Term
| True:False The rate of simple diffusion across a concentration gradient is exponential and unsaturable. |
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Definition
False!
Linear and unsaturable |
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Term
| Through post-translational modification, a large polar molecule loses its net-positive charge and becomes electrostatically neutral (it is still polar). What effect will this change have on the molecule's partition coefficient and passive diffusion across membranes? |
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Definition
Charged species are less able to dissolve in hydrophobic lipids, so the partition coefficient would likely go up if the molecule lost its (+) charge.
However, since only small, polar molecules such as ethanol (as well as hydrophobic molecules and gases) can passively diffuse across membranes, this change would probably not be enough to get it across the membrane. |
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Term
| True:False Water can move against its concentration gradient through Aquaporins in an ATP-dependent manner. |
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Definition
False!
Water ONLY moves down its concentration gradient by facilitated diffusion through Aquaporin channels. |
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Term
| Provide a general explanation of how osmotic pressure, acting through aquaporins, relates to edema. |
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Definition
| Remember, osmotic pressure is generated as the [solutes] in water increases (making the [water] low). This pressure draws more water into solution, which in the case of edema manifests as excess fluids in tissues. |
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Term
| What is the consequence of mutations in aquaporin channels as seen in nephrogenic diabetes insipidus? |
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Definition
| Great deal of water loss in the form of dilute urine. Individuals cannot uptake water from hypotonic urine solution. |
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Term
| How is a negative membrane potential (-70mV) maintained in cells? |
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Definition
Na/K pump takes 3 Na out and 2 K in, making the [Na} inside the cell low and the [K] inside the cell 20X greater than outside (more positive charge being taken out for the amount being brought it).
Some K also leaves the cell interior along its concentration gradient.
Together, these two factors create a negative intracellular potential. |
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Term
| What is the most important result demonstrated by patch-clamp experiments? |
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Definition
| Cycling of open-closed states is fast in membranes, with more time spent open |
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Term
| What are 3 types of ion channel gating? |
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Definition
1) Ligand (neurotransmitter)
2) Voltage (synapse charge flux)
3) Mechano-gated (muscle stretch receptors) |
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Term
| Uniporters transport amino acids, nucleosides and sugars. What are some characteristics about their transport mechanism? |
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Definition
1) 1 molecule at a time DOWN a concentration gradient
2) Initial rate > simple diffusion
3) Partition coefficient irrelevant (not true for passive)
4) Saturable (remember, passive is not)
5) Specific (Glut1 only transports D-gluclose)
6) Competition |
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Term
| Is a very low partition coefficient or a high molecular concentration more likely to affect Uniport transport of that molecule? What about passive transport? |
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Definition
Uniport is Saturable and independent of partition coefficient
(Answer= high concentration of molecule)
Passive transport is not saturable but does depend on hydrophobicity and charge
(Answer = partition coeficient) |
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Term
| Why are symport and antiport carriers referred to as examples of Secondary Active Transport? |
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Definition
| These kinds of cotransport systems do not directly use ATP to transport molecules across membranes, but they utilize ion gradients that are generated by ATP powered pumps. |
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Term
| In Falconi syndrome, substances cannot be carried back across the kidney cells into the blood, and are excreted in the urine. What type of deficit is this? |
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Definition
Na+ Symport Issue
Recall, Na+/Glucose symporters also move glucose against its concentration gradient from the intestinal lumen into the cell by "piggybacking" on the Na+ concentration gradient. |
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Term
| How is muscle relaxation maintained? What does it have to do with the Na+K+ ATPase? |
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Definition
1) Cationic, Na+/Ca2+ antiport.
Calcium is moved out of the cell, against its concentration gradient, as 3Na+ is brought in down its concentration gradient.
2) The process also relies on the electrical potential generated by the Na+K+ ATPase |
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Term
| How are ouabain and digoxin used to increase cardiac contractility? |
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Definition
| They inhibit the Na+K+ ATPase pump, thereby depleting the Na+ gradient and inhibiting the efficiency of Na-Ca antiport-mediated muscle relaxation. |
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Term
| Why is Cl-/HCo3- anionic antiporter transport in RBCs not dependent upon electrical potential gradients? |
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Definition
There is a one for one exchange of anions, making the direction of the reaction only dependent on the concentration gradients and not the charge.
Recall, these transport systems function in opposite directions when a RBC is in systemic capillaries versus the pulmoanry capillaries |
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Term
| How is anionic antiport transport involves in converting waste carbon dioxide into water-soluble bicarbonate ions? |
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Definition
In systemic capillaries (in the body),
1) C02 diffuses from plasma into erythrocytes
2) Carbonic Anhydrase turns it into HCO3-
3) As the [HCO3-] increases, it moves from cytosol to blood plasma, down its concentration gradient, in exchange for Cl-
4) O2 is released from Hb, causing Hb to conformationally shift to bind free H+.
In Pulmonary capillaries (in the lungs)
1) Elevated plasma HCO3- moves into RBC in exchange for Cl-
2) H+ is displaced from Hb by O2
3) Carbonic Anhydrase drives the reverse reaction with free H+ and bicarbonate ion
4) CO2 diffuses through the membrane into the blood plasma and into exhaled air! |
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Term
1) What type of ATPase is the Na/K ATPase?
2) How does it work? |
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Definition
1) P-type (tetrameric transporter is phosphorylated on larger alpha subunit)
2) Short answer: Takes 3Na+ out and 2K+
(E1 binds Na on inside, phosphoryation changes E1 to E2, E2 drops off Na and binds K on outside, dephosphorylation changes E2 to E1, E1 drops of K on inside)
- E1 and E2 states
- E1 has 3 high affinity Na sites and 2 low affinity K sites on intracellular side
- Na binding stimulates ATP-dependent phosphorylation of E1, causing it to become E2
- E2 has same 5 sites, but opposite affinities (i.e. it binds K more readily)
- K-binding stimulates dephosphoryation on cytoplasmic side of E2, reversing the confirmation again to E1. |
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Term
| What role does the H/K ATPase play in the stomach? What is Prilosec? |
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Definition
Acidifies lumen of stomach.
Prilosec is a non-competitive inhibitor of the pump. |
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Term
| What type of ATPase is the ATP synthetase? |
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Definition
F-type ATPase
Transports H1 and couples this to the production of ATP from ADP and Pi in mitochondria and chloroplasts |
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Term
| What type of ATPases are found in lysosomes and endosomes? What do they do? |
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Definition
1) V-type ATPases
2) Transport H+, acidifying vesicular lumens to pH 4-5 (1000-fold proton gradient b/w lysosomal lumen and cytoplasm). Powered by ATP binding and hydrolysis but NOT phosphorylation. |
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Term
| V-type ATPases are phosphorylated in the lumen of lysosomes. What happens? |
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Definition
| Nothing. Trick question. They are regulated by ATP binding and hydrolysis. |
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Term
1) Why are ABC transporters (ATP Binding Cassettes) associated with drug-resistance cancer?
2) How do they act? |
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Definition
They pump drugs out of cells! Also pharmacologically relevant b/w of this.
2) Flipase actions where the hydrophobic molecule to be transported binds the ABC transporter in the inner lipid membrane and the ABC molecule flips the molecule to the other half o fthe bilayer, where it diffuses out. |
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Term
| What 6 instances of toxin removal heavily rely on ABC transport? |
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Definition
1) Kidney tubules- urine
2) Intestinal lining- fecies
3) Liver bile canaliculi- bile in fecies
4) Brain capillary lining- B-B barrier
5) Sertoli cells of testis- Blood-testis barrier
6) Trophoblast placental cells- Maternal-fetal barrier |
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