Cell Biology For Bme: Chapter 12 - Membrane Transport

Front 1

What is a Transporter?

Back 1

It is class of membrane transport proteins that has moving parts to shift small molecules from one side of the membrane to the other.

Front 2

What is a Channel?

Back 2

It is a class of membrane transport proteins that form tiny hydrophilic pores in the membrane that solutes can pass by diffusion.

Front 3

What are the 5 most plentiful ions of all the solutes in a cell's environment?

Back 3

1. Na+
2. K+
3. Ca2+
4. Cl-
5. H+

Front 4

Is Na+ most plentiful inside or outside the cell? What about K+?

Back 4

Na+ is the most plentiful OUTSIDE the cell whereas K+ is the most plentiful INSIDE the cell

Front 5

If they're small enough, what 2 things can readily diffuse across the lipid bilayer? Give examples for both.

Back 5

1. Small nonpolar molecules (O2, CO2)
2. Uncharged polar molecules (water, ethanol)

Front 6

Lipid bilayers are highly impermeable to what?

Back 6

All ions and charged molecules, no matter how small.

Front 7

Membrane Transport Proteins fall into what 2 classes?

Back 7

1. Transporters
2. Channels

Front 8

Channels discriminate passage of molecules based on what two things?

Back 8

1. Size
2. Charge

Front 9

Transporters allow passage only to what?

Back 9

Molecules or ions that fit into a binding site on the protein!

Front 10

What is Passive Transport?

Back 10

Also called Facilitated Diffusion is diffusion down the concentration gradient (high to low) without using any energy

Front 11

What is Active Transport?

Back 11

Movement of a molecule across a membrane (usually from low to high concentrations) driven by ATP hydrolysis or another form of metabolic energy.

Front 12

The lysosome membrane contains what kind of transporter that acidifies the interior?

Back 12

H+ transporters!

Front 13

The inner membrane of mitochondria contains what kind of transporters so it can generate ATP and export it?

Back 13

Pyruvate transporters which is used for fuel for ATP generation

Front 14

What does Glucagon do?

Back 14

It stimulates the liver cells to produce large amounts of glucose by the breakdown of glycogen!

Front 15

How is the binding sites for glucose transport highly selective?

Back 15

The transporter will only bind D-glucose for transfer NOT L-glucose which cannot be used for glycolysis.

Front 16

What is Membrane Potential?

Back 16

Difference in the electrical potential on each side of the membrane

Front 17

Does the cytoplasmic side of the plasma membrane usually have positive or negative potential relative to the outside?

Back 17

Cytoplasmic side usually has a NEGATIVE potential (thus pulls positively charged solutes into the cell and negatively charged ones out of the cell.)

Front 18

What is Electrochemical Gradient?

Back 18

Gradient caused by both concentration gradients and voltage potential gradients across the membrane!

Front 19

What are the 3 main ways cells carry out active transport?

Back 19

1. Coupled transporters
2. ATP-driven pumps
3. Light-driven pumps

Front 20

What are coupled transporters?

Back 20

Active transporters that couple the uphill transport of one solute across the membrane to the downhill transport of another.

Front 21

What are ATP-Driven Pumps?

Back 21

Active transporter that couple uphill transport to the hydrolysis of ATP

Front 22

What are Light-Driven pumps?

Back 22

Active transporter mostly found in bacteria that couples uphill transport to the input of energy from light

Front 23

Animal cells use what to pump out Na+?

Back 23

The energy of ATP hydrolysis!

Front 24

The Na+ - K+ pump is also called what?

Back 24

Na-K ATPase

Front 25

The Na-K pump is not only a transporter. What is it also?

Back 25

An enzyme called an ATPase because it hydrolyzes ATP to ADP to transport Na+ out of the cell and K+ into the cell.

Front 26

What happens if ouabain is introduced to a cell?

Back 26

It halts the operation of the Na-K pump but the energy in this store is sufficient to sustain the cell for many minutes.

Front 27

What is the net driving force for movement of K+ across the membrane?

Back 27

Close to zero: electric force pulling K? into the cell is almost exactly balanced by the concentration gradient tending to drive it out.

Front 28

The Na-K pump is driven by the transient addition of what?

Back 28

The transient addition of a phosphate group!

Front 29

What are the 6 stages in the Na-K pump cycle?

Back 29

1. Na+ binds to pump
2. Pump phosphorylates itself
3. Phosphorylation triggers conformational change and Na+ is ejected into ECF
4. K+ binds
5. Pump is dephosphorylated
6. Pump returns to original conformation and K+ is ejected into ICF

Front 30

The net result of one cycle of the Na-K pump is the transport of how many Na+ and K+ ions?

Back 30

3 Na+ ions out of the cell and 2 K+ ions into the cell!

Front 31

What is Osmosis?

Back 31

The movement of water from low to high SOLUTE concentrations. (In other words, the movement of water from high to low WATER concentrations.)

Front 32

The driving force for the movement of water is what?

Back 32

The difference in water pressure called the Osmotic Pressure.

Front 33

In the absence of any counteracting pressure, the osmotic movement of water will cause a cell to do what?

Back 33

Swell

Front 34

What is Turgor Pressure?

Back 34

The pressure exerted by water inside the cell against the cell wall.

Front 35

Is Ca2+ kept in high or low concentrations in the cytosol?

Back 35

LOW concentrations!

Front 36

The downhill movement of the first solute down its gradient provides what?

Back 36

The energy to drive the uphill transport of the second solute!

Front 37

If the transporter moves both solutes in the same direction across the membrane, what is it called?

Back 37

Symport

Front 38

If the transporter moves moves two solutes in opposite directions, what is it called?

Back 38

Antiport!

Front 39

A transporter that ferries only one type of solute across the membrane is called what? Is it still a coupled transporter?

Back 39

Uniport! It is no longer considered a coupled transporter.

Front 40

What is a type of H+ pump in bacteria?

Back 40

Bacteriorhodopsin

Front 41

In animals, what is the purpose of an H+ pump found in some lysosomes?

Back 41

To pump H+ out of the cytosol to keep the pH of the cytosol neutral and the pH of the interior of the organelle acidic.

Front 42

Ion channels have what 2 important properties?

Back 42

1. Ion-selective
2. Gated

Front 43

Regarding ion channels, ion selectivity depends on what 3 things?

Back 43

1. diameter of channel
2. shape of channel
3. distribution of the charged amino acids that line the channel

Front 44

What is Patch-Clamp Recording?

Back 44

Technique in which the tip of a glass electrode is sealed into a patch of cell membrane, thereby making it possible to record the low of current through individual ion channels in the patch.

Front 45

Why is Patch-Clamp Recording important (think clamp)?

Back 45

Its ability to expose the membrane to different specific voltages makes it possible to see how changes in membrane potential affect the opening/closing of the channels.

Front 46

What is a Voltage-Gated Channel?

Back 46

Membrane protein that selectively allows ions to cross a membrane and is opened by changes in membrane potential.

Front 47

What is a Ligand-Gated Channel?

Back 47

An ion channel that opens when it binds a small molecule such as a neurotransmitter.

Front 48

What is a Stress-Gated Channel?

Back 48

Membrane protein that allows the selective entry of specific ions into a cell and is opened by mechanical force.

Front 49

What type of channel does the ear use to transmit sound signals to the brain?

Back 49

Stress-gated channels!

Front 50

Voltage-gated channels have specialized charged protein domains called what? What are they?

Back 50

Voltage sensors that are extremely sensitive to changes in the membrane potential.

Front 51

What are Leak Channels?

Back 51

Channels that randomly flicker between open and closed states no matter what the conditions are inside or outside the cell.

Front 52

What is the Resting Membrane Potential?

Back 52

Membrane potential in steady-state conditions (flow of positive and negative ions across membrane is precisely balanced)

Front 53

What is the Nernst Equation?

Back 53

Equation that expresses the equilibrium quantitatively and makes it possible to calculate the theoretical resting membrane potential if internal to external [ion] in known.

Front 54

What is the actual Nernst Equation assuming 37 C temperature?

Back 54

V = 62log(outside concentration/inside concentration)

Front 55

What is Curare?

Back 55

Drug that blocks the delivery of excitatory signals at neuromuscular junctions thus causing paralysis.

Front 56

What are the 2 common excitatory neurotransmitters?

Back 56

1. Acetylcholine
2. Glutamate

Front 57

What are the 2 main inhibitory neurotransmitters?

Back 57

1. GABA
2. Glycine

Front 58

Excitatory neurotransmitters activate ion channels that allow what ions passage?

Back 58

Na+ and Ca2+

Front 59

Inhibitory neurotransmitters activate ion channels that allow what ion passage?

Back 59

Cl-