solute be predicted?
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1. Its size (small things diffuse quickly)
2. Its oil-water partition coefficient (things that dissolve well in the membrane enter the cell quickly) |
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32. Why do small hydrophilic solutes enter cells more quickly than expected?
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1. Due to the concept of "pores"
2. Small hydrophilic solutes are believed to enter through pores (aqueous pathways through integral proteins) |
