Membrane transport of small molecules, and the electrical properties of membranes

Question 1

What is the intracellular concentration of Na+?

Answer 1

10 mM

Question 2

What is the extracellular concentration of Na+?

Answer 2

145 mM

Question 3

What is the intracellular concentration of K+?

Answer 3

140 mM

Question 4

What is the extracellular concentration of K+?

Answer 4

5 mM

Question 5

What is the intracellular concentration of Mg2+?

Answer 5

.5 mM

Question 6

What is the extracellular concentration of Mg2+?

Answer 6

2 mM

Question 7

What is the intracellular concentration of Ca2+?

Answer 7

100 nM

Question 8

What is the extracellular concentration of Ca2+?

Answer 8

2 mM

Question 9

What is the intracellular concentration of H+?

Answer 9

70 nM

Question 10

What is the extracellular concentration of H+?

Answer 10

40 nM

Question 11

What is the intracellular concentration of Cl-?

Answer 11

10 mM

Question 12

What is the extracellular concentration of Cl-?

Answer 12

110 mM

Question 13

How does size effect a molecules chance of getting through the membrane?

Answer 13

The smaller the molecule the more easily it can pass through the membrane.

Question 14

How does electrical charge effect a molecules chance of getting through the membrane?

Answer 14

It causes association with water, water crowds around the charge, it makes it so the membrane is basically completely impermeable to charged molecules due to water association.

Question 15

How does lipid-solubility/polar vs non polar effect a molecules chance of getting through the membrane?

Answer 15

Non polar molecules travel easily through the membrane. Even large nonpolar entities can cross the membrane.

Question 16

Rearrange in order of highest permeability to lowest. Polar small, ions, polar large, nonpolar (large and small).

Answer 16

Small and large nonpolar (all can cross), small polar, large polar, ions (none will cross).

Question 17

How do ions cross a membrane?

Answer 17

Through membrane proteins.

Question 18

How do channel proteins work?

Answer 18

They have a pore in their center which is shielded from the nonpolar nature of the membrane. This pore, sometimes made by incomplete alpha helices, provides a point water can enter, it also allows for the transport of ions through at a quick rate.

Question 19

What are the units of flux rate (flux rate in its use of ions crossing through a single membrane protein)?

Answer 19

Ion/second

Question 20

What is the flux rate of a channel protein?

Answer 20

10^7or8 ions per second. It has the fastest rate, since a channel protein has unrestricted flow through it’s aqueous pore.

Question 21

Transporter proteins, how do they work?

Answer 21

They bind with a higher affinity, to the substrate. They then toggle positions. So if the protein translated Ca2+ out of the cell, it would start open to the interior of the cell, calcium would come in and bind, It would shift to being closed to both the extra and intracellular space, then the extracellular space. Once in the extracellular formation the Ca2+ would no longer have the same affinity for the binding site (since the protein has shifted) it would leave allowing the protein to shift back the open to intracellular position.

Question 22

What is a transporter enzymes average flux rate?

Answer 22

10^3 ion/sec

Question 23

Differentiate between passive and active transport.

Answer 23

Passive requires no energy, movement is down concentration gradient. Active requires energy. Movement is against concentration gradient.

Question 24

Primary active transport: (go for it)

Answer 24

Primary active transport is the process through which ATP is used to cause movement of Ions against their concentration gradients. An example is the Na+/K+ ATPase pump system.

Question 25

When does simple diffusion become predominant over transport mediated?

Answer 25

Transport mediated will have a Km Vmax plot. While transport mediated will have this Vmax cut of point, passive diffusion will not, it will just be based on the magnitude of the concentration gradient.

Question 26

Coupled proteins:

• uniport (non coupled)
• symport
• antiport

Answer 26

Uniport: one molecule is moved out or in
Symport: two different molecules are moved into the cell or out of the cell at the same time
Antiport: Two molecules are moved opposite directions at the same time.

Question 27

Secondary active transport

Answer 27

Secondary active transport involves a non-ATP mediated energy source to drive transport against the membrane. This could be a coupled symport receptor where one molecule is being moved down its concentration gradient and the other is being moved against its concentration gradient. This could also be a light driven pump, go photosynthesis.

Question 28

How is differential localization of transport proteins achieved?

Answer 28

Tight junctions: the protein will have segments that bind completely with each other, stopping movement of proteins through tight junction regions, and creating protein localization.

Question 29

What is FRAP?

Answer 29

Fluorescence Recovery After Photobleaching

Question 30

How does FRAP work?

Answer 30

You attach a Fluorescent dye to the proteins, you then with a laser bleach a segment of this dye (so it is no longer returning fluorescence). You measure the rate at which the fluoresced dye comes back to this bleached segment and the rate at which the bleached molecules spread out into the nonbleached. Basically we will see a gradual return of fluorescence to this location. We can measure that change and equate it to the rate at which these proteins diffuse through the membrane. Assuming we have already taken into account corrals.

Question 31

Membrane corrals. Tell me details.

Answer 31

These corrals are caused by the placement of protein anchors connected by spectrin (actin) filaments. This is also referred to as the membrane skeleton fence. These spectrin filaments are on the cytosolic side of the plasma membrane and are laid out in a hexagonal grid. They provide structure and restrict to some degree the diffusion of proteins past the fence. Allowing proteins to be placed in specific locations, and at least sort of stay there. It is also an important structural component.