Membranes And Membrane Transport

Front 1

Which type of molecules move across the lipid bilayer by simple diffusion?

Back 1

Small, uncharged or hydrophobic molecules

Front 2

Which type of molecules require specialist proteins (pumps, transporters, pores) to carry them across the membrane?

Back 2

Charged, polar molecules

Front 3

Permeability of the lipid bilayer is higher for molecules that are .....

Back 3

Uncharged, non-polar and small.

Front 4

What are two examples of charged, polar molecules that cannot freely cross a membrane?

Back 4

Amino acids and ATP

Front 5

What is the concentration of sodium like on the inside of the cell compared to the outside?

Back 5

In = 10 mM

Out = 140 mM

Front 6

What is the concentration of potassium like on the inside of the cell compared to the outside?

Back 6

In = 140 mM

Out = 4 mM

Front 7

What is an example of secondary active transport?

Back 7

Na+/Glucose transport

Front 8

What is an example of primary active transport?

Back 8

Na+/K+ ATPase

Front 9

The rate of diffusion depends on what two things?

Back 9

1. Concentration gradient

2. Partition coefficient

Front 10

What is the partition coefficient? (K ow)

Back 10

The equilibrium constant for the partitioning of a molecule between oil (octanol) and water.

K ow = [amount dissolved in oil] / [amount dissolved in water]

Front 11

The higher the K ow value, the more or less lipid soluble a molecule is?

Back 11

The more lipid soluble

Front 12

The K ow of diethyl urea is 0.01. What does this tell you about its solubility in water compared to oil?

Back 12

Diethyl urea is 100 times more soluble in water than octanol.

Front 13

Discuss how potassium moves through the K+ channel

Back 13

Potassium is hydrated by water and when it moves though the channel. It is energetically unfavourable to just ripe off water sothe water is substituted by oxygen from the amino acids

Front 14

Why can Na+ not pass through the K+ channel?

Back 14

Na+ is smaller than K+ so it can't fit in the selectivity filter so won't shed off water molecules.

Front 15

What are the two types of ligand gated channels?

Back 15

Extra-cellular ligand gated and intracellular ligand gated

Front 16

When the external concentration of solute is plotted against the rate of uptake, what do the curves look like for carrier mediated transport and simple transport?

Back 16

Front 17

What is J max?

Back 17

The maximal transport

Front 18

The lower the Km of a transporter, the higher or lower the affinity for its substate

Back 18

The higher

Front 19

What regulates the expression of GLUT4?

Back 19

Insulin

Front 20

How is GLUT4 regulated by insulin?

Back 20

Insulin binds to membrane receptor, this signals to intracellular pool of GLUT4. Vesicles storing GLUT4 transporters translocate GLUT4 to plasma membrane. When insulin levels fall, GLUT4 recycled to pool.

Front 21

Movement of solute against the concentration gradient requires energy. What is the source of energy in primary active transport?

Back 21

Hydrolysis of ATP

Front 22

What is the source of energy in secondary active transport?

Back 22

The electrochemical gradient.

Front 23

Describe the principal of action of the Na+/K+ pump.

Back 23

1. Na+ binds to intracellular site

2. This triggers autophosphorylation of the pump

3. Phosphorylation causes a conformational change to release Na+ to the exterior and expose the K+ binding site

4. K+ binds, phosphate comes off protein

5. Pump returns to original conformation and the K+ is discharged into the interior of the cell

Front 24

How long is the whole process of the Na+/K+ pump action?

Back 24

10 ms

Front 25

The Na+/K+ ATPase is a drug target in the treatment of what disease?

Back 25

Congestive heart failure.

Front 26

What plant derived toxic substance can also bind to the K+ site?

Back 26

Oubain

Front 27

What is the NCX antiporter?

Back 27

An Na+/Ca2+ cotransporter protein that transports Ca 2+ out of the cell by using the concentration gradient of Na+.

Front 28

How is oubain used to treat congestive heart failure?

Back 28

1. Oubain inhibits the Na+/K+ ATPase by preventing K+ binding. This decreases the rate of extrusion of Na+ from cardiac muscle cells

2.Intracellular [Na+] increases so gradient of Na+ from outside to inside of cell is less, so NCX activity decreases.

3. Slower Ca 2+ efflux, and prolonged high cytosolic [Ca 2+] to maintain cardiac contraction.

Front 29

Describe the principle of action of the Na+/glucose transporter protein

Back 29

Uses gradient of sodium to drive transport of glucose into cells.

Front 30

Where is the Na+/glucose transporter important?

Back 30

1. Intestinal epithelial cells (absorption of dietary glucose).

2. Epithelial cells in the proximal tubules of the kidney for reabsorption of glucose from the primary urine.

Front 31

Describe the mechanism of action of the cholera toxin

Back 31

Front 32

Cholera toxin, produced by Vibrio cholerae causes hugeelectrolyte and fluid losses in the intestine. What is an example of replacement therapy?

Back 32

1. A high concentration of glucose, which drives Na+ back into the cell through the Na+/glucose transporter

2. Na+ is positive and attracts Cl- back into cell

3. Water follows

Front 33

What type of molecules are sucrose and glucose in terms of their charge, size and polarity?

Therefore can they move easily across the plasma membrane?

Back 33

Uncharged, large, polar

No

Front 34

What are some examples of hydrophobic molecules that can easily move across the membrane?

Back 34

Oxygen

Nitrogen

Benzene

Short chain fatty acids

Front 35

What are some small, uncharged polar molecules that can easily get across the membrane?

Back 35

Water

CO2

Glycerol

Urea

Front 36

What is the glucose transporter that transports glucose into hepatocytes?

Back 36

GLUT 2

(High Km and large Vmax. Transports glucose into hepatocytes when [glucose] is high, in order to regulate glucose levels)

Front 37

What is the glucose transporter found in muscle and adipocytes that is regulated by insulin ?

Back 37

GLUT 4

Front 38

Where is the GLUT 1 receptor expressed?

High or low Km?

Back 38

Ubiquitous;

abundant in erythrocytes, low in skeletal muscle

Low

Front 39

Where is the GLUT 2 receptor expressed?

High or low Km?

Back 39

Liver

Pancreatic β cells

High

Front 40

Where is the GLUT 3 receptor expressed?

High or low Km?

Back 40

Neurones

Low

Front 41

Where is the GLUT 4 receptor expressed?

What is its activity regulated by?

Back 41

Muscle, adipocytes

Insulin, which recruits GLUT 4 to plasma me,brane

Front 42

What is GLUT 5?

Back 42

Fructose transporter

Front 43

What is the concentration of chloride ions like on the inside of the cell compared to the outside?

Back 43

Inside = 4mM

Outside = 140 mM