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Matt's MCBG Exam 2 Study Guide > 8/29/14 - Electrical Properties of Membranes > Flashcards

8/29/14 - Electrical Properties of Membranes Flashcards

1
Q

How does permeability of the lipid membrane differ for different types of molecules?

A

Small hydrophobic molecules can pass through the bilayer unassisted. Small/large uncharged polar molecules typically need assistance in passing through. Ions cannot pass through the bilayer unassisted.

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2
Q

What are the major types of transport proteins?

A

Channel mediated proteins and transporter mediated proteins

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3
Q

What percentage of all membrane proteins are transport proteins?

A

15-30%

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4
Q

What is the difference between passive and active transport?

A

Passive transport relies on the diffusion of molecules along a gradient, and active transport requires energy input (ATP) to move a molecule against its gradient.

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5
Q

What is a combinatorial membrane gradient?

A

A combination of the concentration gradient and electrical gradient across a lipid membrane.

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6
Q

What are the 3 different types of ion channels?

A
  1. Voltage-gated
  2. Ligand-gated (intracellular or extracellular)
  3. Mechanically gated
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7
Q

True/False: if the membrane potential is above a certain threshold, all channels will be open

A

False. Channels are not simply all open or closed, the percentage of open channels increases with membrane voltage.

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8
Q

What mechanism do transporter proteins use to transport solutes into/out of the cell?

A

Conformational changes allows the exchange of material between 2 sides of the lipid membrane.

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9
Q

What is the difference between primary and secondary active transport?

A

Primary uses ATP directly, secondary uses energy stored in electrochemical gradients to power the movement of molecules.

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10
Q

What are the 3 different types of transport molecules? (important)

A
  1. Uniport
  2. Symport
  3. Antiport
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11
Q

How does a uniport molecule function?

A

A molecule is directly transported from one side of the lipid membrane to the other.

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12
Q

How does a symport molecule function?

A

A molecule and its co-transported ion are transported from one side of the lipid membrane to the other.

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13
Q

How does an antiport molecule function?

A

A molecule is transported from one side of the lipid membrane to the other and its co-transported ion is transported in reverse.

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14
Q

What is the most commonly used ion for coupled transport?

A

Sodium

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15
Q

How is glucose transported into the cell?

A

Active transport against its own gradient by a transporter protein powered by a sodium gradient.

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16
Q

What are the 3 types of ATP-driven pumps and how do they differ?

A
  1. P-type pumps are phosphorylated during ion transport.
  2. F/V-type pumps: F makes ATP using an electrochemical gradient, V then hydrolyzes ATP to pump H+ across membrane.
  3. ABC transporters pump molecules while hydrolyzing ATP.
17
Q

How is a sodium gradient established and maintained?

A

The Na+/K+ pump uses ATP to move 3Na+ out of a cell in exchange for moving 2K+ into the cell.

18
Q

How much of our energy is dedicated to maintaining a sodium gradient?

A

1/3

19
Q

Describe the 4 steps by which the Na+/K+ pump works. (draw out? needs work) (important)

A
  1. Na+ binds, ATP hydrolyzed
  2. Conformational change occurs and Na+ is transferred
  3. K+ binds on extracellular surface following conformational change, dephosphorylation occurs.
  4. K+ transferred with dephosphorylation-induced conformational change.
20
Q

How do ABC transporters function?

A

ATP hydrolysis powers a conformational change that allows small, non-ionic molecules to pass through the membrane.

21
Q

ABC transporters are relevant to which two common diseases?

A
  1. Cystic fibrosis (ABC transporter can’t transport Cl- from the cell, it accumulates within)
  2. Malaria (ABC transporter pumps anti-malarials from the cell)
22
Q

What is cystinuria?

A

A genetic defect in an amino acid transporter responsible for removing cystine from urine and the intenstine. Affected individuals develop cystine stones in their bladders and kidneys

23
Q

How is glucose transported from the intestinal lumen into the extracellular fluid?

A

It passes through a sodium-glucose symport on the apical side of the epithelium against its concentration gradient. On the basal side, glucose passively diffuses out of the cell into the extracellular fluid.

24
Q

Where are concentrations of Na+ and K+ highest?

A

Na+ is highest in extracellular environment. K+ is highest in intracellular environment.

25
Q

What is the Nerst equation?

A

For a given ion, Vk = (RT/zF)*ln(Xo/Xi)

where (RT/zF) is a given constant and X is a given ion.

26
Q

What is the average resting membrane potential for a cell?

A

-70mV

27
Q

What happens to ions in a cell if Vk is more negative than Vm?

A

Positive ions will leave the cell and/or negative ions will enter the cell.

28
Q

What happens to ions in a cell if Vk is more positive than Vm?

A

Positive ions will enter the cell and/or negative ions will leave the cell.

29
Q

What is Vk and Vm?

A

Vk is the Nerst potential or equilibrium potential for a given ion. Vm is the membrane potential.

30
Q

What are the Nerst potentials for calcium, sodium, chlorine, and potassium?

A
  1. Ca+2: 125mV
  2. Na+: 70mV
  3. Cl-: -65mV
  4. K+: -90mV
31
Q

Describe the the movement of sodium across a cell membrane at resting membrane potential.

A

The Vk of sodium is +70mV, and the resting potential of a cell is -70mV. Since the Vk is more positive than the Vm, sodium will want to enter the cell. If a sodium channel is opened, it will rapidly move into the cell due to the large difference in potential.

32
Q

Describe the movement of potassium across a cell membrane at resting membrane potential.

A

The Vk of potassium is -90mV, and the resting potential of a cell is -70mV. Since the Vk is more negative than the Vm, potassium will want to leave the cell. If a potassium channel is opened, it will slowly move out of the cell due to the small difference in potential.

33
Q

What is positive voltage?

A

Positive voltage = positive current. Positive current refers to a positive ion leaving the cell or a negative ion entering the cell.

Matt's MCBG Exam 2 Study Guide (13 decks)

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