Week 8 - Membrane Proteins and Transport (Part II)

Question 1

What do multi-pass transmembrane proteins create and for what function?

Answer 1

They create a protein-lined path across the cell membrane; to transport polar and uncharged particles

Question 2

Are transport proteins selective?

Answer 2

Yes; they transport a specific class of molecules.

Question 3

What is passive transport?

Answer 3

Movement down the concentration gradient; does NOT require energy; uses channel proteins.

Question 4

What is active transport?

Answer 4

Movement against the concentration gradient by transporter proteins; requires energy.

Question 5

What are the 2 types of transport proteins?

Answer 5

1. Channel proteins

2. Transporter proteins

Question 6

What are channel proteins?

Answer 6

A type of transport protein; do NOT interact much or bind strongly to the transported molecule. Passive Transport only.

Question 7

Do channel proteins change conformation?

Answer 7

They do not change conformation a lot.

Question 8

What are transporter (a.k.a. carrier) proteins?

Answer 8

A type of transport protein; interact a lot with and bind to the transported molecule. Passive and Active transport.

Question 9

Do carrier/transporter proteins change conformation?

Answer 9

Yes, they change to transport the solute across the membrane.

Question 10

What is resting membrane potential?

Answer 10

Membrane potential is an electrical gradient aiding in transport.

Question 11

What makes up the electrochemical gradient?

Answer 11

Concentration gradient + Membrane potential = Electrochemical gradient
The two gradient must be consider as they work against each other.

Question 12

Are channel proteins hydrophilic or hydrophobic?

Answer 12

They are hydrophilic pores across a membrane.

Question 13

Are channels or transporters faster at passive transport?

Answer 13

Channels are faster than transporters at passive transport as several molecules can pass through at once when open.

Question 14

What are the two types of ion-channels?

Answer 14

1. Non-gated ion channels

2. Gated ion channels

Question 15

Example of a non-gated ion channel?

Answer 15

Always open; K+ leak channels that play a major role in resting membrane potential in animal cells.

Question 16

What do gated-ion channels require to open?

Answer 16

Gated ion channels require signal to open; i.e. a chemical or electrical signal

Question 17

What do larger and small fonts represent on membrane diagrams?

Answer 17

Large font = higher concentration

Small font = lower concentration

Question 18

What are 4 kinds of GATED ion channels?

Answer 18

1. Voltage-gated
2. Mechanically-gated
3. Extracellular Ligand-gated
4. Intracellular Ligand-gated

Question 19

What do voltage-gated ion channels require?

Answer 19

A change in voltage across the membrane; a.k.a. membrane polarization and depolarization

Question 20

What do mechanically-gated ion channels require?

Answer 20

Mechanical stress; i.e. opening if the plasma membrane is stretched.

Question 21

Extracellular v.s. Intracellular ligands examples?

Answer 21

Extracellular ligand: neurotransmitters

Intracellular ligand: ions, nucleotides

Question 22

Do Uniporters do passive or active transport?

Answer 22

Passive transport by a transporter via facilitated diffusion; transport is reversible

Question 23

What is an example of a uniporter and how does it function?

Answer 23

GLUT uniporter; transports glucose down the electrochemical gradient. Can work in both directions.

Question 24

What are 3 types of active transport?

Answer 24

1. Co-transporters
2. ATP-driven pumps (a.k.a. Pumps or ATPases)
3. Light-driven pumps (i.e. bacteria)

Question 25

How do co-transporters move molecules?

Answer 25

They move one molecule down the gradient and one against the gradient.

Question 26

What is a symporter and what does it move?

Answer 26

An active transporter that move 2 molecules in the same direction.

Question 27

What is an antiporter and what does it move?

Answer 27

An active transporter that move 2 molecules in opposing directions.

Question 28

The free energy created from the co-transported ion moving down the electrochemical gradient does what?

Answer 28

Use the energy to transport the second molecule.

Question 29

In a Na+/Glucose symporter, what does moving Na+ down the electrochemical gradient do?

Answer 29

It provides energy to move glucose against the concentration gradient.

Question 30

What does cooperative binding of Na+ and glucose to a symporter lead to?

Answer 30

Leads to a conformational change in the protein.

Question 31

How is cytosolic pH (neutral) regulate?

Answer 31

Excess protons leak into the cell, produced by acid forming reactions; Na+ driven antiporters maintain pH.

Question 32

How does a Na+/H+ exchanger (antiporter) maintain cytosolic pH?

Answer 32

It responds to pH drops by increasing transporter activity; gets better at removing protons.

Question 33

How does a Na+/H+ exchanger (antiporter) move H+ out of the cell?

Answer 33

It uses the free energy stored in the Na+ electrochemical gradient to move the H+ out of the cell.

Question 34

As symporters and antiporters both use the sodium gradient to move molecules, what happens when the Na+ eventually gets equalized on both sides?

Answer 34

Na+/K+ pump (a transport ATPase) keeps the concentration different.

Question 35

What are P-type transport ATPases and what so they do?

Answer 35

P-type transport ATPases are ATP driven pumps that phosphorylate themselves to move molecules against the gradient.

Question 36

What does the Na+ gradient do?

Answer 36

- transports nutrients into cells | - maintenance of pH and cell volume

Question 37

What are the 8 steps of the pumping cycle of the Na+/K+ pump?

Answer 37

1. ATP bound to pump, 3 Na+ bind an open cytosolic pocket. 2. Pocket closes preventing Na+ escape. 3. ATP hydrolysis; pump phosphorylated, ADP released due to change in E1 conformation to E2 (phosphorylation). 4. E2 binding pocket exposed on the extracellular side; 3 Na+ exit. 5. 2K+ bind to E2. 6. Pocket closes preventing K+ escape. 7. Pump is de-phosphorylated. 8. ATP bind to pump to return to E1 state and K+ is released into cytosol.

Question 38

What happens when ATP binds to an E2 conformation of Na/K pump?

Answer 38

It changes back to E1 conformation and K+ is released.

Question 39

During ATP hydrolysis, what happens when the Na/K pump is phosphorylated?

Answer 39

ADP is released and E1 conformation changes to E2.

Question 40

Which conformation of the Na/K pump has ATP bound to it?

Answer 40

The E1 conformation has bound ATP. Change to E2 requires the phosphorylation of this ATP to occur.