Forces Acting Across Membranes 2

Question 1

Why is there a difference in charge across the plasma membrane?

Answer 1

The ions creating the concentration gradients are charged particles creating an electrical gradient

Question 2

What does the electrochemical gradient drive?

Answer 2

The direction of passive movement.

Question 3

What are 5 mechanisms of movement across the cell membrane?

Answer 3

• Endocytosis/ exocytosis
• Diffusion
• Mediated transport
• Osmosis
• Filtration

Question 4

What occurs in endocytosis?

Answer 4

There is invagination of the membrane to form a vesicle which eventually separates on the cytoplasmic surface of the membrane and migrates within the cell to its destination.

Question 5

What is exocytosis?

Answer 5

The reverse process of endocytosis

Question 6

What is diffusion?

Answer 6

Process by which a gas or substance in solution expands to fill all the available volume, therefore molecules spread from regions of high concentration to regions of low concentration until the concentration is uniform throughout the volume.

Question 7

What must be true of the barrier between 2 compartments for diffusion to take place?

Answer 7

It must be permeable to the diffusing substance

Question 8

How can the magnitude of net flux be described?

Answer 8

F=kpA(C1-C2)

The magnitude of diffusion is equal to the permeability coefficient multiplied by the surface area across which diffusion occurs multiplied by the difference in concentration

Question 9

What is the permeability coefficient?

Answer 9

A measure of the ease with which a molecule can pass through a given membrane

Question 10

What are cell memebrane effectively impermeable to?

Answer 10

Intracellular proteins and organic anions as they cannot diffuse in any capacity and so stay inside the cell.

Question 11

In order to diffuse through the lipid bilayer molecules need to be…

Answer 11

Small
Hydrophobic
Uncharged

Question 12

Why do ions such as Na, K and Cl cross membranes at a much faster rate than predicted?

Answer 12

The ions use transport proteins

Question 13

What are channel proteins?

Answer 13

Transmembrane IMPs that act as an aqueous route through the membrane for the diffusion of ions.

Question 14

What can pass through channels?

Answer 14

mineral ions such as Na, Cl, Ca, H and H2O

Question 15

Why can’t glucose pass through channels?

Answer 15

The channels are too small

Question 16

What does water pass through?

Answer 16

Aquaporins, a family of water channels

Question 17

What do channels consist of?

Answer 17

Multiple protein subunits

Question 18

How are gated channels opened?

Answer 18

They remain closed until a stimulus causes them to open. (stimulus can be chemical or a change in electrical charge across membrane)

Question 19

What are voltage gated channels reliant on?

Answer 19

Open/close in response to alterations in the membrane electrical potential (charge difference either side of the membrane)

Question 20

Where are voltage gated channels found mainly.

Answer 20

Muscle and nerve cells

Question 21

What are ligand gated channels reliant on?

Answer 21

Open/close when they bind a chemical such as a neurotransmitter or hormone to a receptor binding site on the channel protein

Question 22

What does the stimulus of a gated channel cause?

Answer 22

A conformational change of the channel protein causing it to open or close their channel.

Question 23

What is the direction of diffusion dependent on?

Answer 23

The concentration gradient and in the cases of charged particles, the electrical gradient.

Question 24

What is the membrane potential?

Answer 24

The inside of a cell usually carries a negative charge with respect to the outside if the cell.

Question 25

What does the membrane potential create?

Answer 25

A potential gradient down which ions will flow

Question 26

When is electrochemical equilibrium reached?

Answer 26

When the chemical and electrical gradients are in balance

Question 27

Facilitated diffusion

Answer 27

Movement of molecules through transport proteins down their electrochemical gradients

Question 28

Active Transport

Answer 28

Movement of molecules through transport proteins against their electrochemical gradients requiring energy (ATP)

Question 29

What happens when a solute binds to a carrier-mediated protein?

Answer 29

The carrier undergoes a change in shape which exposes the binding site on the other side of the membrane. The solute moves away and the carrier returns to its original conformation

Question 30

What is the function of the Na/K ATPase pump?

Answer 30

Occurs in all cells to help maintain the concentration gradient.

Question 31

What does the Na/K ATPase pump do?

Answer 31

Continuously pumps our 3 Na ions and pump 2 K ions into the cell

Question 32

What is produced by the Na/K ATPase pump?

Answer 32

A net movement of positive charges out of the cell

Question 33

Electrogenic Pump

Answer 33

A pump which creates a charge difference across the membrane

Question 34

How much of the resting energy of the body is used by the Na /K ATPase pump?

Answer 34

40%